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Sensory reweighting with translational visual stimuli in young and elderly adults: The role of state-dependent noise
Abstract
The properties of sensory reweighting for control of human upright stance have primarily been investigated through experimental techniques such as sinusoidal driving of postural sway. However, other forms of visual inputs that are commonly encountered, such as translation, may produce different adaptive responses. We directly compared sinusoidal and translatory inputs at stimulus parameters that made stimulus velocity comparable with each type of stimulus. Young healthy individuals were compared with healthy elderly and elderly designated as "fall-prone" to investigate whether the hypothesized basis for poor balance control in the "fall-prone" elderly is related to their ability to reweight sensory inputs appropriately. Standing subjects were presented with visual displays which moved in the medial-lateral direction either by (1) oscillating at different amplitudes or (2) simultaneously oscillating and translating at different speeds. All three subject groups showed that increasing the amplitude of the oscillations led to a decrease in gain. Increasing translation speed led to decreases in gain only at speeds above 1 cm/s. This suggests that the nervous system is processing more than just stimulus velocity to determine the postural response. A model implementing "state-dependent noise", in which visual stimulus noise increases with relative speed, was developed to account for the difference between translation and oscillation. The weak group effects question the common view that the fall-prone elderly are deficient in sensory reweighting. One explanation for the apparent discrepancy is that the slow, small-amplitude visual stimuli used in this study probe the asymptotic dynamics of the postural response. If given enough time, even the fall-prone elderly are able to adapt to a new sensory environment appropriately. However, the asymptotic adaptive response may not be functional in terms of preventing falls.
... An oscillating VR stimulus was presented as participants balanced on the rocker board to create a multisensory conflict. The degree to which the VR motion affected postural control was assessed by measuring the coupling between the frequency of stimulated VR oscillation to the amount of postural sway at that VR oscillation frequency, i.e., visual weighting (Wright et al. 2005;Jeka et al. 2006;Ma et al. 2022). In addition, power spectral density (PSD) at the frequency bands of 4-8 Hz (i.e., theta power) and 8-13 Hz (i.e., alpha power) were measured to identify cortical changes as participants were given different attentional focus instructions. ...
... Medial lateral (ML) displacement data were used to calculate the root mean square (RMS) of ML displacement (RMSd), RMS of ML velocity (RMSv), and total path length (i.e., total distance traveled in the ML direction) to examine overall postural stability during the task. Visual gain response was calculated to measure visual influence on postural sway (Wright et al. 2005;Jeka et al. 2006;Ma et al. 2022). Fast Fourier transforms of ML head displacement (output) and VR horizon angular displacement (input) were first performed to transform the time-series data into the frequency domain. ...
... Fast Fourier transforms of ML head displacement (output) and VR horizon angular displacement (input) were first performed to transform the time-series data into the frequency domain. The output-to-input magnitude (visual gain) was then calculated by dividing the frequency power of the output at 0.2 Hz over the frequency power of the input at 0.2 Hz (Wright et al. 2005;Jeka et al. 2006;Ma et al. 2022). Kinematic scores (i.e., visual gain, RMSd, RMSv, total path length) were mean averaged at each block. ...
Directing attention during balance training can have an immediate and lasting impact on a patient's balance and ultimately decrease the risk of future falls. However, it is unclear how attention can best be utilized to improve postural control. The current study uses a 2 × 2 crossover design to investigate the potential impact of receiving multiple verbal instructions during a single session of sensorimotor control testing for balance. Twenty-eight healthy adults were tasked to balance on a rocker board while immersed in virtual reality (VR). The VR created a multisensory mismatch between visual VR motion and body motion. The strength of the relationship between visual motion and body motion was measured to assess visual dependence. Alpha and theta frequency bands in electroencephalography (EEG) recordings were also analyzed to identify potential neural correlates of visual dependence and postural stability. Participants were randomized into two groups: one group was first instructed to keep the board leveled (external focus) and then instructed to keep both feet leveled (internal focus) to help maintain stability. The other group was given these two instructions in reverse order. Analyses focused on time, instruction, and group effects from receiving multiple instructions. Results revealed that when participants are given external focus first, and internal focus second, they are more likely to demonstrate lower visual dependence and better postural stability throughout the entire session than participants given internal focus first and external focus second. However, channel-level EEG analyses did not reveal differences between the groups. Current findings suggest that the order of attentional focus instructions may influence how the postural control system resolves sensory incongruence during a single testing session.
... The main issue of increased visual field dependence is the implication of reduced adaptive and attentional capacities, both of which may be improved with appropriate training. Sensory reweighting (and ultimately learning to identify and utilise more appropriate frames of reference with respect to task constraints) has been shown to improve with time and/or practice in both young (Brady et al., 2012) and old adults (Doumas & Krampe, 2010;Eikema et al., 2013;Jeka et al., 2006), while physical activity in general ameliorates both cognitive and physical capabilities affected by age (Seidler et al., 2010) and, in particular, preserves visuospatial functions (Shay & Roth, 1992). Furthermore, taking visual field dependence into account in rehabilitation programs for sedentary old adults can lead to optimizing the use of the visual frame of reference, rendering visual field dependence more functional -as is done for young adults (Yan, 2010) and ...
... While assessments of fall risk and postural control take into account the different sensory deficits and contributions to balance maintenance in old age (Callisaya et al., 2009;Lord & Ward, 1994;Wrisley & Kumar, 2010), if vision is manipulated, this tends to be simply eye closure. There is a multitude of research employing dynamic or rotated visual scenes which reveal whether visual input is upweighted (Borger et al., 1999;Eikema et al., 2012;Franz et al., 2015;Isableu et al., 1998;Isableu et al., 1997;Poulain & Giraudet, 2008;Slaboda et al., 2011;Streepey et al., 2007;Yeh et al., 2014) and also showing promise for implementation in rehabilitation protocols due to the improvements in postural control observed after multiple exposures to sensory discordance including perturbed visual input in both young healthy individuals (Pavlou et al., 2011) and in old adults and patients (Bugnariu & Fung, 2007;Jeka et al., 2006;O'Connor et al., 2008;Slaboda, Lauer, & Keshner, 2013). ...
... The task of stepping in place, however, proved to be optimal in revealing differential sensitivities to optic flow and further revealed that reduced exploitation of the egocentric FoR extends to self-motion perception in participants more reliant on the visual FoR. This is particularly interesting given the practical implementation of a stepping in place task in order to examine sensitivity to different visual input as has been done with neck muscle proprioceptive input (Bove, Courtine, & Schieppati, 2002) or further assess adaptations over time, i.e. whether egocentric information on self-motion is eventually upweighted and the visual influence attenuated as found in other studies (Doumas & Krampe, 2010;Jeka et al., 2006). Moreover, the practical aspect of stepping in place is already being exploited in virtual environment protocols due to the closeness of the task to actual walking (Nilsson, Serafin, & Nordahl, 2014;Templeman, Denbrook, & Sibert, 1999). ...
Aging entails deficits in the mechanisms of sensory integration which may affect daily living tasks in old adults, ultimately leading to loss of autonomy and health risks, notably falls. Among the factors contributing to these risks, some may be associated with a degradation in sensory (re)weighting, leading to a greater reliance on visual cues and the associated frames of reference (FoR) (visual field dependence).Our aim was to study how preferential modes of spatial referencing influence sensorimotor control. Examining visual field dependence in the context of aging thus allows to better understand:•if age-related cognition and/or sensorimotor deficits are associated with increased reliance on the visual FoR;•whether this reliance indicates a preferred mode of spatial referencing or a consequence of age-related deficits;•how the above associations and mechanisms evolve by studying young, middle-aged and old adults.We first examined possible factors associated with greater reliance on the visual FoR with age (Chapter 2). We confirmed classic literature reports of increased visual field dependence in old age, and uncovered an association between greater visual field dependence and reduced i) reliance on the egocentric FoR, ii) parallel attentional visual processing ability, and iii) visual fixation stability.We subsequently examined the orientation and stabilisation behaviour of our participants during postural tasks and while walking under different conditions of linear ground optic flow. In Chapter 3, participants stood quietly or stepped in place (SIP – intermittent podal contacts with the ground surface) while confronted with 1- natural optic flow (no stimulus), 2- a static visual stimulation, 3- approaching and 4- receding optic flow. The results showed that the optic flow stimuli influenced SIP primarily as evidenced by anteroposterior drifting of the head, trunk and centre of pressure (COP). Old adults had larger amplitudes of drift compared to the younger participants, and drifted even under natural flow (natural drift) during SIP, indicating reduced egocentric self-motion perception. The most important directional optic flow effects were on the COP and were associated with i) increased reliance on the visual FOR, ii) reduced reliance on the egocentric FoR, and iii) greater natural drift.In Chapter 4 we investigated the influence of ground optic flow on the control of walking and head stabilisation. Reliance on the visual FoR in old adults was manifested under conditions of i) natural flow by a reduced head pitch orientation and ability to stabilise their head in space, which may indicate a strategy to maximise the salience of available visual cues and ii) imposed optic flow, by a re-orientation of the trunk in pitch and increase in stepping frequency. Our results also revealed a general improvement of head stabilisation under conditions of imposed visual stimulation towards a more frequent adoption of the head stabilisation in space strategy. This suggests that the artificial enhancement of optic flow provokes a postural adaptation in order to optimise sensory information processing when walking.Our findings extend current knowledge on the association between reliance on the visual FoR and sensorimotor control across adulthood and depending on the perceptivo-motor task. It is evident that this reliance is linked to a reduction in the exploitation of the egocentric FoR in terms of body orientation and self-motion perception, and that its manifestation depends on the task. Finally, our work provides insights for the design of training protocols aimed at frailer olds taking into account exacerbated reliance on the visual FoR.
... These studies showed that healthy elderly individuals rely more on their visual information during standing balance compared with healthy young individuals (Bugnariu and Fung 2007;Faraldo-Garcia et al. 2012). Furthermore, it was shown that with age the nervous system loses ability to adapt to altered sensory conditions (Borger et al. 1999;Bugnariu and Fung 2007;Doumas and Krampe 2010;Eikema et al. 2012;Horak et al. 1989;Jeka et al. 2006;Stelmach and Worringham 1985;Teasdale et al. 1991;Teasdale and Simoneau 2001). ...
... Conclusions are only based on changes in CoP and CoM movement, while the contributions of the other underlying systems to these changes are not taken into account. System identification techniques potentially allow identification of the contribution of each individual system in maintaining an upright position and therefore allow investigation of the contribution of each sensory system regardless of changes in the other underlying systems involved in standing balance and compensation strategies used Engelhart et al. 2014a;Fitzpatrick et al. 1996;Jeka et al. 2006Jeka et al. , 2010Pasma et al. 2014;Peterka 2002;van der Kooij et al. 2005). Wellknown mechanical or sensory disturbances with specific frequency content are used to disturb specific underlying systems, such as proprioception, vision, and the leg or trunk segment. ...
... In elderly participants with impaired balance the results showed a higher proprioceptive weight compared with healthy elderly participants and no differences in proprioceptive downweighting. The included elderly participants with impaired balance had characteristics comparable to those of elderly with a history of falls included in previous studies investigating sensory integration Barrett et al. 2013;Jeka et al. 2006). Previous studies found a comparable sensory downweighting of visual information between fall-prone elderly participants with a history of unexplained falls and healthy elderly participants , which is in accordance with our study. ...
Using sensory reweighting reliable sensory information is selected over unreliable information during balance by dynamically combining this information. We used system identification techniques to show the weight and the adaptive process of weight change of proprioceptive information during standing balance with age and specific diseases. Ten healthy young, aged between 20 and 30 years, and 44 elderly, aged above 65 years, encompassing ten healthy elderly, ten with cataract, ten with polyneuropathy and fourteen with impaired balance, participated in the study. During stance, proprioceptive information of the ankles was disturbed by rotation of the support surface with specific frequency content where disturbance amplitude increased over trials. Body sway and reactive ankle torque were measured to determine sensitivity functions of these responses to the disturbance amplitude. Model fits resulted in a proprioceptive weight (changing over trials), time delay, force feedback, reflexive stiffness and damping. The proprioceptive weight was higher in healthy elderly compared to young and higher in elderly with cataract and with impaired balance compared with healthy elderly. Proprioceptive weight decreased with increasing disturbance amplitude; decrease was similar in all groups. In all groups, the time delay was higher and the reflexive stiffness was lower compared to young or to healthy elderly. In conclusion, proprioceptive information is weighted more with age, in patients with cataract and impaired balance. With age and specific diseases the time delay was higher and reflexive stiffness was lower. These results illustrate the opportunity to detect the underlying cause of impaired balance in elderly using system identification.
... Visual information determines the orientation of objects in space and the detection of body movements, including postural oscillations at rest (Lishman and Lee 1973;Prioli et al. 2005). Somatosensory information generated by muscle, joint and skin receptors encodes data on the relative position of the head, trunk and limbs in space Allison et al. 2006;Jeka et al. 2000). Finally, vestibular information encodes the position as well as linear and angular accelerations of the head, thus helping to inform the brain of its orientation and movements in relation to space (Peterka and Benolken 1995). ...
... To compensate for this deterioration, the brain reweighs the sources of sensory information according to their signal-to-noise ratio. Numerous studies suggest that the degeneration of the vestibular system (Rosenhall and Rubin 1975) and the accompanying decrease in the signalto-noise ratio of vestibular information may explain the preponderance of visual information during aging (Anson and Jeka 2016; Jeka et al 2006;Alberts et al. 2019) and in accompanying pathologies (Bronstein et al. 1996;Bronstein 1999;Guerraz et al. 2001;Lopez et al. 2007;Grabherr et al. 2011). This process of reweighting sensory information in favor of visual inputs would include the estimate of the vertical direction (Curthoys 2000;Peterka 2002;Peterka and Loughlin 2004). ...
