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Optimal Control Strategies Under Different Feedback Schedules: Kinematic Evidence
Abstract
Two experiments were conducted in which participants (N = 12, Experiment 1; N = 12, Experiment 2) performed rapid aiming movements with and without visual feedback under blocked, random, and alternating feedback schedules. Prior knowledge of whether vision would be available had a significant impact on the strategies that participants adopted. When they knew that vision would be available, less time was spent preparing movements before movement initiation. Participants also reached peak deceleration sooner but spent more time after peak deceleration adjusting limb trajectories. Consistent with those findings, analysis of spatial variability at different points in the trajectory indicated that variability increased up to peak deceleration but then decreased from peak deceleration to the end of the movement.
... For example, it has been shown that individuals tend to prolong their reaction times, which may indicate some refinement of the initial pre-programming of the movement (Hansen, Glazebrook, Anson, Weeks, & Elliott, 2006). In addition, participants tend to reduce their force-output, and consequently within-participant spatial variability, which may partially compensate for the lack of visually-regulated online corrections toward the end of the movement (Elliott, Chua, Pollock, & Lyons, 1995;Khan, Elliott, Coull, Chua, & Lyons, 2002). This is consistent with a decrease in the relative time after peak velocity, which is where these online corrections usually occur. ...
... Movement onset was determined as the first moment when the velocity reached ≥20 mm/s, while movement offset was determined as the subsequent moment when velocity reached between <10 mm/s and > − 10 mm/s. This criteria was broadly consistent with previous studies (e.g., Hansen et al., 2006;Khan et al., 2002;Robinson, Elliott, Hayes, Barton, & Bennett, 2014), while the shift toward a minimum negative velocity at offset captures the potential for zero-crossings near the endpoint (e.g., Dounskaia, Wisleder, & Johnson, 2005;Elliott et al., 2014;Fradet, Lee, & Dounskaia, 2008;Hsieh, Liu, & Newell, 2017). ...
... It is well known that aiming in the absence of visual feedback usually causes individuals to prolong their reaction time, increase (decrease) the proportion of time to (after) peak velocity and decrease the spatial variability within the initial trajectory (Hansen et al., 2006;see also, Elliott et al., 1995;Khan et al., 2002). These changes are suggested to manifest from attempts to refine the initial preprogramming and limit the subsequent error within the movement, which can then partially off-set the inability to undertake visuallyregulated online control. ...
The accuracy and precision of target-directed aiming is contingent upon the availability of online visual feedback. The present study aimed to examine the visual regulation of aiming with blurred vision. The aiming task was executed using a stylus on a graphics digitizing board, which was translated onto a screen in the form of a cursor (representing the moving limb) and target. The vision conditions involved the complete disappearance or blur of the cursor alone, target alone, and cursor+target. These conditions involved leaving the screen uncovered or covering with a diffusing sheet to induce blur. The distance between the screen and sheet was increased to make the blur progressively more severe (0 cm, 3 cm). Results showed significantly less radial and variable error under blurred compared to no vision of the cursor and cursor+target. These findings were corroborated by the movement kinematics including a shorter proportion of time to peak velocity, more negative within-participant correlation between the distances travelled to and after peak velocity, and lower spatial variability from peak velocity to the end of the movement under blurred vision. The superior accuracy and precision under the blurred compared to no vision conditions is consistent with functioning visual regulation of aiming, which is primarily contingent upon the online visual feedback of the moving limb. This outcome may be attributed to the processing of low spatial-high temporal frequencies. Potential implications for low vision diagnostics are discussed.
... Il est intéressant de souligner que les résultats actuels en dénomination d'images sur les temps de préparation sont inversés par rapport à ceux rapportés dans la littérature lors de la production de séquences de lettres (van Doorn & Keuss, 1992). En l'absence de feedback visuel, les rédacteurs prennent probablement plus de temps pour planifier les mouvements requis pour produire une séquence de lettres, car ils anticipent leur impossibilité d'ajuster en temps réel leurs mouvements (Khan et al., 2002 pour un phénomène similaire en mouvement de pointage). L'ajout de processus cognitifs conceptuels et orthographiques lors d'une tâche de dénomination d'images semble conduire à une stratégie de planification différente. ...
... Dans notre étude, l'utilisation d'une tablette LCD a donc pu modifier la préparation de la réponse verbale écrite par anticipation de la modification du feedback kinesthésique en plus du feedback visuel. Il semble que plus de temps soit alloué à la préparation motrice lorsqu'il est impossible aux participants de se baser sur les feedbacks sensoriels (kinesthésique et visuel) pour contrôler leur production (Khan et al., 2002). ...
... En revanche, sans contrainte temporelle, comme dans la présente expérience, les participants avaient la possibilité de prendre plus de temps pour mieux planifier leur production afin de garder une précision d'exécution correcte (Khan et al., 2002 ;van Doorn & Keuss, 1992). ...
... Overall the effects of vision are consistent with existing literature. Longer reaction times were expected during no-vision blocks as participants were likely using the time to solidify their representations of the target location, as they knew they would lose visual information upon movement initiation Khan, Elliott, Coull, Chua, & Lyons, 2002). Participants will plan movements based on the sensory feedback available during the movement, therefore in no-vision blocks, participants spend more time planning the movement so they can reach the target without visual feedback during the movement (Khan et al., 2002). ...