Even for a stereotyped task, sensorimotor behavior is generally variable due to noise, redundancy, adaptability, learning or plasticity. The sources and significance of different kinds of behavioral variability have attracted considerable attention in recent years. However, the idea that part of this variability depends on unique individual strategies has been explored to a lesser extent. In particular, the notion of style recurs infrequently in the literature on sensorimotor behavior. In general use, style refers to a distinctive manner or custom of behaving oneself or of doing something, especially one that is typical of a person, group of people, place, context, or period. The application of the term to the domain of perceptual and motor phenomenology opens new perspectives on the nature of behavioral variability, perspectives that are complementary to those typically considered in the studies of sensorimotor variability. In particular, the concept of style may help toward the development of personalised physiology and medicine by providing markers of individual behaviour and response to different stimuli or treatments. Here, we cover some potential applications of the concept of perceptual-motor style to different areas of neuroscience, both in the healthy and the diseased. We prefer to be as general as possible in the types of applications we consider, even at the expense of running the risk of encompassing loosely related studies, given the relative novelty of the introduction of the term perceptual-motor style in neurosciences.
... Overall, the studies showed that the implicit information provided by two additional sensory cues [one from LT and other from visual stimuli, such as dynamic visual display Jeka et al., 2000)] offered simultaneously led to further reduction in the postural sway compared to that with only one additional sensory information. This reduction, however, was not due to an additive effect between sensorial inputs but to a sensory reweighting which was modulated by the quality, magnitude, velocity and nature of the stimuli ( Jeka et al., 2000Jeka et al., , 2006Oie et al., 2002;Polastri et al., 2012). ...
... The mechanisms which the postural control system integrates the additional sensory information from different cues to get a better perception of self-motion are still unclear. The current findings are in line from previous studies using two additional implicit sensory information ( Jeka et al., 2000Jeka et al., , 2006Oie et al., 2002;Polastri et al., 2012). Altogether, the findings provide support that there is not merely an algebraic summation of individual effects of the additional sensory sources to control the body position and reduce the postural sway. ...
The postural control is improved by implicit somatosensory information from lightly touching a rigid bar or explicit visual information about the postural sway. Whether these two additional sources provided at the same time further reduce the postural sway is still unknown. Participants stood on a force plate as quiet as possible lightly touching the bar while received or not visual feedback of the center of pressure position on a monitor screen. Postural sway reduced similarly with the light touch regardless of the additional visual feedback. The findings suggested that providing explicit visual feedback of the center of pressure does not increase the light touch effects on the postural sway. The importance of the implicit somatosensory information on postural control is discussed.
... Indeed, to some extent, physical activity performed on a regular basis may be able to protect the postural system from aging effects. To understand how aging and physical activity affect postural control, external perturbation techniques, more precisely sensory manipulation techniques (i.e., mechanical, electrical, chemical, optical) have been widely used (Gauchard et al., 2001(Gauchard et al., , 2003Hue et al., 2004;Jeka et al., 2006;Deshpande and Patla, 2007;Maitre et al., 2013aMaitre et al., ,b, 2015Eikema et al., 2014;Maitre and Paillard, 2016). The main objective of these techniques was to alter or manipulate sensory information (i.e., afferents emanating from the visual, vestibular and somatosensory systems) in order to analyze postural compensatory strategies, and to understand how individuals cope so that they can reorganize their posture in a challenging sensory context. ...
... Second, GVS induces an erroneous vestibular signal, which conflicts with afferent signals emanating from other sensory systems. In a context where one or more sensory systems give an erroneous signal, the CNS triggers a mechanism to adjust the sensory contributions of each sensory system in order to preserve postural control (Massion, 1994;Jeka et al., 2006). Regular physical activity may develop the specific ability to reweight sensory channels appropriately or to switch from one sensory channel to another one that is better adapted to the postural condition induced by the sensory manipulation (Vuillerme et al., 2001;Maitre et al., 2013b;Hopper et al., 2014;Paillard, 2017). ...
The aim of this study was to compare the ability of older individuals to maintain an efficient upright stance in contexts of vestibular sensory manipulation, according to their physical activity status. Two groups of healthy older women (aged over 65) free from any disorders (i.e., neurological, motor and metabolic disorders) and vestibular disturbances, participated in this study. One group comprised participants who regularly practiced gentle physical activities, i.e., soft gym, aquarobic, active walking, ballroom dancing (active group, age: 73.4 (5.8) years, n = 17), and one group comprised participants who did not practice physical activities (non-active group, age: 73.7 (8.1) years, n = 17). The postural control of the two groups was compared in a bipedal reference condition with their eyes open and two vestibular sensory manipulation conditions (i.e., bipolar binaural galvanic vestibular stimulation (GVS) at 3 mA, in accordance with two designs). The main results indicate that there was no difference between the active and the non-active groups in all the conditions. It is likely that the aging process and the type of physical practice had limited the ability of the active group to counteract the effects of vestibular sensory manipulation on postural control more efficiently than the non-active group.
... In addition, elderly people seem to have difficulties in sensory reweighting (Horak et al., 1989;Teasdale and Simoneau, 2001;Eikema et al., 2012Eikema et al., , 2014. The term "sensory reweighting" was established by Nashner et al. (1982) to describe a process of scaling the relative importance of sensory cues (visual, vestibular, and proprioceptive) for motor control (Nashner et al., 1982;Jeka et al., 2006). However, the sensory weighting process itself seems to be unimpaired in elderly people Jeka et al., 2006), indicating that differences in sensory weights between elderly and young people are related to different sensory preferences. ...
... The term "sensory reweighting" was established by Nashner et al. (1982) to describe a process of scaling the relative importance of sensory cues (visual, vestibular, and proprioceptive) for motor control (Nashner et al., 1982;Jeka et al., 2006). However, the sensory weighting process itself seems to be unimpaired in elderly people Jeka et al., 2006), indicating that differences in sensory weights between elderly and young people are related to different sensory preferences. ...
Multiple factors have been proposed to contribute to the deficits of postural control in the elderly. They were summarized as sensory, motor, and higher-level adaptation deficits. Using a model-based approach, we aimed to identify which of these deficits mainly determine age-related changes in postural control. We analyzed postural control of 20 healthy elderly people with a mean age of 74 years. The findings were compared to data from 19 healthy young volunteers (mean age 28 years) and 16 healthy middle-aged volunteers (mean age 48 years). Postural control was characterized by spontaneous sway measures and measures of perturbed stance. Perturbations were induced by pseudorandom anterior-posterior tilts of the body support surface. We found that spontaneous sway amplitude and velocity were significantly larger, and sway frequencies were higher in elderly compared to young people. Body excursions as a function of tilt stimuli were clearly different in elderly compared to young people. Based on simple feedback model simulations, we found that elderly favor proprioceptive over visual and vestibular cues, other than younger subjects do. Moreover, we identified an increase in overall time delay challenging the feedback systems stability, and a decline in the amplitude of the motor feedback, probably representing weakness of the motor system. In general, these parameter differences between young and old may result from both deficits and compensation strategies in the elderly. Our model-based findings correlate well with deficits measured with clinical balance scores, which are widely used in clinical practice.
... However, a similar pattern of phase increasing while gain decreases was reported with an oscillating-translational visual display movement in young adults (Ravaioli et al. 2005) and the elderly . The source of this phase dependency on condition, which indicates a nonlinear process, is unknown (Ravaioli et al. 2005;Jeka et al. 2006). ...
... However, the compensation may not be perfect. For example, it has been shown that the postural sway variability generally incrased when the gain to visual perturbation increased, indicating an incomplete compensation for the response to visual perturbation (Ravaioli et al. 2005;Jeka et al. 2006). ...
... Additionally, the generation of motor commands needed to balance with imposed delays may be compromised due to reduced muscular strength (Larsson et al., 1979;Kallman et al., 1990;Doherty, 2003), slower rates of muscle force production (Larsson et al., 1979;Thelen et al., 1996), longer reflex latencies (Dorfman and Bosley, 1979;Allum et al., 2002) and longer cognitive processing times (Lord and Fitzpatrick, 2001). Furthermore, when cognitive systems must accommodate more challenging balance conditions (Paillard, 2017;Ozdemir et al., 2018), such as standing with increasing delays, older adults may be hindered by age-related decline in cognitive function (Jeka et al., 2006;Lord et al., 2018;Wolpe et al., 2020). Considering these factors, the first aim of the present study was to determine whether learning to balance with long (250 ms) imposed sensorimotor delays differs between young and older healthy adults. ...
Background
While standing upright, the brain must accurately accommodate for delays between sensory feedback and self-generated motor commands. Natural aging may limit adaptation to sensorimotor delays due to age-related decline in sensory acuity, neuromuscular capacity and cognitive function. This study examined balance learning in young and older adults as they stood with robot-induced sensorimotor delays.
Methods
A cohort of community dwelling young (mean = 23.6 years, N = 20) and older adults (mean = 70.1 years, N = 20) participated in this balance learning study. Participants stood on a robotic balance simulator which was used to artificially impose a 250 ms delay into their control of standing. Young and older adults practiced to balance with the imposed delay either with or without visual feedback (i.e., eyes open or closed), resulting in four training groups. We assessed their balance behavior and performance (i.e., variability in postural sway and ability to maintain upright posture) before, during and after training. We further evaluated whether training benefits gained in one visual condition transferred to the untrained condition.
Results
All participants, regardless of age or visual training condition, improved their balance performance through training to stand with the imposed delay. Compared to young adults, however, older adults had larger postural oscillations at all stages of the experiments, exhibited less relative learning to balance with the delay and had slower rates of balance improvement. Visual feedback was not required to learn to stand with the imposed delay, but it had a modest effect on the amount of time participants could remain upright. For all groups, balance improvements gained from training in one visual condition transferred to the untrained visual condition.
Conclusion
Our study reveals that while advanced age partially impairs balance learning, the older nervous system maintains the ability to recalibrate motor control to stand with initially destabilizing sensorimotor delays under differing visual feedback conditions.
... Additionally, the generation of motor commands needed to balance with imposed delays may be compromised due to reduced muscular strength (Larsson et al., 1979;Kallman et al., 1990;Doherty, 2003), slower rates of muscle force production (Larsson et al., 1979;Thelen et al., 1996), longer reflex latencies (Dorfman and Bosley, 1979;Allum et al., 2002) and longer cognitive processing times (Lord and Fitzpatrick, 2001). Furthermore, when cognitive systems must accommodate more challenging balance conditions (Paillard, 2017;Ozdemir et al., 2018), such as standing with increasing delays, older adults may be hindered by age-related decline in cognitive function (Jeka et al., 2006;Lord et al., 2018;Wolpe et al., 2020). Considering these factors, the first aim of the present study was to determine whether learning to balance with long (250 ms) imposed sensorimotor delays differs between young and older healthy adults. ...
... Several studies propose that aged adults have difficulties with sensory reweighting [16,17]. On the other hand, other authors believe that the sensory reweighting process itself seems efficient in aged people for other authors [18,19]. This incoherence in the literature is probably related to the great heterogeneity of neuro-plastic capacities in the aged adults. ...
Background
Postural control is based on the integration of different sensory inputs. The process of scaling the relative importance of these sensory cues (visual, vestibular and proprioceptive) depends on individuals and creates sensory preferences, leading to sensory dependences when one particular source is preponderant. In this context, the literature showed a frequent visual dependence (visual inputs weighting) in aged adults. However, the somaesthetic inputs can also be prioritised in a podal-dependent profile. In the frail aged adults, none study has shown the distribution of these two dependences.
Research Question
Which sensory orientation profile is preferentially adopted by frail aged males and females?
Methods
In this cross-sectional study, we compared 33 frail aged adults to 16 non frail aged adults during a static postural control task in three conditions on a force platform: i) a standard condition, ii) a no-vision condition and iii) a foam condition. A analysis with the factor sex was also performed in each group of participants.
Results
The analysis of stabilometric parameters (mean velocity and mean velocity variance) highlighted a significant difference in no-vision or foam conditions when compared to the standard condition in frail aged males and only in the foam condition when compared to the standard condition for females in the frail group. No significant difference was observed between conditions in the control group.
Significance
Our study showed the predominance of both visual and podal information in frail aged adults when controlling their posture. Considering the sex factor, frail males were more dependents to their visual cues than frail females. This result should be used when designing the rehabilitation programs in this population.
... The participants in our study experienced increases of sway velocity of COG on a firm surface (when their eyes were closed) and also on a foam surface (eyes opened and closed). In the intervention group, this latter finding was likely related to a reduced sensitivity due to an overreliance on visual feedback (Yeh et al., 2014) that can disrupt balance when visual inputs are altered or unreliable (Jeka et al., 2006;O'Connor et al., 2008). Our intervention program reduced sway oscillations of COG on a firm surface (with EO and EC) and on a foam surface (EO and EC). ...
Objective: We investigated the effects of combined balance and strength training on measures of balance and muscle strength in older women with a history of falls. Methods: Twenty-seven older women aged 70.4 ± 4.1 years (age range: 65 to 75 years) were randomly allocated to either an intervention (IG, n = 12) or an active control (CG, n = 15) group. The IG completed 8 weeks combined balance and strength training program with three sessions per week including visual biofeedback using force plates. The CG received physical therapy and gait training at a rehabilitation center. Training volumes were similar between the groups. Pre and post training, tests were applied for the assessment of muscle strength (weight-bearing squat [WBS] by measuring the percentage of body mass borne by each leg at different knee flexions [0°, 30°, 60°, and 90°], sit-to-stand test [STS]), and balance. Balance tests used the modified clinical test of sensory interaction (mCTSIB) with eyes closed (EC) and opened (EO), on stable (firm) and unstable (foam) surfaces as well as spatial parameters of gait such as step width and length (cm) and walking speed (cm/s). Results: Significant group × time interactions were found for different degrees of knee flexion during WBS (0.0001 < p < 0.013, 0.441 < d < 0.762). Post hoc tests revealed significant pre-to-post improvements for both legs and for all degrees of flexion (0.0001 < p < 0.002, 0.697 < d < 1.875) for IG compared to CG. Significant group × time interactions were found for firm EO, foam EO, firm EC, and foam EC (0.006 < p < 0.029; 0.302 < d < 0.518). Post hoc tests showed significant pre-to-post improvements for both legs and for all degrees of oscillations (0.0001 < p < 0.004, 0.753 < d < 2.097) for IG compared to CG. This study indicates that combined balance and strength training improved percentage distribution of body weight between legs at different conditions of knee flexion (0°, 30°, 60°, and 90°) and also decreased the sway oscillation on a firm surface with eyes closed, and on foam surface (with eyes opened or closed) in the IG. Conclusion: The higher positive effects of training seen in standing balance tests, compared with dynamic tests, suggests that balance training exercises including lateral, forward, and backward exercises improved static balance to a greater extent in older women.
... The participants in our study experienced increases of sway velocity of COG on a firm surface (when their eyes were closed) and also on a foam surface (eyes opened and closed). In the intervention group, this latter finding was likely related to a reduced sensitivity due to an overreliance on visual feedback (Yeh et al., 2014) that can disrupt balance when visual inputs are altered or unreliable (Jeka et al., 2006;O'Connor et al., 2008). Our intervention program reduced sway oscillations of COG on a firm surface (with EO and EC) and on a foam surface (EO and EC). ...
Objective
We investigated the effects of combined balance and strength training on measures of balance and muscle strength in older women with a history of falls.
Methods
Twenty-seven older women aged 70.4 ± 4.1 years (age range: 65 to 75 years) were randomly allocated to either an intervention (IG, n = 12) or an active control (CG, n = 15) group. The IG completed 8 weeks combined balance and strength training program with three sessions per week including visual biofeedback using force plates. The CG received physical therapy and gait training at a rehabilitation center. Training volumes were similar between the groups. Pre and post training, tests were applied for the assessment of muscle strength (weight-bearing squat [WBS] by measuring the percentage of body mass borne by each leg at different knee flexions [0°, 30°, 60°, and 90°], sit-to-stand test [STS]), and balance. Balance tests used the modified clinical test of sensory interaction (mCTSIB) with eyes closed (EC) and opened (EO), on stable (firm) and unstable (foam) surfaces as well as spatial parameters of gait such as step width and length (cm) and walking speed (cm/s).
Results
Significant group × time interactions were found for different degrees of knee flexion during WBS (0.0001 < p < 0.013, 0.441 < d < 0.762). Post hoc tests revealed significant pre-to-post improvements for both legs and for all degrees of flexion (0.0001 < p < 0.002, 0.697 < d < 1.875) for IG compared to CG. Significant group × time interactions were found for firm EO, foam EO, firm EC, and foam EC (0.006 < p < 0.029; 0.302 < d < 0.518). Post hoc tests showed significant pre-to-post improvements for both legs and for all degrees of oscillations (0.0001 < p < 0.004, 0.753 < d < 2.097) for IG compared to CG. This study indicates that combined balance and strength training improved percentage distribution of body weight between legs at different conditions of knee flexion (0°, 30°, 60°, and 90°) and also decreased the sway oscillation on a firm surface with eyes closed, and on foam surface (with eyes opened or closed) in the IG.
Conclusion
The higher positive effects of training seen in standing balance tests, compared with dynamic tests, suggests that balance training exercises including lateral, forward, and backward exercises improved static balance to a greater extent in older women.
... Second, Jeka et al. (2006Jeka et al. ( , 2010 illustrated, in two studies, that poor balance control in the fall-prone elderly people was related to their inability to properly re-weight multisensory inputs. The ability to re-weight sensory inputs is important for postural control in elderly people. ...
Background: This systematic review pooled all the latest data and reviewed all the relevant studies to look into the effect of multisensory integration on the balance function in the elderly.
Methods: PubMed, Web of Science and Scopus were searched to find eligible studies published prior to May 2019. The studies were limited to those published in Chinese and English language. The quality of the included studies was assessed against the Newcastle-Ottawa Scale or an 11-item checklist, as recommended by Agency for Healthcare Research and Quality (AHRQ). Any disagreement among reviewers was resolved by comparing notes and reaching a consensus.
Results: Eight hundred thirty-nine records were identified and 17 of them were included for systematic review. The result supported our assumption that multisensory integration works on balance function in the elderly. All the 17 studies were believed to be of high or moderate quality.
Conclusions: The systematic review found that the impairment of multisensory integration could predispose elderly people to fall. Accurate assessment of multisensory integration can help the elderly identify the impaired balance function and minimize the risk of fall. And our results provide a new basis for further understanding of balance maintenance mechanism. Further research is warranted to explore the change in brain areas related to multisensory integration in the elderly.
... Mahboobin et al., 2005;Ravaioli et al., 2005). The results commonly show a greater amount of postural instability in older adults compared to young, suggesting that older adults are over-reliant on visual cues, and fail to use vestibular or proprioceptive cues to disambiguate the sense of self-motion, which could be fundamental to trips and falls in older adults (Eikema et al., 2012;Jeka et al., 2006;Sundermier et al., 1996). With regards to 'sensory integration' (the focus of the study presented here), experiments have demonstrated relatively faster detection of multisensory cues in older adults (Couth et al., 2018a;Hugenschmidt et al., 2009;Laurienti et al., 2006;Mahoney et al., 2011;Peiffer et al., 2007), as well as increased temporal (Poliakoff et al., 2006b;Setti et al., 2011aSetti et al., , 2011bVirsu et al., 2003) and spatial (Couth et al., 2016;Mahoney et al., 2014b;Poliakoff et al., 2006a) windows in which multisensory cues are integrated, compared to young adults. ...
Multisensory integration typically follows the predictions of a statistically optimal model whereby the contribution of each sensory modality is weighted according to its reliability. Previous research has shown that multisensory integration is affected by ageing, however it is less certain whether older adults follow this statistically optimal model. Additionally, previous studies often present multisensory cues which are conflicting in size, shape or location, yet naturally occurring multisensory cues are usually non-conflicting. Therefore, the mechanisms of integration in older adults might differ depending on whether the multisensory cues are consistent or conflicting. In the current experiment, young (n = 21) and older (n = 30) adults were asked to make judgements regarding the height of wooden blocks using visual, haptic or combined visual-haptic information. Dual modality visual-haptic blocks could be presented as equal or conflicting in size. Young and older adults' size discrimination thresholds (i.e. precision) were not significantly different for visual, haptic or visual-haptic cues. In addition, both young and older adults' discrimination thresholds and points of subjective equality did not follow model predictions of optimal integration, for both conflicting and non-conflicting cues. Instead, there was considerable between-subject variability as to how visual and haptic cues were processed when presented simultaneously. This finding has implications for the development of multisensory therapeutic aids and interventions to assist older adults with everyday activities, where these should be tailored to the needs of each individual.
... Specifically, previous evidence indicates that older adults are able to appropriately reconcile or adapt to conflicting cues to self-motion but that they are slower to do so. For instance, when older adults are presented with oscillatory visual cues while attempting to maintain a stable posture, they are more susceptible to postural sway than younger adults (e.g., Deshpande & Patla, 2007;Jeka et al., 2006); however, when older adults are exposed to the conflicting cues over a longer duration, they eventually adapt (e.g., Jeka et al., 2010). It is conceivable that in the current study, if motion cues were presented over a longer duration, older adults' response to spatial conflict may have been different. ...
Younger adults integrate visual and vestibular cues to self-motion in a manner consistent with optimal integration; however, little is currently known about whether this process changes with older age. Our objective was to determine whether older adults, like younger adults, display evidence of optimal visual–vestibular integration, including reductions in bimodal variance (Visual + Vestibular) compared with unimodal variance (visual or vestibular alone), and reliability-based cue weighting. We used a motion simulator and a head-mounted display to introduce a 2-interval forced-choice heading estimation task. Older (65+ years) and younger adults (18–35 years) judged which of two movements was more rightward. Movements consisted of vestibular cues (passive movement in darkness), visual cues (optic flow), or both cues combined. The combined condition contained either congruent cues or incongruent cues (either a subtle 5° or larger 20° conflict). Results demonstrated that older adults had less reliable visual heading estimates than younger adults but comparable vestibular heading estimates. During combined, congruent conditions, both age groups exhibited reductions in combined variance, consistent with predicted optimal integration. During subtle cue conflicts, only younger adults exhibited combined variance consistent with predicted optimal integration, but both age groups displayed reliability-based cue weighting. During larger spatial conflicts, neither group demonstrated optimal reductions in variance. Younger adults displayed reliability-based cue weighting but older adults’ heading estimates were biased toward the less reliable visual estimate. Older adults’ tendency to incorporate spatially conflicting and unreliable visual cues into their self-motion percept may affect their performance on mobility-related tasks like walking and driving.
... This might be due to slower central processing of sensory information 6) and slower adaptive multi-sensory reweighting 22) . Consequently, they lengthen the postural adaptation process and exhibit worse balance performance in more challenging sensory conditions 23) . ...
... Nevertheless, we cannot definitively exclude the possibility that our results would differ had we prescribed the same walking speed for all subjects. Prior studies [35,36], including a recent walking study [37], also show that people can and do adapt to optical flow perturbations, perhaps through a process of multisensory reweighting. Those studies in standing further support that age and falls history can slow this reweighting process compared to young adults [38]. ...
Background. Older adults are at an exceptionally high risk of falls, and most falls occur during locomotor activities such as walking. Reduced local dynamic stability in old age is often interpreted to suggest a lessened capacity to respond to more significant balance challenges encountered during walking and future falls risk. However, it remains unclear whether local dynamic stability during normal, unperturbed walking predicts the response to larger external balance disturbances.
Research question. We tested the hypothesis that larger values of local dynamic instability during unperturbed walking would positively correlate with larger changes thereof due to optical flow balance perturbations.
Methods. We used trunk kinematics collected in subjects across a spectrum of walking balance integrity – young adults, older non-fallers, and older fallers – during walking with and without mediolateral optical flow perturbations of four different amplitudes.
Results. We first found evidence that optical flow perturbations of sufficient amplitude appear capable of revealing independent effects of aging and falls history that are not otherwise apparent during normal, unperturbed walking. We also reject our primary hypothesis; a significant negative correlation only in young adults indicated that individuals with more local dynamic instability during normal, unperturbed walking exhibited smaller responses to optical flow perturbations. In contrast, most prominently in older fallers, the response to optical flow perturbations appeared independent of their baseline level of dynamic instability.
Significance. We propose that predicting the response to balance perturbations in older fallers, at least that measured using local dynamic stability, likely requires measuring that response directly.
... It is still under debate whether, in addition, elderly's central weighting of sensory signals is affected. While some authors reported an impaired sensory weighting (Teasdale and Simoneau, 2001;Eikema et al., 2014), others found it to be unimpaired (e.g., Allison et al., 2006;Jeka et al., 2006). This controversy is possibly caused by different experimental strategies to assess sensory weighting. ...
Objectives: Postural control in elderly people is impaired by degradations of sensory, motor, and higher-level adaptive mechanisms. Here, we characterize the effects of a progressive balance training program on these postural control impairments using a brain network model based on system identification techniques.
Methods and Material: We analyzed postural control of 35 healthy elderly subjects and compared findings to data from 35 healthy young volunteers. Eighteen elderly subjects performed a 10 week balance training conducted twice per week. Balance training was carried out in static and dynamic movement states, on support surfaces with different elastic compliances, under different visual conditions and motor tasks. Postural control was characterized by spontaneous sway and postural reactions to pseudorandom anterior-posterior tilts of the support surface. Data were interpreted using a parameter identification procedure based on a brain network model.
Results: With balance training, the elderly subjects significantly reduced their overly large postural reactions and approximated those of younger subjects. Less significant differences between elderly and young subjects' postural control, namely larger spontaneous sway amplitudes, velocities, and frequencies, larger overall time delays and a weaker motor feedback compared to young subjects were not significantly affected by the balance training.
Conclusion: Balance training reduced overactive proprioceptive feedback and restored vestibular orientation in elderly. Based on the assumption of a linear deterioration of postural control across the life span, the training effect can be extrapolated as a juvenescence of 10 years. This study points to a considerable benefit of a continuous balance training in elderly, even without any sensorimotor deficits.
... This might be due to slower central processing of sensory information 6) and slower adaptive multi-sensory reweighting 22) . Consequently, they lengthen the postural adaptation process and exhibit worse balance performance in more challenging sensory conditions 23) . ...
[Purpose] The aim of this study was to investigate the relationship of increased visual dependence to age, balance, attention, and vertigo. [Subjects and Methods] Twelve younger, 12 visually independent (VI) older and 12 visually dependent (VD) older adults were assessed for levels of visual dependence using Subjective Visual Vertical (SVV) tilt values, balance ability using the Clinical Test of Sensory Integration for Balance (CTSIB), and attentional requirements through the dual-task paradigm and experience of vertigo by completing the Situational Vertigo Questionnaire (SVQ). [Results] VD older adults had higher SVV tilt values, greater postural sway in a scenario where visual and proprioceptive inputs were simultaneously altered, similar dual-task cost and lower SVQ scores compared with younger and VI older adults. No difference was observed between the latter two. [Conclusion] Visual dependence may not necessarily increase with age but affect balance in a sensory condition involving visual-proprioceptive conflict. There is a non-significant trend for elevated visual dependence with increased attentional demands. Greater visual dependence is not accompanied by more frequent symptoms of vertigo in visually complex environments.
... The second potential mechanism is linking VF with falls in the impact on balance; specifically, the impact of VF on sensory integration important for postural control. Effective integration of multisensory information (i.e., vision, proprioception, and vestibular inputs) is a process often termed "sensory re-weighting" (Peterka 2002;Mahboobin et al. 2005Mahboobin et al. , 2009Jeka et al. 2006;Peterka 2014, 2016;Logan et al. 2014). This process involves resolving conflicting sensory inputs if two or more channels provide contradictory body state-related information and relies on accurate sensory channels to generate postural adjustments if one or more afferent inputs are inaccurate/noisy or absent (Peterka 2002;Peterka 2014, 2016). ...
Vision impairments such as age-related macular degeneration (AMD) and glaucoma are among the top risk factors for geriatric falls and falls-related injuries. AMD and glaucoma lead to loss of the central and peripheral visual fields, respectively. This study utilized a custom contact lens model to occlude the peripheral or central visual fields in healthy adults, offering a novel within-subject approach to improve our understanding of the etiology of balance impairments that may lead to an increased fall risk in patients with visual field loss. Two dynamic posturography tests, including an adapted version of the Sensory Organization Test and a virtual reality environment with the visual scene moving sinusoidally, were used to evaluate standing balance. Balance stability was quantified by displacement and time-normalized path length of the center of pressure. Nine young and eleven older healthy adults wore visual field occluding contact lenses during posturography assessments to compare the effects of acute central and peripheral visual field occlusion. The results found that visual field occlusion had greater impact on older adults than young adults, specifically when proprioceptive cues are unreliable. Furthermore, the results suggest that both central and peripheral visions are important in postural control; however, peripheral vision may be more sensitive to movement in the environment.