... Longer reaction times were expected during no-vision blocks as participants were likely using the time to solidify their representations of the target location, as they knew they would lose visual information upon movement initiation Khan, Elliott, Coull, Chua, & Lyons, 2002). Participants will plan movements based on the sensory feedback available during the movement, therefore in no-vision blocks, participants spend more time planning the movement so they can reach the target without visual feedback during the movement (Khan et al., 2002). In full vision blocks, participants took less time to plan the movement, as they can spend more time after peak deceleration using visual information to make online corrections (Elliott et al., 2010;Khan et al., 2002). ...
... Participants will plan movements based on the sensory feedback available during the movement, therefore in no-vision blocks, participants spend more time planning the movement so they can reach the target without visual feedback during the movement (Khan et al., 2002). In full vision blocks, participants took less time to plan the movement, as they can spend more time after peak deceleration using visual information to make online corrections (Elliott et al., 2010;Khan et al., 2002). This effect is evident in terms of movement time and peak velocity, with no-vision blocks eliciting shorter movement times and higher peak velocities than full vision. ...
Rhythmic auditory stimuli (RAS) have been proposed to improve motor performance in populations with and without sensorimotor impairments. However, the reasons for the reported benefits are poorly understood. One idea is that RAS may supplement intrinsic feedback when other sensory input is diminished. The current experiment tested this idea by removing vision during a goal-directed reaching task. We hypothesized that any improvements in movement performance due to the RAS would be greater when vision was removed. Twenty-two typically developing adults performed reaching movements to one of two targets with RAS presented before movement initiation, after movement initiation, both before and after movement initiation, and no sound, all with and without vision. Dependent variables were analyzed using a 2 vision by 2 sound-before by 2 sound-during repeated measures ANOVA. Conditions where the metronome was heard before movement initiation yielded shorter and less variable reaction times compared when there was no sound before the movement. The RAS heard before and during the movement independently impacted spatial aspects of the movement. Sound before movement initiation resulted in smaller endpoint error, primarily in the anterior-posterior axis. Sound during the movement resulted in smaller endpoint error, primarily in the mediolateral axis. In no-vision blocks, inclusion of RAS resulted in improved endpoint performance, indicating that RAS supplemented the motor system. The present results strengthen our understanding of sensory integration underlying reaching performance by demonstrating that sound heard before and during a reaching movement can improve motor performance by supplementing the motor system when vision is unavailable.
... That is, while there are two dichotomous components, the anticipation of online sensory feedback can greatly inform the planning process so much so that online control is contingent upon the pre-planned use of sensory information. To elucidate, prior knowledge of visual feedback for goal-directed movements typically elicits a larger magnitude force and shorter proportional time at peak velocity (i.e., positive skew in the time-course of movement velocity) (Hansen, Glazebrook, Anson, Weeks, & Elliott, 2006;Khan, Elliott, Coull, Chua, & Lyons, 2002;see Causer, Hayes, Hooper, & Bennett, 2017 for an example of oculomotor control in golf-putting). What's more, a suspected decline in the ability to control can cause an increasingly shorter proportion of time to peak velocity (Mottet, van Dokkum, Froger, Gouïach, & Laffont, 2017;Timmis & Pardhan, 2012;Welsh, Higgins, & Elliott, 2007). ...
... What's more, the uncertainty surrounding movement outcomes should drive a shorter primary movement and/or increase the frequency of undershoots for the high compared to low anxiety condition. Alternatively, the predominantly feedforward control perspective (go-for-it strategy) assumes that anxiety will invoke an inverse extension to the proportion of time to peak velocity (resembling a more symmetric velocity profile) Khan et al., 2002), increase the displacement at the primary movement (Khan, Franks, & Goodman, 1998), and decrease the frequency of two-component submovements (Elliott et al., 2014). Finally, the more extreme version of this approach may render a trade-off between speed and accuracy, where time-consuming visual feedbackbased corrections may be eradicated at the expense of a larger error rate for the high compared to low anxiety condition (see Carlton, 1981;Elliott & Madalena, 1987;Khan et al., 1998). ...
... Thus, the present study predicted that high anxiety will inflict increases in endpoint variability, which would be partially offset by a decrease during the earlier portions of the movement (peak acceleration/peak velocity/ peak deceleration). In keeping with the view of movement optimization or the play-it-safe strategy (Elliott et al., 2004;Elliott et al., 2010), the anticipation of upcoming sensory information assumes that an attenuation in control caused by high anxiety should subsequently extend the time spent after peak velocity (shorter proportion of time to peak velocity) Khan et al., 2002;Welsh et al., 2007). In addition, the growing uncertainty surrounding potential movement outcomes following high anxiety should generate a more profound tendency to undershoot the target in order to avoid time-and energyconsuming corrections (Elliott et al., 2004). ...
The anxiety-perceptual-motor performance relationship may be enriched by investigations involving discrete manual responses due to the definitive demarcation of planning and control processes, which comprise the early and late portions of movement, respectively. To further examine the explanatory power of self-focus and distraction theories, we explored the potential of anxiety causing changes to movement planning that accommodate for anticipated negative effects in online control. As a result, we posed two hypotheses where anxiety causes performers to initially undershoot the target and enable more time to use visual feedback (‘play-it-safe’), or fire a ballistic reach to cover a greater distance without later undertaking online control (‘go-for-it’). Participants were tasked with an upper-limb movement to a single target under counter-balanced instructions to execute fast and accurate responses (low/normal anxiety) with non-contingent negative performance feedback (high anxiety). The results indicated that the previously identified negative impact of anxiety in online control was replicated. While anxiety caused a longer displacement to reach peak velocity and greater tendency to overshoot the target, there appeared to be no shift in the attempts to utilise online visual feedback. Thus, the tendency to initially overshoot may manifest from an inefficient auxiliary procedure that manages to uphold overall movement time and response accuracy.