... A greater inter-individual difference in older adults was observed from scatter graphs. In fact multiple studies report that balance degeneration with age is not necessarily linear [21][22][23]. Some older subjects had similar or even lower SVV tilt values than younger ones [5,6,24]. ...
... Older adults are also less precise than younger adults when making absolute heading judgments such that, when asked to indicate the angle of a linear motion on a scale, their mean heading estimation errors are greater than those displayed by younger adults (Lich & Bremmer, 2014). Furthermore, when physically translating in total darkness and thereby relying predominantly upon the vestibular system to perceive the direction of their movement (i.e., left-right, forwardbackward), older adults require a higher rate of acceleration in order to reliably discern Lamontagne, 2009;Deshpande & Patla, 2007;Jeka et al., 2006;Stapleton, Setti, Doheny, Kenny, & Newell, 2014). Further, when having to use self-motion cues to update their position in space (i.e., path integration; Mittelstaedt & Mittelstaedt, 1980), older adults demonstrate greater performance decrements relative to younger adults when they are restricted to using either vestibular or proprioceptive input alone (e.g., Adamo, Bricen˜o, Sindone, Alexander, & Moffat, 2012) or visual input alone (e.g., Harris & Wolbers, 2012) compared with when both cues are available. ...
Previous psychophysical research has examined how younger adults and non-human primates integrate visual and vestibular cues to perceive self-motion. However, there is much to be learned about how multisensory self-motion perception changes with age, and how these changes affect performance on everyday tasks involving self-motion. Evidence suggests that older adults display heightened multisensory integration compared with younger adults; however, few previous studies have examined this for visual–vestibular integration. To explore age differences in the way that visual and vestibular cues contribute to self-motion perception, we had younger and older participants complete a basic driving task containing visual and vestibular cues. We compared their performance against a previously established control group that experienced visual cues alone. Performance measures included speed, speed variability, and lateral position. Vestibular inputs resulted in more precise speed control among older adults, but not younger adults, when traversing curves. Older adults demonstrated more variability in lateral position when vestibular inputs were available versus when they were absent. These observations align with previous evidence of age-related differences in multisensory integration and demonstrate that they may extend to visual–vestibular integration. These findings may have implications for vehicle and simulator design when considering older users.
... In this paper we have focused solely on mechanical disturbances, which are often aimed to identify deteriorations in the nervous system part of the control and in the strategies used (ankle or hip strategy). In addition, sensory disturbances can be used to quantify the visual, proprioceptive, and vestibular contributions to maintain standing balance ( Peterka, 2002;Jeka et al., 2006;Pasma et al., 2012 ). ...
The incidence of impaired balance control and falls increases with age and disease and has a significant impact on daily life. Detection of early-stage balance impairments is difficult as many intertwined mechanisms contribute to balance control. Current clinical balance tests are unable to quantify these underlying mechanisms, and it is therefore difficult to provide targeted interventions to prevent falling. System identification techniques in combination with external disturbances may provide a way to detect impairments of the underlying mechanisms. This is especially challenging when studying multi-joint coordination, i.e. the contribution of both the ankles and hips to balance control.
... We interpret these results to mean that older adults are unable to ignore visual feedback about their COP (even with a time delay), which in turn decreases postural control. This interpretation is supported by previous results observed by Jeka et al. (2006), who suggested that older adults are unable to suppress unreliable visual cues when they are exposed to visual motion stimuli. It is also possible that the age-related decline in cognition may impair one's ability to perform an attentional switch. ...
Background/study context:
A manipulation check was used to investigate whether there is an age-related difference in the adherence to specific external- and internal-focus instructional constraints.
Methods:
Participants stood on a force platform and were to maintain a feedback cursor (representing their center of pressure) along the horizontal direction, within a target on a computer monitor. Trials were conducted with either an external focus of attention (keeping the feedback cursor within the target) or an internal focus of attention (keeping the weight evenly distributed between both legs).
Results:
The finding showed that younger adults followed the experimental instructions; however, older adults relied on external visual information when they were asked to focus on the body movements.
Conclusion:
Age-related declines may contribute to attention allocation differences. The authors propose that specific manipulation checks be used to ensure proper adherence to instructions when comparing age-related differences in postural control.
... Another study using visual and light touch displays has shown that children between 4-10 years old increased the amount of re-weighting as age, indicating the developmental process of a adaptive ability (Bair, Kiemel, Jeka, & Clark, 2007). On the other hand, it has been evidenced that elderly adults have less efficient in sensory re-weighting ability from the computer-simulated display experiments of quiet standing tasks (Jeka et al., 2006) and collision avoidance tasks (Eikema, Hatzitaki, Tzovaras, & Papaxanthis, 2012). In one of the latest synthesizing experimental settings, the visual, vestibular, and proprioceptive inputs were simultaneously perturbed with a random texture on a surrounded screen, galvanic vestibular stimulation, and vibrator on the Achilles tendons, respectively ( Figure 4) (Hwang, Agada, Kiemel, & Jeka, 2014). ...
Our world never seems to stop computerization. Thus, we must work effectively with computer displays in our daily lives. This is often the case for experimental participants who are instructed to respond to computer-generated visual stimuli. This chapter reviews the literature on human visuomotor behaviors, for which computer-simulated displays, such as virtual reality, served as a tool of stimulus presentation. At the beginning a brief technical overview is provided, followed by arguments on the findings derived from the investivgations of several representative perceptual motor tasks. In studies on posture control, immersive and interactive visual environments are useful to examine the balance response to an apparent motion in the visual scene, known as optical flow. With regard to interceptive action, various types of environments have been utilized depending on tasks, although stereoscopic displays seem to be a technique of choice. For biological motion perception, computer-generated graphical characters can be an alternative to the simple traditional model called point-light display. Some recent topics are also provided, in which computer-simulated displays are effectively utilized to address longstanding scientific problems. At the end of the review, the results from comparisons between simulation and reality are presented in order to highlight the specific effect of computer-generated stimuli on the viewer's response. Researchers should thoroughly recognize the advantages and disadvantages of a computer-simulated display, and at times, may need to consider whether the visual stimuli on the screen evoke valid visuomotor responses that meet the purpose of their study.
... Similar to reports of experimental sensory reweighting, studies reporting that proprioception can be altered in elderly individuals have been reviewed by Goble et al. (2009) and Shaffer and Harrison (2007). Recently, it was reported that the effects of visual cues with oscillation, as well as with oscillation and transition, show only marginal differences between young, elderly, and fall-prone elderly individuals (Jeka et al., 2006). Vestibular dysfunction in elderly, healthy elderly, and healthy younger adults has been compared using SOT, and the results indicated that visual and vestibular functions exhibited significantly more age-related weakening than did proprioception (Pedalini et al., 2009). ...
Posture control to maintain an upright stance is one of the most important and basic requirements in the daily life of humans. The sensory inputs involved in posture control include visual and vestibular inputs, as well as proprioceptive and tactile somatosensory inputs. These multisensory inputs are integrated to represent the body state (body schema); this is then utilized in the brain to generate the motion. Changes in the multisensory inputs result in postural alterations (fast dynamics), as well as long-term alterations in multisensory integration and posture control itself (slow dynamics). In this review, we discuss the fast and slow dynamics, with a focus on multisensory integration including an introduction of our study to investigate "internal force control" with multisensory integration-evoked posture alteration. We found that the study of the slow dynamics is lagging compared to that of fast dynamics, such that our understanding of long-term alterations is insufficient to reveal the underlying mechanisms and to propose suitable models. Additional studies investigating slow dynamics are required to expand our knowledge of this area, which would support the physical training and rehabilitation of elderly and impaired persons.
... The main issue of increased visual field dependence is the implication of reduced adaptive and attentional capacities, both of which may be improved with appropriate training. Sensory reweighting (and ultimately learning to identify and utilize more appropriate frames of reference with respect to task constraints) has been shown to improve with time and/or practice in both young (Brady et al. 2012) and old adults (Doumas and Krampe 2010;Eikema et al. 2013;Jeka et al. 2006), while physical activity in general ameliorates both cognitive and physical capabilities affected by age (Seidler et al. 2010) and, in particular, preserves visuospatial functions (Shay and Roth 1992). Furthermore, taking visual field dependence into account in rehabilitation programs for sedentary old adults can lead to optimizing the use of the visual frame of reference, rendering visual field dependence more functional-as is done for young adults (Yan 2010) and Parkinson's patients (Azulay et al. 2006). ...
Reliance on the visual frame of reference for spatial orientation (or visual field dependence) has been reported to increase with age. This has implications on old adults' daily living tasks as it affects stability, attention, and adaptation capacities. However, the nature and underlying mechanisms of this increase are not well defined. We investigated sensorimotor and cognitive factors possibly associated with increased visual field dependence in old age, by considering functions that are both known to degrade with age and important for spatial orientation and sensorimotor control: reliance on the (somatosensory-based) egocentric frame of reference, visual fixation stability, and attentional processing of complex visual scenes (useful field of view, UFOV). Twenty young, 18 middle-aged, and 20 old adults completed a visual examination, three tests of visual field dependence (RFT, RDT, and GEFT), a test of egocentric dependence (subjective vertical estimation with the body erect and tilted at 70°), a visual fixation task, and a test of visual attentional processing (UFOV®). Increased visual field dependence with age was associated with reduced egocentric dependence, visual fixation stability, and visual attentional processing. In addition, visual fixation instability and reduced UFOV were correlated. Results of middle-aged adults fell between those of the young and old, revealing the progressive nature of the age effects we evaluated. We discuss results in terms of reference frame selection with respect to ageing as well as visual and non-visual information processing. Inter-individual differences amongst old adults are highlighted and discussed with respect to the functionality of increased visual field dependence.
... Of note here is the fact that during the experiment, special attention was given to maintain a consistent stance width across all trials performed in both directions. AP tracking was expected to result in greater entrainment than tracking in the ML direction because visual information about self-motion and orientation is available predominantly in the AP [33,34]and to a lesser extent in the ML direction [35]. Nevertheless, tracking of a target moving in the vertical direction by voluntarily swaying in the sagittal plane required an additional coordinate transformation between the target's screen (up-down) and the body's spatial (forward-backward) coordinates which increased the computational load of the tracking task. ...
Variability is an inherent and important feature of human movement. This variability has form exhibiting a chaotic structure. Visual feedback training using regular predictive visual target motions does not take into account this essential characteristic of the human movement, and may result in task specific learning and loss of visuo-motor adaptability. In this study, we asked how well healthy young adults can track visual target cues of varying degree of complexity during whole-body swaying in the Anterior-Posterior (AP) and Medio-Lateral (ML) direction. Participants were asked to track three visual target motions: a complex (Lorenz attractor), a noise (brown) and a periodic (sine) moving target while receiving online visual feedback about their performance. Postural sway, gaze and target motion were synchronously recorded and the degree of force-target and gaze-target coupling was quantified using spectral coherence and Cross-Approximate entropy. Analysis revealed that both force-target and gaze-target coupling was sensitive to the complexity of the visual stimuli motions. Postural sway showed a higher degree of coherence with the Lorenz attractor than the brown noise or sinusoidal stimulus motion. Similarly, gaze was more synchronous with the Lorenz attractor than the brown noise and sinusoidal stimulus motion. These results were similar regardless of whether tracking was performed in the AP or ML direction. Based on the theoretical model of optimal movement variability tracking of a complex signal may provide a better stimulus to improve visuo-motor adaptation and learning in postural control.
... One possible predictor is visual control of posture: that is, the extent to which people rely on visual cues to maintain steady upright posture. While much study has examined postural control in the areas of ageing [3,4], balance-related disorders such as Parkinson's Disease [5,6], and, in some cases, multisensory integration [7][8][9], few studies have examined its role in self-motion perception. ...
Visually-induced illusions of self-motion (vection) can be compelling for some people, but they are subject to large individual variations in strength. Do these variations depend, at least in part, on the extent to which people rely on vision to maintain their postural stability? We investigated by comparing physical posture measures to subjective vection ratings. Using a Bertec balance plate in a brightly-lit room, we measured 13 participants’ excursions of the centre of foot pressure (CoP) over a 60-second period with eyes open and with eyes closed during quiet stance. Subsequently, we collected vection strength ratings for large optic flow displays while seated, using both verbal ratings and online throttle measures. We also collected measures of postural sway (changes in anterior-posterior CoP) in response to the same visual motion stimuli while standing on the plate. The magnitude of standing sway in response to expanding optic flow (in comparison to blank fixation periods) was predictive of both verbal and throttle measures for seated vection. In addition, the ratio between eyes-open and eyes-closed CoP excursions during quiet stance (using the area of postural sway) significantly predicted seated vection for both measures. Interestingly, these relationships were weaker for contracting optic flow displays, though these produced both stronger vection and more sway. Next we used a non-linear analysis (recurrence quantification analysis, RQA) of the fluctuations in anterior-posterior position during quiet stance (both with eyes closed and eyes open); this was a much stronger predictor of seated vection for both expanding and contracting stimuli. Given the complex multisensory integration involved in postural control, our study adds to the growing evidence that non-linear measures drawn from complexity theory may provide a more informative measure of postural sway than the conventional linear measures.
... Of note here is the fact that during the experiment, special attention was given to maintain a consistent stance width across all trials performed in both directions. AP tracking was expected to result in greater entrainment than tracking in the ML direction because visual information about self-motion and orientation is available predominantly in the AP [33,34]and to a lesser extent in the ML direction [35]. Nevertheless, tracking of a target moving in the vertical direction by voluntarily swaying in the sagittal plane required an additional coordinate transformation between the target's screen (up-down) and the body's spatial (forward-backward) coordinates which increased the computational load of the tracking task. ...
... A number of studies have shown that the sensory receptors that monitor body orientation are less sensitive in older adults (see [4]; [5] for a review). This reduced sensitivity has been linked to falling [6] and overreliance on visual feedback [7][8][9], which can disrupt postural control when visual inputs are altered or unreliable [10][11][12]. In addition to reductions in sensory reliability, delays in the transmission of feedback from the lower limb can exceed several tens of milliseconds [13]. ...
Sensory information from our eyes, skin and muscles helps guide and correct balance. Less appreciated, however, is that delays in the transmission of sensory information between our eyes, limbs and central nervous system can exceed several 10s of milliseconds. Investigating how these time-delayed sensory signals influence balance control is central to understanding the postural system. Here, we investigate how delayed visual feedback and cognitive performance influence postural control in healthy young and older adults. The task required that participants position their center of pressure (COP) in a fixed target as accurately as possible without visual feedback about their COP location (eyes-open balance), or with artificial time delays imposed on visual COP feedback. On selected trials, the participants also performed a silent arithmetic task (cognitive dual task). We separated COP time series into distinct frequency components using low and high-pass filtering routines. Visual feedback delays affected low frequency postural corrections in young and older adults, with larger increases in postural sway noted for the group of older adults. In comparison, cognitive performance reduced the variability of rapid center of pressure displacements in young adults, but did not alter postural sway in the group of older adults. Our results demonstrate that older adults prioritize vision to control posture. This visual reliance persists even when feedback about the task is delayed by several hundreds of milliseconds.
... This amplitude dependence of the temporal stability is not consistent with the predictions about phase from the adaptive postural model [26,27] which suggests that phase remains roughly constant when stimulus amplitudes are changed. Previous results have shown this phase pattern for adults and elderly individuals [20,41] which has been suggested to be caused by an increase in the stiffness of the postural control [20]. However, these aspects remain unknown and need to be examined further. ...
This study investigated how children's postural control adapts to changes in the visual environment and whether they use previous experience to adjust postural responses to following expositions. Four-, eight-, and twelve-year-old children (10 in each group) and 10 young adults stood upright inside of a moving room during eight trials each lasting one-minute. In the first trial, the room was stationary. In the following seven trials, the room oscillated at 0.2 Hz, amplitude of 0.5 cm, with the exception of the fifth trial, in which the room oscillated with amplitude of 3.2 cm. Body sway responses of young adults and older children down-weighted more to the increased visual stimulus amplitude when compared to younger children. In addition, four- and eight-year-old children quickly up-weighted body responses to visual stimulus in the subsequent two trials after the high amplitude trial. Sway variability decreased with age and was greatest during the high-amplitude trial. These results indicate that four year olds have already developed the adaptive capability to quickly down-weight visual influences. However, the increased gain values and residual variability observed for the younger children suggest that they have not fully calibrated their adaptive response to that of the young adults tested. Moreover, younger children do not carry over their previous experience from the sensorial environment to adapt to future changes.
... The specific mechanisms implicated in this interference are not fully understood yet but there are several suggestions that executive functions (and working memory subprocesses) are involved. Evidences also have been provided that older individuals have difficulties in adapting to new sensory contexts (Jeka et al. 2006(Jeka et al. , 2010Teasdale et al. 1991;Teasdale and Simoneau 2001). When standing, performing the tracing task with mirror-reversed vision implies the brain needs to attenuate proprioceptive signals from the upper arm (as discussed above), but not those related to body sway as these later signals contribute to preserving equilibrium. ...
When tracing a template with mirror-reversed vision (or distorted vision), the sensory information arising from the movement does not match the expected sensory consequences. In such situations, participants have to learn a new visuomotor mapping in order to trace the template with an accuracy and speed approaching that observed when tracing with direct vision. There are several suggestions that such visuomotor learning requires lowering the gain of the proprioceptive inputs. Generally, subjects learn this task in a seated condition offering a stable postural platform. Adapting to the new visuomotor relationship in a standing condition could add complexity and even hinder sensorimotor adaptation because balance control and processing of additional information typically interfere with each other. To examine this possibility, older individuals and young adults (on average, 70 and 22 years of age, respectively) were assigned to groups that trained to trace a shape with mirror-reversed vision in a seated or a standing condition for two sessions. For a third session, the seated groups (young and elderly) transferred to the standing condition while the standing groups continued to perform the tracing task while standing. This procedure allowed comparing the tracing performance of all groups (with the same amount of practice) in a standing condition. The standing groups also did a fourth session in a seated condition. Results show that older participants initially exposed to the standing condition were much slower to trace the template than all other groups (including the older group that performed the tracing task while seated). This slowness did not result from a baseline general slowness but from a genuine interference between balance control and the visuomotor conflict resulting from tracing the pattern with mirror-reversed vision. Besides, the Standing-Old participants that transferred to a seated condition in the fourth session immediately improved their tracing by reducing the total displacement covered by the pen to trace the template. Interestingly, the results did not support a transfer-appropriate practice hypothesis which suggests that training in a standing condition (at the third session) should have benefited the performance of those individuals who initially learned to trace the mirror pattern in a standing condition. This has important clinical implications: training at adapting to new sensory contexts or environmental conditions in conditions that do not challenge balance control could be necessary if one desires to attenuate the detrimental consequences on the postural or motor performances brought up by the interference between maintaining balance and the sensory reweighing processes.
... In contrast, the inability to weight certain sensory inputs to activate the most efficient and effective postural motor adjustments has been implicated in individuals with postural control impairments and motor deficits. 20 Sensory weighting between visual and tactile subsystems as a potential mechanism for balance and postural control impairments has not been examined in children with FASD. In addition, manipulations to discover vestibular weighting capabilities in both children with FASD and children with typical development (TD) have not been studied. ...
Background
Inefficient central processing and integration of visual, vestibular, and somatosensory information may contribute to poor balance and diminished postural control in children with fetal alcohol spectrum disorders (FASD).Objectives
This pilot study examined sensorimotor performance and the sensory control of balance using a battery of clinical tests in combination with an experimental laboratory assessment that quantifies sensory subsystem use (i.e., sensory weighting) among a systematically diagnosed sample of children with FASD and children with typical development.Methods
Using a case-control design, 10 children with FASD (8.0-15.9 years; 20% female) were compared to 10 age- and sex-matched controls on standardized clinical measures and on kinematic outcomes from the Multimodal Balance Entrainment Response system (MuMBER), a computerized laboratory assessment whereby visual, vestibular, and somatosensory input is manipulated at different frequencies during standing balance.ResultsChildren with FASD showed poorer sensorimotor performance across clinical outcomes with significant group differences (p < .05) on parent-reported movement behaviors (Sensory Processing Measure and Movement Assessment Battery for Children-2 Checklist) and performance on the Dynamic Gait Index. Experimental kinematic outcomes yielded statistically significant group differences (p <.10) on a small proportion of somatosensory and vestibular sensory weighting fractions and postural sway velocity in response to the manipulation of sensory input.Conclusions
Preliminary findings showed small group differences in sensorimotor and sensory weighting behaviors, specifically those that rely on the integration of vestibular sensation. Differences must be examined and replicated with a larger sample of children with FASD to understand the impact on balance control and functional sensorimotor behaviors.
... Accordingly, the weight on a reference frame (modality) may need to be mod ified[24], because of changing environmental conditions, with this sensory reweighting process being critical for perceptuomotor control[3] and maintaining postural stability in a dynamic environment[6]. In particular, since it accurately represents the orientation of the environment, a stationary full field v isual stimu lus provides a useful reference therefore its associated weight will increase to improve postural stability[13, 15]. However, when static visual frames of reference are tilted, they can induce postural t ilt or sway in standing observers, because such visual cues conflict with other egocentric cues to spatial orientation[11], therefore, the weight assigned to the visual channel needs to be reduced in order to preserve balance. ...
Th is study tested the effects of perceived t ime pressure on subjective visual vertical (SVV) perception in co llege healthy male students. Delayed down-weighting of inaccurate visual cues has been imp licated in age-induced overreliance on visual informat ion, which may be disruptive for postural control. Accordingly, I hypothesized that under time pressure, participants may not have enough time to downgrade the distracting visual input fro m the tilted frame and display larger rod-and-frame effects (RFE) on a co mputerized rod and frame test (CRAF), with a virtual line of t wo endpoints and a precision of 0.5°. All participants were right handed, with 31 in the normal t ime (NT) and 29 in the time pressure (TP) experimental conditions. Results showed that the feeling of act ing under time pressure induced rightward SVV adjustments (counter clockwise (CCW) SVV estimates) in the nontilted frame context and an increased rod and frame effect (RFE), but only significantly with a right tilt of the frame. This indicates an increased tendency for CCW SVV estimates and marked asymmetries in the magnitude of the frame effects for left and right frame tilt under time pressure. In view of these findings I believe that quick actions may provoke abnormal weighting of cues mediating verticality perception due to an asymmet rical processing of visual info rmation leading to an inefficient integration of sensory information in brain areas involved in SVV representation under time pressure. These findings may prove significant at a postural level for visually dependent individuals who may need to carry out postural orientation corrections quickly within environ ments rich with ob liquely oriented visual cues.
... Accordingly, the weight on a reference frame (modality) may need to be mod ified[24], because of changing environmental conditions, with this sensory reweighting process being critical for perceptuomotor control[3] and maintaining postural stability in a dynamic environment[6]. In particular, since it accurately represents the orientation of the environment, a stationary full field v isual stimu lus provides a useful reference therefore its associated weight will increase to improve postural stability[13, 15]. However, when static visual frames of reference are tilted, they can induce postural t ilt or sway in standing observers, because such visual cues conflict with other egocentric cues to spatial orientation[11], therefore, the weight assigned to the visual channel needs to be reduced in order to preserve balance. ...
Th is study tested the effects of perceived t ime pressure on subjective visual vertical (SVV) perception in co llege healthy male students. Delayed down-weighting of inaccurate visual cues has been imp licated in age-induced overreliance on visual informat ion, which may be disruptive for postural control. Accordingly, I hypothesized that under time pressure, participants may not have enough time to downgrade the distracting visual input fro m the tilted frame and display larger rod-and-frame effects (RFE) on a co mputerized rod and frame test (CRAF), with a virtual line of t wo endpoints and a precision of 0.5°. All participants were right handed, with 31 in the normal t ime (NT) and 29 in the time pressure (TP) experimental conditions. Results showed that the feeling of act ing under time pressure induced rightward SVV adjustments (counter clockwise (CCW) SVV estimates) in the nontilted frame context and an increased rod and frame effect (RFE), but only significantly with a right tilt of the frame. This indicates an increased tendency for CCW SVV estimates and marked asymmetries in the magnitude of the frame effects for left and right frame tilt under time pressure. In view of these findings I believe that quick actions may provoke abnormal weighting of cues mediating verticality perception due to an asymmet rical processing of visual info rmation leading to an inefficient integration of sensory information in brain areas involved in SVV representation under time pressure. These findings may prove significant at a postural level for visually dependent individuals who may need to carry out postural orientation corrections quickly within environ ments rich with ob liquely oriented visual cues.
... Elderly individuals and fallers exhibit greater postural sway than younger individuals and non-fallers, respectively, when vision is occluded or inaccurate (Whipple et al., 1993;Low Choy et al., 2003;Buatois et al., 2006). However, visual acuity also decreases with age, which could lead to overdependence on inaccurate visual information, and thus further decreases in postural stability and increases in fall risk (Lord et al., 2000;Jeka et al., 2006). ...
Background
Meniere’s disease (MD) is defined by episodic vertigo, unilateral sensorineural hearing loss and fluctuating aural symptoms. Due to the variable clinical presentation, objective tests of MD may have significant diagnostic utility. Head kinematics derived from a head-mounted display (HMD) have demonstrated to be sensitive to vestibular dysfunction. The purpose of this pilot study was to investigate whether head sway can differentiate between patients with MD, vestibular hypofunction (VH) and healthy controls.
Materials/methods
80 adults (30 healthy controls, 32 with VH, and 18 with MD) were recruited from a tertiary vestibular clinic. All underwent a postural control assessment using the HTC Vive Pro Eye HMD that recorded head sway in the anterior–posterior (AP), medio-lateral (ML), pitch, yaw and roll direction. Participants were tested with 2 levels of visual load: a static versus oscillating star display. Each scene lasted 60 s and was repeated twice. Sway in each direction was quantified using root mean square velocity (VRMS) for the first 20 s and full 60 s of each scene.
Results
Static visual: participants with VH showed significantly larger head VRMS than controls in the AP (60 s and 20 s) and pitch (20 s) directions. Dynamic visual: participants with VH showed significantly larger head VRMS than controls all directions for both the 60 and 20 s analysis. Participants with MD did not differ significantly from the control or the VH group.
Conclusion
While limited in numbers, Patients with MD had a high variability in head sway in all directions, and their average head sway was between controls and those with VH. A larger sample as well as patients with worse symptoms at time of testing could elucidate whether head sway via HMD could become a viable test in this population. A similar finding between 20- and 60-s scene and the full portability of the system with an in-clinic testing setup could help these future endeavors. Head sway derived from HMD is sensitive to VH and can be clinically useful as an outcome measure to evaluate sensory integration for postural control.
The human nervous system relies on sensory information from the feet and legs to control the way we balance and walk. However, even in healthy individuals this sensory information is inherently variable and clouded with uncertainty. Researchers have found that the central nervous system (CNS) estimates body position amid the uncertainty of sensory signals in a way consistent with Bayesian inference. Bayesian inference posits that the brain accounts for variability in sensory data by combining it with learned expectations built from previous movement attempts. While initial findings on this topic are promising, they have neglected to study full-body movements such as gait and balance. The purpose of this research was to determine if the CNS controls balance-related stepping tasks in a way that fits a Bayesian framework. To address this purpose, we created a virtual reality protocol where participants moved their center of mass (CoM) to various targets while relying on uncertain visual cues and compensating for an alternating shift to the cursor position. We showed that as incoming sensory information became less certain, participants relied more on their learned expectation of body position and demonstrated more uncertainty in their responses. Accordingly, as participants learned to control and estimate their CoM position during our mobility task, they relied both on the sensory information they were receiving as well as learned expectations for its location. These results provide further evidence that the CNS is aware of the variability in sensory information and is proficient at compensating for the resultant uncertainty. We aim to apply these findings as a method for measuring the efficacy of interventions targeting sensory function.