... The trajectory strategies towards static targets can be defined as modification of trajectory paths across trial repetitions. This can be evaluated by the analysis of motor variability at various stages throughout the movement (i.e., peak acceleration (PA), peak velocity (PV) and peak deceleration (PD); Khan et al., 2002Khan et al., , 2003. The rationale of this method was that if reaching movements are programmed and not altered, movement variability should increase as the movement progresses (Khan et al., 2002(Khan et al., , 2003. ...
... This can be evaluated by the analysis of motor variability at various stages throughout the movement (i.e., peak acceleration (PA), peak velocity (PV) and peak deceleration (PD); Khan et al., 2002Khan et al., , 2003. The rationale of this method was that if reaching movements are programmed and not altered, movement variability should increase as the movement progresses (Khan et al., 2002(Khan et al., , 2003. If corrections in the movement trajectory were made on the subsequent trial, the variability profiles would deviate from the programmed movement trajectory and differ between different stages of movement and across eye/target configurations. ...
... As measure of movement corrections along the motor execution, we performed an analysis of the variability of trajectories across trials. For each participant, (N = 12) we calculated standard deviations across trials in both Y (depth) and X (direction) dimensions at four relevant points of movement for trajectories described by the marker located on the index finger and that corresponded to: peak acceleration (point of maximum acceleration, PA), peak velocity (point of maximum velocity, PV), peak deceleration (point of maximum negative acceleration, PD) and the end of movement (END); then we averaged across the participants (Khan et al., 2002(Khan et al., , 2003Kasuga et al., 2015). We compared the distribution of spatial variability for eye-centered configurations (Constant gaze and Constant reach configurations) and for space-centered configurations (Constant gaze and Foveal reach configurations) in depth and direction by a two-way ANOVA (2 eye/target configurations × 4 points on the trajectory) and by a Bonferroni post hoc test when the interaction was significant. ...
Reaching behavior represents one of the basic aspects of human cognitive abilities important for the interaction with the environment. Reaching movements towards visual objects are controlled by mechanisms based on coordinate systems that transform the spatial information of target location into appropriate motor response. Although recent works have extensively studied the encoding of target position for reaching in three-dimensional space at behavioral level, the combined analysis of reach errors and movement variability has so far been investigated by few studies. Here we did so by testing 12 healthy participants in an experiment where reaching targets were presented at different depths and directions in foveal and peripheral viewing conditions. Each participant executed a memory-guided task in which he/she had to reach the memorized position of the target. A combination of vector and gradient analysis, novel for behavioral data, was applied to analyze patterns of reach errors for different combinations of eye/target positions. The results showed reach error patterns based on both eye- and space-centered coordinate systems: in depth more biased towards a space-centered representation and in direction mixed between space- and eye-centered representation. We calculated movement variability to describe different trajectory strategies adopted by participants while reaching to the different eye/target configurations tested. In direction, the distribution of variability between configurations that shared the same eye/target relative configuration was different, whereas in configurations that shared the same spatial position of targets, it was similar. In depth, the variability showed more similar distributions in both pairs of eye/target configurations tested. These results suggest that reaching movements executed in geometries that require hand and eye dissociations in direction and depth showed multiple coordinate systems and different trajectory strategies according to eye/target configurations and the two dimensions of space.
... However, it remains unknown whether the effects of occlusion can be negated if participants know in advance what visual information will be available, thus providing the opportunity to strategically adapt phases of both the quiet eye period and movement control. For example, it has been shown that in manual aiming movements, when an individual knows they will receive visual feedback they reduce movement planning (preprograming) time as they prepare to utilise vision for online control (Hansen et al. 2006;Khan et al. 2002). ...
... If preprograming alone occurs during the quiet eye period, we would expect no differences in outcome, or any changes in QE-online or QE-dwell between the two vision conditions. Conversely, if online visual control that would normally take place during the quiet eye period is eliminated by removing vision after movement onset, it can be expected that participants will adapt by increasing the duration of the QE-preprograming phase (Hansen et al. 2006;Khan et al. 2002). However, if online control is necessary during golf putting, it follows that a change in duration of QE-preprograming will not be sufficient to maintain performance accuracy in the occluded vision condition. ...
... Of the three phases of golf putting, we found that only the duration of the preparation phase was increased in the occluded vision condition compared to the full vision condition. This is consistent with participants spending more time planning and programming the putting action when vision was not available for online control (Hansen et al. 2006;Khan et al. 2002). It is noteworthy that the increase in duration of the preparation phase was not sufficient to overcome the loss of visual information and thus maintenance of outcome performance accuracy. ...
An occlusion protocol was used to elucidate the respective roles of preprograming and online control during the quiet eye period of golf putting. Twenty-one novice golfers completed golf putts to 6-ft and 11-ft targets under full vision or with vision occluded on initiation of the backswing. Radial error (RE) was higher, and quiet eye was longer, when putting to the 11-ft versus 6-ft target, and in the occluded versus full vision condition. Quiet eye durations, as well as preprograming, online and dwell durations, were longer in low-RE compared to high-RE trials. The preprograming component of quiet eye was significantly longer in the occluded vision condition, whereas the online and dwell components were significantly longer in the full vision condition. These findings demonstrate an increase in preprograming when vision is occluded. However, this was not sufficient to overcome the need for online visual control during the quiet eye period. These findings suggest the quiet eye period is composed of preprograming and online control elements; however, online visual control of action is critical to performance.