Exposure to postural threat has been documented to influence the sensory contributions of proprioceptive and vestibular information in standing balance control. Contributions from the visual system to balance are also crucial, yet the degree to which postural threat may modulate visual control of balance is not well characterized. Therefore, the aims of this study were to assess the feasibility of eliciting visual evoked postural responses (VEPRs) using head-mounted virtual reality (VR) and use this method to examine the potential influence of virtual postural threat on the visual control of balance. 36 healthy young adults were exposed to a pseudorandom, translational visual stimulus of a real-world environment in VR. The visual stimulus was presented in virtual conditions of LOW and HIGH postural threat in which participants stood at ground level, and on a 7m elevated platform, respectively. VEPRs were successfully produced in both postural threat conditions. When exposed to the visual stimulus while at an elevated surface height, participants demonstrated significant changes to their physiological arousal and emotional state. Despite significant coherence across the stimulus' frequency range, stimulus correlated VEPRs were not significantly modulated during exposure to the visual stimulus under virtual postural threat. This study supports the future utility of VR head-mounted displays in examining emotional influences on the visual control of balance.
This dissertation aimed to further our understanding of how increasing age affects gait and stability during gait in healthy adults. In addition, it also aimed to increase our understanding of how the loss of function of both balance portions of the inner ear (i.e., the vestibular apparatus) influences balance during standing and during gait. Increasing our knowledge on both topics could improve the effectiveness of the way elderly people and patients with a loss of function of the vestibular apparatus (i.e., bilateral vestibulopathy) are assessed. Doing so can in its turn help improve the identification of those people with an increased risk of falling.
Chapter 1 of this dissertation included a general introduction of the requirements of gait, together with how gait can be characterized. Additionally, it briefly described the different systems needed to control gait and how ageing and the loss of vestibular function can influence gait.
Chapter 2 of this dissertation examined the influence of an increasing age on the different characteristics of gait and on stability during gait. Chapter 2.1 reviewed the literature to examine the current knowledge on the differences of spatiotemporal characteristics of gait throughout the healthy adult life. The results indicated that most characteristics change with increasing age. Elderly populations showed a more cautious way of walking through slowing down and changing the time and distances covered by one step. It also showed that information on gait characteristics of middle-aged adults was missing. In Chapter 2.2 healthy adults between the ages of 20 to 89 were examined on spatiotemporal characteristics, the step-to-step variability, and the margins of stability to further our understanding of the influence of age on gait. Additionally, the interactions between the gait characteristics and the margins of stability were examined. Results of this chapter showed that older people change the way they walk by walking slower and taking shorter steps to increase their stability during walking. Older adults also show an increased variability in where they place their next step. As a result of these changes, older adults have a reduced ability to react to additional disturbances and could thus be more likely to experience a fall.
Chapter 3 of this dissertation examined the influence of a two-sided loss of function of the vestibular apparatus on gait. Patients with a bilateral vestibulopathy and healthy subjects of the same age were compared on spatiotemporal characteristics of gait and the step-to-step variability. In addition, the relationship between the gait characteristics and the margins of stability were investigated in both groups. Results of this chapter indicated that patients with bilateral vestibulopathy showed only limited differences in gait characteristics. However, they did show a different way to control stability during walking. Instead of changing the underlying gait characteristics, they relied more on the control of the accelerations of the centre of mass to improve stability during walking.
In Chapter 4 we examined the existing literature on the balance performance of patients with bilateral vestibulopathy and the way these were different compared to patients with a one-sided loss of vestibular function and healthy subjects. In conditions where visual information and somatosensory information is available, patients with bilateral vestibulopathy are able to perform on the same level as healthy subjects and unilateral vestibulopathy patients. It is only when both visual and somatosensory information is missing that bilateral vestibulopathy patients are unable to perform on the same level. Therefore, it was suggested to use balance assessments integrating missing or altered visual and somatosensory information during standing or walking to be able to thoroughly identify the balance problems in bilateral vestibulopathy.
Chapter 5 examined whether patients with bilateral vestibulopathy with a history of falls could be distinguished from those who did not fall. Different outcome measures related to the function of the vestibular apparatus, balance during standing and walking, questionnaires concerning self-perceived handicap, and characteristics of gait were examined. However, using these outcome measures, those patients with a history of falls could not be distinguished from those who did not fall. It is therefore suggested to investigate outcome measures assessing balance in challenging environments within the clinical setting, or to assess the patients during daily life itself.
The results of this dissertation, on the one hand, showed that with increasing age, the way we walk is adapted so stability is maintained. However, because of these changes, the remaining ability to adapt the way we walk in reaction to disturbances during walking decreases. On the other hand, results indicated that patients with bilateral vestibulopathy can perform on the same level as healthy controls whenever visual and somatosensory information is present. However, the way balance is controlled and stability is maintained may differ with healthy adults. Current evidence also illustrated that both patients with a history of falls and those without show an increased risk of falling, but that they cannot be distinguished from each other. Therefore, our current understanding of how balance and gait are altered in patients with bilateral vestibulopathy stresses the need to improve assessment protocols to identify those patients with an increased risk of falling.
The current study aimed to explore the impact of visual dependence on sensorimotor coupling of postural sway and visual motion in adults and teens with spastic cerebral palsy (CP). We hypothesized that individuals with CP would exhibit greater magnitudes of sway than healthy individuals, and the presence of visual dependence (VD) would produce instability in the direction of visual motion. Participants stood in a virtual environment in which the visual scene remained static or continuously rotated 30 degree/second in pitch-up or pitch-down. Increased center of pressure and center of mass responses were observed in the direction of visual scene motion in those with CP. Those with VD exhibited reduced frequency responses in anterior-posterior direction than those who were visually independent. VD suggests deficient sensorimotor integration that could contribute to postural instability and reduced motor function. Individuals with CP who are visually dependent may benefit from more sensory focused rehabilitation strategies.
Abbreviations: AP, anterior-posterior; CP, cerebral palsy; COM, center of mass; COP, center of pressure; MDF, median frequency; ML, mediolateral; PD, pitch down (nose down) rotation; PU, pitch up (nose up) rotation; RFT, rod and frame test; RMS, root mean square; SLP, slope of the fitted line; TD, typical development; VD, visual dependence; VI, visual independence; VOR, vestibulo-ocular reflex; VPI, visual perceptual impairment
Substantial advances in virtual reality (VR) technology open an exciting window towards better understanding of subdomains of balance control. Here we studied whether a portable VR headset can be used to test sensory integration for balance. Twenty young adults stood on a Both-Sides-Up (BOSU) ball or floor. Moving spheres were projected from an Oculus Development-Kit 2 at various amplitudes and frequencies. Participants gains' indicated visual 'weighting' when standing on BOSU but not on the floor and 're-weighting' with increased visual amplitude. Intraclass correlations showed acceptable to good reliability for all floor conditions and some of the BOSU conditions when we repeated the protocol a week later. Future steps to further develop our paradigm into a clinical assessment of sensory integration for postural control are discussed.
What happens at the sensory level when a person is balancing on compliant surfaces? Compliant surfaces such as Both-Sides-Up (BOSU) balls are often used as a form of 'proprioceptive exercises'. Clinical theories in neuro-rehabilitation suggest that compliant surfaces disrupt the somatosensory contribution to balance and increase reliance on vision and vestibular input. Understanding the sensory aspects of compliant surfaces exercises would have important implications for balance training of athletes and of people with somatosensory deficits, such as people with recurrent ankle sprains. We tested this clinical theory in a sample of 30 healthy young adults and 10 adults with history of repeated ankle sprains while standing on a BOSU ball, memory foam or floor. We measured participants' center of pressure response to dots projected on a screen, moving medio-laterally at one of 3 frequencies (0.4Hz, 0.48Hz and 0.56Hz). We calculated the magnitude of the postural response (gains), and participants' primary frequency (PF) of sway and compared it between surfaces per frequency. In both groups, gains were significantly higher on the BOSU compared to floor or foam (P<0.001) with no significant difference between floor and foam. The PF difference was significant (P<0.001) with a clear peak matching of the visual stimulation frequency only on the BOSU. During a single session of stance on compliant surfaces, visual dependence was a dominant factor on a challenging condition. When prescribing BOSU exercises to young adults as specific balance training, trainers should consider its effect on increased visual dependence with respect to that sessions' goals.
Multi-sensory re-weighting (MSR) is an adaptive process that prioritizes the visual, vestibular and somatosensory inputs that provide the most reliable information when environmental conditions change. This process is thought to degrade with increasing age, and to be particularly deficient in fall-prone versus healthy older adults. This dissertation presents three studies designed to investigate age-and fall-related changes in MSR. The first study examined the assumption of impaired MSR in healthy and fall-prone older adults using a two-frequency touch/vision experimental design with stimuli at varying amplitudes. Both healthy and fall-prone older adults demonstrated the same pattern of adaptive gain changes as healthy young adults. No group differences in the overall levels of vision and touch gain were found. These results suggest that, for small amplitude vision and touch stimuli, the central sensory re-weighting adaptation process remains intact in healthy and fall-prone older adults.
In this study, we explored whether gaze and posture would exhibit coordination with the motion of a presented visual stimulus, specifically with regard to the complexity of the motion structure. Fourteen healthy adults viewed a set of four visual stimulus motion conditions, in both self-selected and semi-tandem stance, during which the stimulus moved horizontally across a screen, with position updated to follow a sine, chaos, surrogate, or random noise trajectory. Posture was measured using a standard force platform in self-selected and semi-tandem stance conditions while gaze was recorded using image-based eye-tracking equipment. Cross-correlation confirmed the continuous coordination of gaze with each type of stimulus motion, with increasing lag as stimulus motion complexity increased. Correlation dimension and approximate entropy were used to assess the complexity of the measured gaze and posture behaviors, with these values compared against those of the actual stimulus via ANOVA and dependent t tests. We found that gaze behavior was particularly sensitive to the complexity of the stimulus motion, according to both metrics. Posture seemed to be unaffected by stimulus motion viewing; however, different stance conditions did exhibit differences in posture metrics. Our results support an evolving understanding of how vision is used for determining perception and action.
Research was carried out on the effects of aging and sensory motor defi cits following strokes with respect to the capacity of the central nervous system to resolve sensory confl icts created by Virtual Reality (VR). The results of this research demonstrate that VR can be a valuable tool for therapeutic interventions that require an adaptation to complex, multimodal environments. The rehabilitation protocols include balancing training in virtual environments. Les études qui ont été menées sur les effets du vieillissement et des défi cits sensori-moteurs consé-cutivement aux accidents vasculaires cérébraux concernent la capacité du système nerveux central à résoudre les confl its sensoriels créés par la Réalité Virtuelle (RV). Les résultats de ces études ont démontré que la RV peut être un instrument valable en tant qu'intervention thérapeutique ce qui requiert l'adaptation aux environnements multimodaux complexes. Les protocoles de réédu-cation comportent des exercices d'équilibration dans les environnements virtuels.
Patients whose deficits were limited to clinically well qualified vestibular disorders have been exposed to a number of altered support surface and visual environments while standing unsupported. A six- degrees-of-freedom platform employing movable support surfaces for each foot and a movable visual surround deprived patients of normal inputs derived from a fixed level support surface and from an immobile surround. Various tests employing EMG, force, and body movement recording identified quantitative changes in the patients' strategy for the relative weighting of proprioceptive, vestibular, and visual inputs. The most dramatic performance deficit of patients was their inability to suppress the influence of visual and proprioceptive inputs appropriately whenever motions of external surface disturbed the orientation information provided by these inputs. Thus, the more mildly afflicted patients experienced instability not so much because of the loss of vestibular inputs directly to posture but because of their inappropriate responses to proprioceptive inputs and vision. Discussion is centered on the role of vestibular input as an internal reference system for orientation about which adaptive changes in proprioceptive and visual inputs are made.
Two experiments were designed to investigate the use of optical flow for postural control as a function of its velocity, geometry,
and retinal placement. In the first experiment, subjects were exposed to a room that moved at a velocity below the reported
threshold for detection of point-light motion. In the second, the room was moved so that optical velocities were above this
threshold. Compensatory sway was assessed for both lamellar and radial flow to central and peripheral areas of the retina.
Compensatory sway was elicited with optical velocities below the point-light motion threshold, suggesting that this threshold
is not relevant to the detection of egomotion. The results also indicate that the retinal periphery does not detect posture-relevant
information from flow fields with a radial dynamic structure. Since the higher velocities used in the second experiment exceeded
those generated by natural postural instabilities, it was concluded that radial flow in the retinal periphery is not used
as a source of information for normal postural maintenance, and therefore that flow structure is an important factor in the
detection and control of egomotion.
When standing human subjects are exposed to a moving visual environment, the induced postural sway displays varying degrees of coherence with the visual information. In our experiment we varied the frequency of an oscillatory visual display and analysed the temporal relationship between visual motion and sway. We found that subjects maintain sizeable sway amplitudes even as temporal coherence with the display is lost. Postural sway tended to phase lead (for frequencies below 0.2 Hz) or phase lag (above 0.3 Hz). However, we also observed at a fixed frequency, highly variable phase relationships in which a preferred range of phase lags is prevalent, but phase jumps occur that return the system into the preferred range after phase has begun drifting out of the preferred regime. By comparing the results quantitatively with a dynamical model (the sine-circle map), we show that this effect can be understood as a form of relative coordination and arises through an instability of the dynamics of the action-perception cycle. Because such instabilities cannot arise in passively driven systems, we conclude that postural sway in this situation is actively generated as rhythmic movement which is coupled dynamically to the visual motion.
The concept of a generalized aging effect on a generalized balance mechanism is discussed, and an alternative, multicomponent approach to understanding the heterogeneity of postural dyscontrol in the elderly is presented. Neural sensorimotor components of normal postural control mechanisms are identified and discussed. The effects of Parkinson's disease, hemiplegia, cerebellar degeneration, peripheral vestibular loss, and other disorders on the components of postural control are summarized. Quantitative posturography is advocated to detect preclinical manifestation of multiple musculoskeletal and neuromuscular pathologies and reduced compensatory abilities in posturally unstable elderly adults.
Patients whose deficits were limited to clinically well qualified vestibular disorders have been exposed to a number of altered support surface and visual environments while standing unsupported. A six-degrees-of-freedom platform employing movable support surfaces for each foot and a movable visual surround deprived patients of normal inputs derived from a fixed level support surface and from an immobile surround. Various tests employing EMG, force, and body movement recording identified quantitative changes in the patients' strategy for the relative weighting of proprioceptive, vestibular, and visual inputs. The most dramatic performance deficit of patients was their inability to suppress the influence of visual and proprioceptive inputs appropriately whenever motions of external surface disturbed the orientation information provided by these inputs. Thus, the more mildly afflicted patients experienced instability not so much because of the loss of vestibular inputs directly to posture but because of their inappropriate responses to proprioceptive inputs and vision. Discussion is centered on the role of vestibular input as an internal reference system for orientation about which adaptive changes in proprioceptive and visual inputs are made.
When standing human subjects are exposed to a moving visual environment, the induced postural sway displays varying degrees of coherence with the visual information. In our experiment we varied the frequency of an oscillatory visual display and analysed the temporal relationship between visual motion and sway. We found that subjects maintain sizeable sway amplitudes even as temporal coherence with the display is lost. Postural sway tended to phase lead (for frequencies below 0.2 Hz) or phase lag (above 0.3 Hz). However, we also observed at a fixed frequency, highly variable phase relationships in which a preferred range of phase lags is prevalent, but phase jumps occur that return the system into the preferred range after phase has begun drifting out of the preferred regime. By comparing the results quantitatively with a dynamical model (the sine-circle map), we show that this effect can be understood as a form of relative coordination and arises through an instability of the dynamics of the action-perception cycle. Because such instabilities cannot arise in passively driven systems, we conclude that postural sway in this situation is actively generated as rhythmic movement which is coupled dynamically to the visual motion.
When standing human subjects are exposed to a moving visual environment, the induced postural sway forms a stable temporal relationship with the visual information. We have investigated this relationship experimentally with a new set-up in which a computer generates video images which correspond to the motion of a 3D environment. The suggested mean distance to a sinusoidally moving wall is varied and the temporal relationship to induced sway is analysed (1) in terms of the fluctuations of relative phase between visual and sway motion and (2) in terms of the relaxation time of relative phase as determined from the rate of recovery of the stable relative phase pattern following abrupt changes in the visual motion pattern. The two measures are found to converge to a well-defined temporal stability of the action-perception cycle. Furthermore, we show that this temporal stability is a sensitive measure of the strength of the action-perception coupling. It decreases as the distance of the visual scene from the observer increases. This fact and the increase of mean relative phase are consistent with predictions of a linear second-order system driven by the visual expansion rate. However, the amplitude of visual sway decreases little as visual distance increases, in contradiction to the predictions, and is suggestive of a process that actively generates sway. The visual expansion rate on the optic array is found to decrease strongly with visual distance. This leads to the conclusion that postural control in a moving visual environment cannot be understood simply in terms of minimization of retinal slip, and that dynamic coupling of vision into the postural control system must be taken into account.
This study tested balance behavior of young adults and aging adults with and without balance problems in response to visual flow from a moving visual surround.
Balance behavior was indexed by force plate measures of maximum anterior/posterior displacement of the center of foot pressure and horizontal shear forces. The sample included normal young adults (n = 13; mean age 23 years, +/- 7.5), normal aging adults (n = 13; mean age 76 years, +/- 6.5), and aging adults with balance problems not directly attributable to a diagnosable neurological disease or dysfunction (n = 13; mean age 79 years, +/- 5.8).
The balance-affected aging group had statistically greater sway responses than the young group when the stimulus was unexpected (as in the first trial; p < .05). Some individuals in each group had large responses that were statistical outliers from the group median. The balance-affected group had significantly greater shear forces than the young group.
Greater sway responses suggest over-reliance on visual cues for posture control in the balance-affected aging group, which may be related to underlying, borderline somatosensory deficits, as indicated by the patterns of subclinical indications for somatosensory impairments on neurological exams in this group. Visually sensitive postural control, however, may issue from several different underlying processes. Elevated shear forces during balance responses in the balance-affected group suggest a greater use of hip movements in addition to ankle movements for postural adjustments.
When we make saccadic eye movements or goal-directed arm movements, there is an infinite number of possible trajectories that the eye or arm could take to reach the target. However, humans show highly stereotyped trajectories in which velocity profiles of both the eye and hand are smooth and symmetric for brief movements. Here we present a unifying theory of eye and arm movements based on the single physiological assumption that the neural control signals are corrupted by noise whose variance increases with the size of the control signal. We propose that in the presence of such signal-dependent noise, the shape of a trajectory is selected to minimize the variance of the final eye or arm position. This minimum-variance theory accurately predicts the trajectories of both saccades and arm movements and the speed-accuracy trade-off described by Fitt's law. These profiles are robust to changes in the dynamics of the eye or arm, as found empirically. Moreover, the relation between path curvature and hand velocity during drawing movements reproduces the empirical 'two-thirds power law. This theory provides a simple and powerful unifying perspective for both eye and arm movement control.
We analyze the stochastic structure of postural sway and demonstrate that this structure imposes important constraints on models of postural control. Linear stochastic models of various orders were fit to the center-of-mass trajectories of subjects during quiet stance in four sensory conditions: (i) light touch and vision, (ii) light touch, (iii) vision, and (iv) neither touch nor vision. For each subject and condition, the model of appropriate order was determined, and this model was characterized by the eigenvalues and coefficients of its autocovariance function. In most cases, postural-sway trajectories were similar to those produced by a third-order model with eigenvalues corresponding to a slow first-order decay plus a faster-decaying damped oscillation. The slow-decay fraction, which we define as the slow-decay autocovariance coefficient divided by the total variance, was usually near 1. We compare the stochastic structure of our data to two linear control-theory models: (i) a proportional-integral-derivative control model in which the postural system's state is assumed to be known, and (ii) an optimal-control model in which the system's state is estimated based on noisy multisensory information using a Kalman filter. Under certain assumptions, both models have eigenvalues consistent with our results. However, the slow-decay fraction predicted by both models is less than we observe. We show that our results are more consistent with a modification of the optimal-control model in which noise is added to the computations performed by the state estimator. This modified model has a slow-decay fraction near 1 in a parameter regime in which sensory information related to the body's velocity is more accurate than sensory information related to position and acceleration. These findings suggest that: (i) computation noise is responsible for much of the variance observed in postural sway, and (ii) the postural control system under the conditions tested resides in the regime of accurate velocity information.
In literature, it has been suggested that the CNS anticipates spontaneous change in body position during quiet stance and continuously modulates ankle extensor muscle activity to compensate for the change. The purpose of this study was to investigate whether velocity feedback contributes by modulating ankle extensor activities in an anticipatory fashion, facilitating effective control of quiet stance. Both theoretical analysis and experiments were carried out to investigate to what extent velocity feedback contributes to controlling quiet stance. The experiments were carried out with 16 healthy subjects who were asked to stand quietly with their eyes open or closed. During the experiments, the center of pressure (COP) displacement (COPdis), the center of mass (COM) displacement (COMdis), and COM velocity (COMvel) in the anteroposterior direction were measured. Rectified electromyograms (EMGs) were used to measure muscle activity in the right soleus muscle, the medial gastrocnemius muscle, and the lateral gastrocnemius muscle. The simulations were performed using an inverted pendulum model that described the anteroposterior kinematics and dynamics of quiet stance. In the simulations, an assumption was made that the COMdis of the body would be regulated using a proportional-derivative (PD) controller. Two different PD controllers were evaluated in these simulations: 1) a controller with the high-derivative/velocity gain (HDG) and 2) a controller with the low-derivative/velocity gain (LDG). Cross-correlation analysis was applied to investigate the relationships between time series obtained in experiments 1) COMdis and EMGs and 2) COMvel and EMGs. Identical cross-correlation analysis was applied to investigate the relationships between time series obtained in simulations 3) COMdis and ankle torque and 4) COMvel and ankle torque. The results of these analyses showed that the COMdis was positively correlated with all three EMGs and that the EMGs temporally preceded the COMdis. These findings agree with the previously published studies in which it was shown that the lateral gastrocnemius muscle is actively modulated in anticipation of the body's COM position change. The COMvel and all three EMGs were also correlated and the cross-correlation function (CCF) had two peaks: one that was positive and another that was negative. The positive peaks were statistically significant, unlike the negative ones; they were larger than the negative peaks; and their time shifts were much shorter compared with the time shifts of the negative peaks. When these results were compared with the CCF results obtained for simulated time series, it was discovered that the cross-correlation results for the HDG controller closely matched cross-correlation results for the experimental time series. On the other hand, the simulation result obtained for LDG controller did not match the experimental results. These findings suggest that the actual postural control system during quiet stance adopts a control strategy that relies notably on velocity information and that such a controller can modulate muscle activity in anticipatory manner without using a feed-forward mechanism.
The problem of how the nervous system fuses sensory information from multiple modalities for upright stance control remains largely unsolved. It is well established that the visual, vestibular, and somatosensory modalities provide position and rate (e.g., velocity, acceleration) information for estimation of body dynamics. However, it is unknown whether any particular property dominates when multisensory information is fused. Our recent stochastic analysis of postural sway during quiet stance suggested that sensory input provides more accurate information about the body's velocity than its position or acceleration. Here we tested this prediction by degrading major sources of velocity information through removal/attenuation of sensory information from vision and proprioception. Experimental measures of postural sway were compared with model predictions to determine whether sway behavior was indicative of a deficit in velocity information rather than position or acceleration information. Subjects stood with eyes closed on a support surface that was 1) fixed, 2) foam, or 3) sway-referenced. Six measures characterizing the stochastic structure of postural sway behaved in a manner consistent with model predictions of degraded velocity information. Results were inconsistent with the effect of degrading only position or acceleration information. These findings support the hypothesis that velocity information is the most accurate form of sensory information used to stabilize posture during quiet stance. Our results are consistent with the assumption that changes in sway behavior resulting from commonly used experimental manipulations (e.g., foam, sway-referencing, eyes closed) are primarily attributed to loss of accurate velocity information.
It is well known that the human postural control system responds to motion of the visual scene, but the implicit assumptions it makes about the visual environment and what quantities, if any, it estimates about the visual environment are unknown. This study compares the behavior of four models of the human postural control system to experimental data. Three include internal models that estimate the state of the visual environment, implicitly assuming its dynamics to be that of a linear stochastic process (respectively, a random walk, a general first-order process, and a general second-order process). In each case, all of the coefficients that describe the process are estimated by an adaptive scheme based on maximum likelihood. The fourth model does not estimate the state of the visual environment. It adjusts sensory weights to minimize the mean square of the control signal without making any specific assumptions about the dynamic properties of the environmental motion.
We find that both having an internal model of the visual environment and its type make a significant difference in how the postural system responds to motion of the visual scene. Notably, the second-order process model outperforms the human postural system in its response to sinusoidal stimulation. Specifically, the second-order process model can correctly identify the frequency of the stimulus and completely compensate so that the motion of the visual scene has no effect on sway. In this case the postural control system extracts the same information from the visual modality as it does when the visual scene is stationary. The fourth model that does not simulate the motion of the visual environment is the only one that reproduces the experimentally observed result that, across different frequencies of sinusoidal stimulation, the gain with respect to the stimulus drops as the amplitude of the stimulus increases but the phase remains roughly constant. Our results suggest that the human postural control system does not estimate the state of the visual environment to respond to sinusoidal stimuli.
It is generally accepted that human bipedal upright stance is achieved by feedback mechanisms that generate an appropriate corrective torque based on body-sway motion detected primarily by visual, vestibular, and proprioceptive sensory systems. Because orientation information from the various senses is not always available (eyes closed) or accurate (compliant support surface), the postural control system must somehow adjust to maintain stance in a wide variety of environmental conditions. This is the sensorimotor integration problem that we investigated by evoking anterior-posterior (AP) body sway using pseudorandom rotation of the visual surround and/or support surface (amplitudes 0.5–8°) in both normal subjects and subjects with severe bilateral vestibular loss (VL). AP rotation of body center-of-mass (COM) was measured in response to six conditions offering different combinations of available sensory information. Stimulus-response data were analyzed using spectral analysis to compute transfer functions and coherence functions over a frequency range from 0.017 to 2.23 Hz. Stimulus-response data were quite linear for any given condition and amplitude. However, overall behavior in normal subjects was nonlinear because gain decreased and phase functions sometimes changed with increasing stimulus amplitude. “Sensory channel reweighting” could account for this nonlinear behavior with subjects showing increasing reliance on vestibular cues as stimulus amplitudes increased. VL subjects could not perform this reweighting, and their stimulus-response behavior remained quite linear. Transfer function curve fits based on a simple feedback control model provided estimates of postural stiffness, damping, and feedback time delay. There were only small changes in these parameters with increasing visual stimulus amplitude. However, stiffness increased as much as 60% with increasing support surface amplitude. To maintain postural stability and avoid resonant behavior, an increase in stiffness should be accompanied by a corresponding increase in damping. Increased damping was achieved primarily by decreasing the apparent time delay of feedback control rather than by changing the damping coefficient (i.e., corrective torque related to body-sway velocity). In normal subjects, stiffness and damping were highly correlated with body mass and moment of inertia, with stiffness always about 1/3 larger than necessary to resist the destabilizing torque due to gravity. The stiffness parameter in some VL subjects was larger compared with normal subjects, suggesting that they may use increased stiffness to help compensate for their loss. Overall results show that the simple act of standing quietly depends on a remarkably complex sensorimotor control system.