... Furthermore, the two components are recognized as two distinct strategies of motor control: impulse control and limb-target control . Impulse control refers to rapid adjustments for the motor planning in the early phase, while limbtarget control involves discrete corrections that reduce discrepancies between the limb and target position in the late phase (Elliott et al., 2017;Khan et al., 2002;Khan & Franks, 2003). According to the control strategies, spatiotemporal metrics of specific movements were analyzed to characterize the performance of sensoryguided motor behavior in immersive virtual environments (Rao et al., 2018). ...
... Motor control, including impulse control and limb-target control, is believed to play an important role in goaldirected movements (Elliott et al., 2017). The spatial variability of the movement is highly associated with both neural-motor noise and planning errors, which can be corrected by impulse control (Elliott et al., 2009;Khan et al., 2002). Previous studies revealed significant differences in spatial variability between movements performed with heavy and light objects (Burkitt et al., 2015). ...
The inertia of manipulated objects contributes to natural human performance, but its effects on virtual reality (VR) interactions have rarely been investigated. Here, we designed a virtual goal-directed task, in which virtual objects with different masses were moved into a target hole. Based on synchronized kinematic and eye-tracking data, we examined the effects of inertia on participants’ performance during the virtual task in a virtual environment. Our results indicated that hand movements presented greater spatial variability and more discontinuities when the inertial load was removed. It suggested a decline in the ability of motor control and feedback regulation, since the absence of an inertial load weakened the proprioception for sensing limb movements. Eye-movement evidence indicated that increased preferential allocations of visual attention contribute to compensating the weakened proprioceptive cues, supporting the kinematic results. These findings reveal the importance and mechanism of inertial effects on human behaviors in VR interactions.
... Such disruption of performance due to randomization is widespread in motor tasks (Elliott and Allard, 1985;Edin et al., 1992;Horak and Diener, 1994;Khan et al., 2002;Pruszynski et al., 2008;Selen et al., 2009;Bennett et al., 2010;Afsanepurak et al., 2012) (but see White and Diedrichsen, 2013). For instance, in a recent study (Orban de Xivry, 2013), we asked participants to reach to either a narrow or wide target and found that participants reacted differently to a perturbation in function of the target width (compatible with the minimum intervention principle of optimal control, Todorov and Jordan, 2002) but unexpectedly also in function of the schedule (random or blocked). ...
... ; https://doi.org/10.1101/047621 doi: bioRxiv preprint extends far beyond our simple task (Elliott and Allard, 1985;Edin et al., 1992;Horak and Diener, 1994;Khan et al., 2002;Pruszynski et al., 2008;Afsanepurak et al., 2012). Here, we provide for the first time, an account for this phenomenon. ...
Movement planning consists of choosing the endpoint of the movement and selecting the motor program that will bring the effector on the endpoint. It is widely accepted that movement endpoint is updated on a trial-by-trial basis with respect to the observed errors and that the motor program for a given movement follows the rules of optimal feedback control. Here, we show clear limitations of these predictions because of the existence of a switching cost for motor planning. First, this cost prevented participants from tuning their motor program appropriately for each individual trial. This was true even when the participants selected the width of the target that they reached toward or when they had learned the appropriate motor program previously. These data are compatible with the existence of a switching cost such as those found in cognitive studies. Interestingly, this cost of switching shares many features of costs reported in cognitive task switching experiments and, when tested in the same participants, was correlated with it. Second, we found that randomly changing the width of a target over the course of a reaching experiment prevents the motor system from updating the endpoint of movements on the basis of the performance on the previous trial if the width of the target has changed. These results provide new insights into the process of motor planning and how it relates to optimal control theory and to a selection by consequences process rather than to an error-based process for action selection.
... Dependent variables included movement time (time from movement start to movement end), time to peak velocity (time from movement start to peak velocity), time after peak velocity (time from peak velocity to movement end), distance traveled by the primary movement in the primary direction of movement, constant error (distance from end position of the effector to the target in the primary direction of movement), variable error (standard deviation of constant error), and reaction time (the time from the presentation of auditory stimulus to movement start). Trajectory variability was also examined using the standard deviations of the condition average positions for participants at the kinematic landmarks of peak acceleration, peak velocity, peak deceleration, and movement end (Khan et al. 2002). Trials were removed before analysis if IRED visibility was disturbed during a movement or if participants moved before the auditory cue (i.e., anticipated the upcoming movement). ...
... This greater propensity to undershoot the target with the primary movement in the non-dominant limb is likely a strategy that constrains the higher late trajectory (i.e., at peak deceleration) spatial variability and limits the amount of time and energy-costly target overshoot misses (Welsh et al. 2007;Elliott et al. 2004;Lyons et al. 2006;Burkitt et al. 2015). The greater spatial variability at peak deceleration coupled with a rapid decrease in spatial variability at movement end in the non-dominant limb suggests a propensity to use feedback information towards the end of the movement and engage in late limb-target control (Khan et al. 2002;Burkitt et al. 2015). In contrast, force specification and feedforward processing are likely better in the dominant limb, making it less variable at peak deceleration. ...