It is generally accepted that human bipedal upright stance is achieved by feedback mechanisms that generate an appropriate corrective torque based on body-sway motion detected primarily by visual, vestibular, and proprioceptive sensory systems. Because orientation information from the various senses is not always available (eyes closed) or accurate (compliant support surface), the postural control system must somehow adjust to maintain stance in a wide variety of environmental conditions. This is the sensorimotor integration problem that we investigated by evoking anterior-posterior (AP) body sway using pseudorandom rotation of the visual surround and/or support surface (amplitudes 0.5-8degrees) in both normal subjects and subjects with severe bilateral vestibular loss (VL). AP rotation of body center-of-mass (COM) was measured in response to six conditions offering different combinations of available sensory information. Stimulus-response data were analyzed using spectral analysis to compute transfer functions and coherence functions over a frequency range from 0.017 to 2.23 Hz. Stimulus-response data were quite linear for any given condition and amplitude. However, overall behavior in normal subjects was nonlinear because gain decreased and phase functions sometimes changed with increasing stimulus amplitude. "Sensory channel reweighting" could account for this nonlinear behavior with subjects showing increasing reliance on vestibular cues as stimulus amplitudes increased. VL subjects could not perform this reweighting, and their stimulus-response behavior remained quite linear. Transfer function curve fits based on a simple feedback control model provided estimates of postural stiffness, damping, and feedback time delay. There were only small changes in these parameters with increasing visual stimulus amplitude. However, stiffness increased as much as 60% with increasing support surface amplitude. To maintain postural stability and avoid resonant behavior, an increase in stiffness should be accompanied by a corresponding increase in damping. Increased damping was achieved primarily by decreasing the apparent time delay of feedback control rather than by changing the damping coefficient (i.e., corrective torque related to body-sway velocity). In normal subjects, stiffness and damping were highly correlated with body mass and moment of inertia, with stiffness always about 1/3 larger than necessary to resist the destabilizing torque due to gravity. The stiffness parameter in some VL subjects was larger compared with normal subjects, suggesting that they may use increased stiffness to help compensate for their loss. Overall results show that the simple act of standing quietly depends on a remarkably complex sensorimotor control system.
A practical and accessible introduction to numerical methods for stochastic differential equations is given. The reader is assumed to be familiar with Euler's method for deterministic differential equations and to have at least an intuitive feel for the concept of a random variable; however, no knowledge of advanced probability theory or stochastic processes is assumed. The article is built around 10 MATLAB programs, and the topics covered include stochastic integration, the Euler-Maruyama method, Milstein's method, strong and weak convergence, linear stability, and the stochastic chain rule.
Despite extensive research on the influence of visual, vestibular and somatosensory information on human postural control,
it remains unclear how these sensory channels are fused for self-orientation. The focus of the present study was to test whether
a linear additive model could account for the fusion of touch and vision for postural control. We simultaneously manipulated
visual and somatosensory (touch) stimuli in five conditions of single- and multisensory stimulation. The visual stimulus was
a display of random dots projected onto a screen in front of the standing subject. The somatosensory stimulus was a rigid
plate which subjects contacted lightly (<1N of force) with their right index fingertip. In each condition, one sensory stimulus
oscillated (dynamic) in the medial-lateral direction while the other stimulus was either dynamic, static or absent. The results
qualitatively supported five predictions of the linear additive model in that the patterns of gain and variability across
conditions were consistent with model predictions. However, a strict quantitative comparison revealed significant deviations
from model predictions, indicating that the sensory fusion process clearly has nonlinear aspects. We suggest that the sensory
fusion process behaved in an approximately linear fashion because the experimental paradigm tested postural control very close
to the equilibrium point of vertical upright.
The classic book on human movement in biomechanics, newly updated. Widely used and referenced, David Winter's Biomechanics and Motor Control of Human Movement is a classic examination of techniques used to measure and analyze all body movements as mechanical systems, including such everyday movements as walking. It fills the gap in human movement science area where modern science and technology are integrated with anatomy, muscle physiology, and electromyography to assess and understand human movement. In light of the explosive growth of the field, this new edition updates and enhances the text with: Expanded coverage of 3D kinematics and kinetics. New materials on biomechanical movement synergies and signal processing, including auto and cross correlation, frequency analysis, analog and digital filtering, and ensemble averaging techniques. Presentation of a wide spectrum of measurement and analysis techniques. Updates to all existing chapters. Basic physical and physiological principles in capsule form for quick reference. An essential resource for researchers and student in kinesiology, bioengineering (rehabilitation engineering), physical education, ergonomics, and physical and occupational therapy, this text will also provide valuable to professionals in orthopedics, muscle physiology, and rehabilitation medicine. In response to many requests, the extensive numerical tables contained in Appendix A: "Kinematic, Kinetic, and Energy Data" can also be found at the following Web site: www.wiley.com/go/biomechanics.
Vision and/or ankle somatosensory inputs often do not correlate with the position of the center of gravity. In this case, visual or somatosensory information may be in conflict with other sensory systems that convey a true sense of body orientation. The purpose of this study was to determine how conflicting visual and ankle somatosensory inputs influenced standing balance in elders with a history of falls. Forty-seven community-dwelling elders (8 male, 39 female), between 65 and 96 years of age (mean = 80.5, SD = 9.0), participated in this project. Subjects with two or more falls in the 6 months prior to study were assigned to a fall group (n = 16), whereas those with no history of falling during the same time interval were assigned to a no-fall group (n = 31). In order to remove any bias in the testing procedure, the tester was not aware of group assignments. Subjects were evaluated using a sensory organization test (SOT) for standing balance and a "Get Up and Go" test (GUGT) for general mobility. Analysis of covariance was used to evaluate the SOT scores (by group, vision, and surface condition) and the GUGT scores. Body sway is known to increase with the normal aging process, and for this reason, age was selected as a covariate. The association between the SOT total score and the GUGT score was evaluated using Spearman rank-order correlation coefficients. The results showed a significant interaction between group and surface conditions, which indicated a decreased stance duration for fallers on a compliant surface compared with the stance duration for nonfallers (adjusted mean faller stance duration = 53 seconds, SD = 42; mean nonfaller stance duration = 67 seconds, SD = 32). Subjects in the fall group also had significantly higher GUGT scores (which indicated poor mobility function) than did subjects in the nonfall group (adjusted mean faller GUGT score = 2.65, SD = 1.48; mean nonfaller GUGT score = 1.47, SD = 0.77). The Spearman correlation between total SOT scores and the GUGT scores was greater for fallers (r = -.67) than for nonfallers (r = -.44). Orientation input from the ankle appears to have greater importance for preventing falls compared with a visual reference. The SOT and GUGT may be useful in the field to establish criteria for screening elders in a fall-prevention program.
One of the most pervasive findings in the literature on the aged is the general slowing of cognitive-motor responses with advancing age. Hence, an increased slowness in the processing of information from vestibular, visual, and somatosensory systems could contribute greatly to a decline in postural stability. To examine this question, in a cross-sectional investigation, postural sway behavior of elderly (n = 18) and young (n = 10) adults was examined under conditions that stressed the slower integrative mechanisms rather than the reflexive mechanisms of postural control. The postural sway behavior of young and elderly subjects was examined for a prolonged duration (80 s), under altered visual and/or support surface (5 cm thick foam surface) conditions, and contrasted with normal stance. Results showed that the exclusion or disruption of one of the sensory inputs, alone, was not consistently sufficient to differentiate between elderly and young adults, because of compensation by the remaining sensory sources. Both alterations together (i.e., visual and surface), however, had a substantially greater effect upon the elderly than the young.
The development of a systematic approach to the diagnosis and management of ataxias of vestibular origin depends critically on the elucidation of the complex sensory and motor interactions involved in human postural control. In this paper, the results of studies of both sensory and motor control of posture in adults and children with peripheral vestibular deficits are summarized and reviewed. In studies of the sensory organization of postural control, normal subjects and patients with peripheral vestibular deficits were exposed to unreliable information from their support surface and/or visual surround during quiet stance. While normal adults and children were able to maintain balance under these conditions, the majority of children and adults with peripheral vestibular deficits showed one or both of the following abnormalities: (1)Vestibular loss patients were unable to maintain equilibrium when forced to rely on vestibular information for postural control. (2)Vestibular distortion patients were unable to select an accurate source of sensory information when exposed to sensory conflicts during quiet stance. Preliminary results of studies of motor coordination in these patients also suggest that vestibular loss patients rely almost exclusively on ankle sway to control posture, even during balance tasks which require hip movements to maintain equilibrium. In contrast, some vestibular distortion patients appear to rely on hip motions, even when not required to do so to maintain balance. The results of these studies are discussed in terms of the implications for both sensory and motor aspects of postural control in patients with ataxias of vestibular origin.
The following study examined two aspects of balance control in the older adult: the coordination of the timing and the amplitude of muscle responses to postural perturbations, and the ability of the participant to reorganize sensory inputs and subsequently modify postural responses as a consequence of changing environmental conditions. Coordination of muscle activity in postural responses of twelve elderly (sixty-one to seventy-eight years) participants were compared to those of young (nineteen to thirty-eight years) adults using a movable platform and recording the electromyographic activity of muscles of the legs. The following changes were noted in the timing and amplitude of muscle activity within a postural response synergy: increases in the absolute latency of distal muscle responses were observed in all older adults; in five of the twelve older adults temporal reversals of proximal and distal muscle response onset were observed; and there was a breakdown in the correlation of the amplitude of responses within a synergy. The ability of the older adult to balance under conditions of reduced or conflicting sensory information was also impaired. When confronted with functionally inappropriate visual and/or somatosensory inputs, half of the older group lost balance. In most instances, however, the older participants were able to maintain stability during subsequent responses to conflicting stimuli.
Neuromuscular function, which underlies efficient gait and balance, deteriorates with age and disease. A review of the literature and of data from the current study suggests the presence of poor gait and balance in elderly individuals who have a history of multiple falls. The tests of gait and balance are simple to perform and therefore may be widely applicable in evaluating individuals at risk of falls. Quantitative studies of motor and sensory function, vibratory sensation, and electrophysiologic studies of nerve integrity are discussed. Deteriorating motor and sensory control mechanisms appear to play an important role in falling.
Assessment of postural control in vestibular deficient subjects with and without visual and ankle joint sway information permitted: 1) a quantitative assessment of the overall vestibular information used by the individual patient for control of upright posture; 2) an estimate of the extent to which the vestibular deficient subject can appropriately "select" and alternatively use visual and ankle joint somatosensory information for compensatory postural control and 3) quantification of adaptive changes in postural responses to visual and somatosensory inputs. Results from this study support the hypothesis that abnormal vestibular function disrupts the subject's reference to gravity (earth) vertical. This loss of an absolute spatial reference normally provided by vestibular input prevents the resolution of conflicting or inaccurate visual and somatosensory spatial references which may occur during active or passive body movements.
The purpose of this study was to determine the contribution of visual, vestibular, and somatosensory cues to the maintenance of stance in humans. Postural sway was induced by full-field, sinusoidal visual surround rotations about an axis at the level of the ankle joints. The influences of vestibular and somatosensory cues were characterized by comparing postural sway in normal and bilateral vestibular absent subjects in conditions that provided either accurate or inaccurate somatosensory orientation information. In normal subjects, the amplitude of visually induced sway reached a saturation level as stimulus amplitude increased. The saturation amplitude decreased with increasing stimulus frequency. No saturation phenomena were observed in subjects with vestibular loss, implying that vestibular cues were responsible for the saturation phenomenon. For visually induced sways below the saturation level, the stimulus-response curves for both normal subjects and subjects experiencing vestibular loss were nearly identical, implying (1) that normal subjects were not using vestibular information to attenuate their visually induced sway, possibly because sway was below a vestibular-related threshold level, and (2) that subjects with vestibular loss did not utilize visual cues to a greater extent than normal subjects; that is, a fundamental change in visual system "gain" was not used to compensate for a vestibular deficit. An unexpected finding was that the amplitude of body sway induced by visual surround motion could be almost 3 times greater than the amplitude of the visual stimulus in normal subjects and subjects with vestibular loss. This occurred in conditions where somatosensory cues were inaccurate and at low stimulus amplitudes. A control system model of visually induced postural sway was developed to explain this finding. For both subject groups, the amplitude of visually induced sway was smaller by a factor of about 4 in tests where somatosensory cues provided accurate versus inaccurate orientation information. This implied (1) that the subjects experiencing vestibular loss did not utilize somatosensory cues to a greater extent than normal subjects; that is, changes in somatosensory system "gain" were not used to compensate for a vestibular deficit, and (2) that the threshold for the use of vestibular cues in normal subjects was apparently lower in test conditions where somatosensory cues were providing accurate orientation information.
Stabliographic techniques were used to better understand the role of the visual system in the perceptual motor activity of older people as it relates to the maintenance of postural control. The central research question was to determine the sensitivity of the subject's visual system to changes in three standard conditions of optical flow generated by an experimental moving room. Any movement that was present as a function of this optical flow field was recorded on a force platform and expressed in movement of a computed center-of-pressure variable. Movement of the center of pressure was recorded in a baseline condition and in the experimental conditions, and the data were analyzed with respect to differences in the three conditions of optical flow and between both younger and older subjects. The older subject group exhibited less stability than the younger subjects in response to the baseline conditions; and, after adjusting for baseline movement, the center-of-pressure motions of younger and older subjects, in response to the experimental conditions, were compared. No reliable differences were present between younger and older subjects for the radial optical flow condition; in the lamellar flow condition, older subjects moved significantly more than younger subjects; and, in the combined condition (global), the movement of the older subjects was significantly greater than that of the younger subjects for all motion variables recorded. The results are interpreted and discussed both in terms of their implication for falling in the elderly and in the context of an ecological interpretation of the role of vision in maintaining postural stability while both stationary and in motion.
To determine which measurements and test conditions on posturography are most useful for identifying balance problems in older people.
Two samples of 70 community-dwelling older subjects (> 75 years). One group (controls) considered their balance normal for their age, and the other (patients) complained of imbalance.
Velocity of sway on static (with and without foam) and dynamic posturography, Tinetti gait and balance score, self-reported fear of falling, and number and circumstances of falls.
Mean sway velocity was significantly increased in patients compared with controls. The greatest difference between patients and controls occurred with measures of anterior-posterior sway velocity during angular tilt of the platform. Sway velocity was not significantly increased in patients or controls who reported falls compared with those who did not report falls. Even when comparing those who fell as a result of loss of balance with those who fell because of trips or slips, there was no significant difference in sway velocity. By contrast, those who reported fear of falling (patients and controls) had significantly increased sway velocity compared with those who did not report fear of falling.
On average, velocity of sway (particularly in the anterior-posterior direction) is higher in older subjects who complain of imbalance compared with age-matched controls, and the difference is greater with dynamic posturography than with static posturography. However, the posturography data provided little information about the cause of the imbalance and did not correlate with the frequency of reported falls.