Subclinical neck pain (SCNP) refers to recurrent neck pain and/or stiffness for which individuals have not yet sought treatment. Prior studies have shown that individuals with SCNP have altered cerebellar processing that exhibits an altered body schema. The cerebellum also plays a vital role in upper limb reaching movements through refining internal models and integrating sensorimotor information. However, the impact of SCNP on these processes has yet to be examined in the context of a rapid goal-directed aiming response that relies on feedforward and feedback processes to guide the limb to the target. To address this, SCNP and control participants performed goal-directed upper limb movements with the dominant and non-dominant hands using light and heavy styli in the horizontal plane. The results show greater peak accelerations in SCNP participants using the heavy stylus. However, there were no other group differences seen, possibly due to the fact that reaching behavior predominantly relies on vision such that any proprioceptive deficits seen in those with SCNP can be compensated. This study illustrates the robust compensatory nature of the CNS when performing end-effector reaching tasks, suggesting studies altering visual feedback may be needed to see the full impact of SCNP on upper limb aiming.
... Studies on visuomotor and multisensory-motor integration have shown that providing vision during movement execution is a conditio sine qua non to guarantee the best movement performance. Specifically, reaching movements when vision is available during both movement planning and movement execution are more precise than when vision is withheld just after movement onset (Keele & Posner, 1968;Elliott & Madalena, 1987;Blouin, Bard, Teasdale, & Fleury, 1993;Rossetti, Stelmach, Desmurget, Prablanc, & Jeannerod, 1994;Westwood, Heath, & Roy, 2001;Khan, Elliott, Coull, Chua, & Lyons, 2002;Khan et al., 2006;Kennedy, Bhattacharjee, Hansen, Reid, & Tremblay, 2015;Tremblay et al., 2017). Similarly, the precision of reaching movements toward visuo-haptic targets is also reduced if vision is provided only during the planning phase, even though haptic information is provided for the whole movement duration (Desmurget et al., 1997;Monaco et al., 2010;. ...
... This study shows that reaching movements towards visuo-haptic targets are guided by a multisensory integration process even when the visual exposure to the haptic target during the planning phase is as short as 50 ms. Supplementing haptic information with very brief vision is thus sufficient to trigger a multisensory advantage that persists until the end of the action, even though vision provided only during the planning phase does not lead to the same level of precision as when it is provided during the whole movement (Keele & Posner, 1968;Elliott & Madalena, 1987;Blouin et al., 1993;Rossetti et al., 1994;Khan et al., 2002;Khan et al., 2006;Kennedy et al., 2015;Tremblay et al., 2017;Fig. 6. Top row: Credible difference distributions of the endpoint variability in the azimuth and depth direction for the comparisons between the H Full condition and the conditions of the HV t block. ...
Goal-directed aiming movements toward visuo-haptic targets (i.e., seen and handheld targets) are generally more precise than those toward visual only or haptic only targets. This multisensory advantage stems from a continuous inflow of haptic and visual target information during the movement planning and execution phases. However, in everyday life, multisensory movements often occur without the support of continuous visual information. Here we investigated whether and to what extent limiting visual information to the initial stage of the action still leads to a multisensory advantage. Participants were asked to reach a handheld target while vision was briefly provided during the movement planning phase (50 ms, 100 ms, 200 ms of vision before movement onset), or during the planning and early execution phases (400 ms of vision), or during the entire movement. Additional conditions were performed in which only haptic target information was provided, or, only vision was provided either briefly (50 ms, 100 ms, 200 ms, 400 ms) or throughout the entire movement. Results showed that 50 ms of vision before movement onset were sufficient to trigger a direction-specific visuo-haptic integration process that increased endpoint precision. We conclude that, when a continuous support of vision is not available, endpoint precision is determined by the less recent, but most reliable multisensory information rather than by the latest unisensory (haptic) inputs.
... Therefore, in the case of reaching movements, optimal motor performance depends on the interaction between feedforward control (i.e., generate a large force to accelerate the limb ballistically towards the target) and feedback control (i.e., use sensory feedback to correct trajectory errors as the arm approaches the target) [23,156]. Recording limb kinematics using a high-speed motion camera provides insight into feedforward and feedback control processes [117,157]. For example, peak acceleration occurs within the first 100 ms after movement onset. ...
... In contrast, the control group displayed a different control strategy in which a longer deceleration interval duration was associated with a higher endpoint precision. Results from the control group are consistent with a large body of research, which shows that opti-mal movement execution depends on the interaction between feedforward and feedback control where trajectory errors, due to a large initial acceleration force, are seamlessly corrected online to achieve fast, accurate, and precise movements [155,157,160,161]. Importantly, artificially reducing visual acuity in one eye using plus lenses to simulate mild amblyopia in adults with normal vision did not affect their reach kinematics significantly [162]. ...
Amblyopia is a neurodevelopmental visual disorder arising from decorrelated binocular experience during the critical periods of development. The hallmark of amblyopia is reduced visual acuity and impairment in binocular vision. The consequences of amblyopia on various sensory and perceptual functions have been studied extensively over the past 50 years. Historically, relatively fewer studies examined the impact of amblyopia on visuomotor behaviours; however, research in this area has flourished over the past 10 years. Therefore, the aim of this review paper is to provide a comprehensive review of current knowledge about the effects of amblyopia on eye movements, upper limb reaching and grasping movements, as well as balance and gait. Accumulating evidence indicates that amblyopia is associated with considerable deficits in visuomotor behaviour during amblyopic eye viewing, as well as adaptations in behaviour during binocular and fellow eye viewing in adults and children. Importantly, due to amblyopia heterogeneity, visuomotor development in children and motor skill performance in adults may be significantly influenced by the etiology and clinical features, such as visual acuity and stereoacuity. Studies with larger cohorts of children and adults are needed to disentangle the unique contribution of these clinical characteristics to the development and performance of visuomotor behaviours.
... Although proprioceptive manipulations yielded differences in the average movement endpoint biases (i.e., constant error), it was not possible to detect differences in the trajectories. Presumably, this was because experimental conditions (i.e., presentation of proprioceptive and visual perturbations) were presented in a blocked fashion, which likely caused the participants to adopt different planning mechanisms (e.g., Khan et al. 2002;Elliott et al. 2004;Hansen et al. 2006). The current study attempted to better determine the utilization of vision and proprioception by presenting visual feedback in a pseudo-random fashion. ...
... Thus, planning mechanisms may have been different during the blocked vibration vs. no vibration trials. Additionally, advance knowledge of visual feedback can alter planning and online control mechanisms (Elliott et al. 2004;Hansen et al. 2006;Khan et al. 2002), which can explain the expected differences in the results from Goodman et al. (2018). In that recent study, we employed blocked vision and tendon vibration trials (see above) while in the current study, tendon vibration trials were blocked and vision conditions were pseudo-randomized. ...
Visual feedback is crucial for movement accuracy (e.g., Keele and Posner, J Exp Psychol 77:155-158, 1968). As well, proprioception has been argued to be important for the control of voluntary movements (e.g., Bagesteiro et al., Exp Brain Res 171:358-370, 2006; Rossetti et al., J Neurophysiol 74:457-463, 1995). While tendon vibration (TVib) has been used to perturb proprioceptive information during limb matching tasks (Goodwin et al., Science 175:1382-1384, 1972), the current study employed between-trial dual-muscle TVib, coupled with vision occlusion, to assess the use of vision and proprioception for the online control of voluntary movements. Participants (n = 17) performed an upper-limb reaching task (30 cm). TVib influenced both accuracy and precision of movement endpoint. Critically, variability analyses showed that participant's performance was most affected by TVib at 75% of the movement duration, even in the presence of vision. These findings demonstrate that between-trial dual-muscle tendon vibration can perturb proprioceptive feedback, and further, suggest that proprioception can be important for the online control of reaches, even when vision is available.
... For long movements, and as per Fitts' law, there is a balance between pre-programmed ballistic movements and feedback-mediated refinements (Fitts, 1954;Klapp, 1975;Kopper et al., 2010). Through repeated trials of reaching to static targets, when visual feedback is available, kinematics typically change so that movements are made at reduced speeds with more time spent refining movement trajectories with the available visual information (Khan et al., 2002;Heath, 2005). ...
... The observation that these changes are most strongly reflected in the balance of ballistic versus refinement movements, points to this inflection as a key stage wherein visual feedback can alter performance and guide learning (Khan and Franks, 2003). With visual information continuously available through the trial, one would expect that larger portion of the movement would be spent in the feedback-based refinement phase (Khan et al., 2002;Heath, 2005). In this 3D simulation, however, the targets become smaller the further they travel, making intercepting them harder at longer delays. ...
Sensorimotor learning refers to improvements that occur through practice in the performance of sensory-guided motor behaviors. Leveraging novel technical capabilities of an immersive virtual environment, we probed the component kinematic processes that mediate sensorimotor learning. Twenty naïve subjects performed a simulated marksmanship task modeled after Olympic Trap Shooting standards. We measured movement kinematics and shooting performance as participants practiced 350 trials while receiving trial-by-trial feedback about shooting success. Spatiotemporal analysis of motion tracking elucidated the ballistic and refinement phases of hand movements. We found systematic changes in movement kinematics that accompanied improvements in shot accuracy during training, though reaction and response times did not change over blocks. In particular, we observed longer, slower, and more precise ballistic movements that replaced effort spent on corrections and refinement. Collectively, these results leverage developments in immersive virtual reality technology to quantify and compare the kinematics of movement during early learning of full-body sensorimotor orienting.
... Object-centered information may play a larger role when it is consistently available, compared with when it is not consistently available. In support, the use of visual feedback in reaching and grasping depends on implicit knowledge about its availability, resulting in larger differences in kinematic parameters when visual feedback is present in all trials than when trials with and without visual feedback follow in random or alternating order (Elliott & Allard, 1985;Jakobson & Goodale, 1991;Khan, Elliott, Coull, Chua, & Lyons, 2002;Whitwell, Lambert, & Goodale, 2008;Zelaznik, Hawkins, & Kisselburgh, 1983). A second aim of our study was to test whether the contribution of objectcentered information is dependent on its availability. ...
... Rather, the use of information is dependent on implicit knowledge about the availability of this information. This in is accordance with the finding that the use of visual feedback in reaching and grasping is dependent on the presentation schedule (Elliott & Allard, 1985;Jakobson & Goodale, 1991;Khan et al., 2002;Whitwell et al., 2008;Zelaznik et al., 1983). ...
The position of a saccade target can be encoded in gazecentered coordinates, that is, relative to the current gaze position, or in object-centered coordinates, that is, relative to an object in the environment. We tested the role of gaze-centered and object-centered coding in a double-step saccade task involving the Brentano version of the Müller-Lyer illusion. The two visual targets were presented either sequentially, requiring gaze-centered coding of the second saccade target, or simultaneously, thereby providing additional object-centered information about the location of the second target relative to the first. We found that the endpoint of the second saccade was affected by the illusion, irrespective of whether the targets were presented sequentially or simultaneously, suggesting that participants used a gazecentered updating strategy. We found that variability in saccade endpoints was reduced when object-centered information was consistently available but not when its presence varied from trial to trial. Our results suggest that gaze-centered coding is dominant in the planning of sequential saccades, whereas object-centered information plays a relatively small role.
... It is, however, important to recognize that McIntosh and Buonocore used a blocked target location paradigm such that within a block of 70 trials the target appeared either left or right of a central fixation. As such, participants were provided advanced information related to the location of both the target and the distractor-a manipulation that may have reduced online response planning and negated distractor-related planning effects (Khan et al. 2002;see also DeSimone et al. 2015). As such, we investigated distractor-related effects on goal-directed reaches wherein target and distractor (i.e., proximal and remote) locations could not be predicted in advance of their onset; that is, target and distractor locations were varied on a trialby-trial basis. ...
... Notably, if the visual property of the distractor influences antipointing (and propointing) then RTs should be increased due to a longrange intercollicular inhibitory pathway (i.e., the horizontal capped line). In turn, the row-labeled "Motor-related activity" (D) shows that antipointing motor activity of target and distractor are proximal (i.e., in the same visual field) a response then the direct stimulus-response mapping for propointing trials would have permitted feedback related to endpoint accuracy and therefore supported online control and offline learning (see Heath et al. 2009a, b;Maraj and Heath 2010; see also Khan et al. 2002). Of course, no such feedback would have been possible for antipointing trials because the required response was mirror-symmetrical to the target location. ...
The saccade literature has consistently reported that the presentation of a distractor remote to a target increases reaction time (i.e., the remote distractor effect: RDE). As well, some studies have shown that a proximal distractor facilitates saccade reaction time. The lateral inhibition hypothesis attributes the aforementioned findings to the inhibition/facilitation of target selection mechanisms operating in the intermediate layers of the superior colliculus (SC). Although the impact of remote and proximal distractors has been extensively examined in the saccade literature, a paucity of work has examined whether such findings generalize to reaching responses, and to our knowledge, no work has directly contrasted reaching RTs for remote and proximal distractors. To that end, the present investigation had participants complete reaches
in target only trials (i.e., TO) and when distractors were presented at “remote” (i.e., the opposite visual field) and
“proximal” (i.e., the same visual field) locations along the same horizontal meridian as the target. As well, participants reached to the target’s veridical (i.e., propointing) and mirror-symmetrical (i.e., antipointing) location. The basis for contrasting pro- and antipointing was to determine whether the distractor’s visual- or motor-related activity influence reaching RTs. Results demonstrated that remote and proximal distractors, respectively, increased and decreased reaching RTs and the effect was consistent for pro- and antipointing. Accordingly, results evince that the RDE and the facilitatory effects of a proximal distractor are effector
independent and provide behavioral support for the contention that the SC serves as a general target selection mechanism. As well, the comparable distractor-related effects for pro- and antipointing trials indicate that the visual properties of remote and proximal distractors respectively inhibit and facilitate target selection.
... In the second experiment, we examine the effects of the sequence of trials with different judgments (cursor or hand) on explicit and implicit measures of hand direction. Trial history is known to affect various behaviors, such as grip force production (Johansson and Westling, 1988;Lukos et al., 2013), reaction time (Kirby, 1980;Song and Nakayama, 2007), aiming movements (Zelaznik et al., 1983;Khan et al., 2002;Song and Nakayama, 2007;Cheng et al., 2008), reach-to-grasp movements (Rand et al., 2004;Whitwell et al., 2008;Whitwell and Goodale, 2009), and saccadic eye movements toward visual targets (Fecteau and Munoz, 2003). Implicitly and explicitly measured biases of hand direction are no exception: found that they were affected by the immediate trial history, that is, by the local context, in opposite directions. ...
... We studied the effects of global context by means of a methodology used by Zelaznik et al. (1983) and others (Khan et al., 2002;Song and Nakayama, 2007;Whitwell et al., 2008). The principle is to compare two types of trials under three different conditions with blocked, alternated, and randomized order. ...
In a cursor-control task in which the motion of the cursor is rotated randomly relative to the movement of the hand, the sensed directions of hand and cursor are mutually biased. In our previous study, we used implicit and explicit measures of the bias of sensed hand direction toward the direction of the cursor and found different characteristics. The present study serves to explore further differences and commonalities of these measures. In Experiment 1, we examined the effects of different relative reliabilities of visual and proprioceptive information on the explicitly and implicitly assessed bias of sensed hand direction. In two conditions, participants made an aiming movement and returned to the start position immediately or after a delay of 6 s during which the cursor was no longer visible. The unimodal proprioceptive information on final hand position in the delayed condition served to increase its relative reliability. As a result, the bias of sensed hand direction toward the direction of the cursor was reduced for the explicit measure, with a complementary increase of the bias of sensed cursor direction, but unchanged for the implicit measure. In Experiment 2, we examined the influence of global context, specifically of the across-trial sequence of judgments of hand and cursor direction. Both explicitly and implicitly assessed biases of sensed hand direction did not significantly differ between the alternated condition (trial-to-trial alternations of judgments of hand and cursor direction) and the blocked condition (judgments of hand or cursor directions in all trials). They both substantially decreased from the alternated to the randomized condition (random sequence of judgments of hand and cursor direction), without a complementary increase of the bias of sensed cursor direction. We conclude that our explicit and implicit measures are equally sensitive to variations of coupling strength as induced by the variation of global context in Experiment 2, but are differently sensitive to variations of the relative reliabilities as induced by our additional unimodal proprioceptive information in Experiment 1.
... Secondly, individuals' propensity to adopt this strategy may be an attempt to gain more explicit control over movements and are positively predicted by conscious processing propensity. A similar strategy has been observed by Khan, Elliott, Coull, Chua, and Lyons (2002) when individuals were uncertain about upcoming visual conditions. Thirdly, when the need for correction is great enough (e.g., via artificial cursor jumps), participants' strategy to attenuate online corrections may be automatically overturned online. ...
Via three experiments, we investigated heightened anxiety's effect on the offline planning and online correction of upper-limb target-directed aiming movements. In Experiment 1, the majority of task trials allowed for the voluntary distribution of offline planning and online correction to achieve task success, while a subset of cursor jump trials necessitated the use of online correction to achieve task success. Experiments 2 and 3 replicated and elaborated Experiment 1 by assessing movement-specific reinvestment propensity and manipulating the self-control resources of participants. This allowed more detailed inference of cognitive resource utilisation to tease apart the effects of conscious processing and distraction-based anxiety mechanisms. For the first time, we demonstrate that: anxiety-induced online-to-offline motor control shifts can be overridden when the need for online correction is necessitated (i.e., in jump trials); anxiety-induced online-to-offline shifts seem to be positively predicted by conscious processing propensity; and optimal spatial efficacy of limb information-based online correction seems to require cognitive resources. We conclude that long-standing definitions of limb information-based online correction require revision, and that both conscious processing and distraction theories appear to play a role in determining the control strategies of anxiety induced upper limb target directed aiming movements.
... These experiments have revealed that movement errors can be corrected in subsequent trials by engaging in offline planning, where offline planning processes occur before movement initiation and are presumed to be responsible for getting the hand in the vicinity of the target [4,[8][9][10]. As well, movement errors can be corrected during movement execution in order to reduce the error between one's hand and target, thus demonstrating online control processes [11][12][13][14][15]. The contribution of offline planning and online control processes, and hence how movements are corrected, is determined by evaluating movement outcome, as well as kinematic variables related to reach performance. ...
The ability to accurately complete goal-directed actions, such as reaching for a glass of water, requires coordination between sensory, cognitive and motor systems. When these systems are impaired, like in people with multiple sclerosis (PwMS), deficits in movement arise. To date, the characterization of upper limb performance in PwMS has typically been limited to results attained from self-reported questionnaires or clinical tools. Our aim was to characterize visually guided reaching performance in PwMS. Thirty-six participants (12 PwMS who reported upper limb impairment (MS-R), 12 PwMS who reported not experiencing upper limb impairment (MS-NR), and 12 age- and sex-matched control participants without MS (CTL)) reached to 8 targets in a virtual environment while seeing a visual representation of their hand in the form of a cursor on the screen. Reaches were completed with both the dominant and non-dominant hands. All participants were able to complete the visually guided reaching task, such that their hand landed on the target. However, PwMS showed noticeably more atypical reaching profiles when compared to control participants. In accordance with these observations, analyses of reaching performance revealed that the MS-R group was more variable with respect to the time it took to initiate and complete their movements compared to the CTL group. While performance of the MS-NR group did not differ significantly from either the CTL or MS-R groups, individuals in the MS-NR group were less consistent in their performance compared to the CTL group. Together these findings suggest that PwMS with and without self-reported upper limb impairment have deficits in the planning and/or control of their movements. We further argue that deficits observed during movement in PwMS who report upper limb impairment may arise due to participants compensating for impaired movement planning processes.
... The simulations confirmed the proper role of (Figure 16, black; see Figure 11A) and showed that variability produced by the other sources of noise did not comply to Fitts' law, i.e. there was no univocal relationship between movement duration and ( Figure 16, red, green, blue, purple, yellow). (Heath, Neely, & Krigolson, 2008; Figure 18B); 3. correlation between the value of kinematic landmarks (Messier & Kalaska, 1999; Figure 18C); 4. positional standard deviation at normalized time (Liu & Todorov, 2007; Figure 18D); 5. positional standard deviation of kinematic landmarks (Khan, Elliot, Coull, Chua, & Lyons, 2002; Figure 18E); 6. temporal standard deviation of kinematic landmarks (Valdez & Amazeen, 2008; Figure 18F). Each panel in Figure 18 shows simulations with 6 types of noise (colored lines, circles) and ...
Motor control is a fundamental process that underlies all voluntary behavioral responses. Several different theories based on different principles (task dynamics, equilibrium-point theory, passive-motion paradigm, active inference, optimal control) account for specific aspects of how actions are produced, but fail to provide a unified view on this problem. Here, we propose a concise theory of motor control based on three principles: optimal feedback control, control with a receding time horizon, and task representation by a series of via-points updated at fixed frequency. By construction, the theory provides a suitable solution to the degrees-of-freedom problem, that is, trajectory formation in the presence of redundancies and noise. We show through computer simulations that the theory also explains the production of discrete, continuous, rhythmic, and temporally constrained movements, and their parametric and statistical properties (scaling laws, power laws, speed/accuracy trade-offs). The theory has no free parameters and only limited variations in its implementation details and in the nature of noise are necessary to guarantee its explanatory power. (PsycInfo Database Record (c) 2021 APA, all rights reserved).
... The simulations confirmed the proper role of (Figure 16, black; see Figure 11A) and showed that variability produced by the other sources of noise did not comply to Fitts' law, i.e. there was no univocal relationship between movement duration and ( Figure 16, red, green, blue, purple, yellow). We assessed basic aspects of correlation, spatial and temporal variability across repetitions of a movement of a given amplitude ( Figure 18): 1. correlation between position at kinematic landmarks and endpoint position (Heath, Westwood, & Binsted, 2004; Figure 18A); 2. correlation between position at normalized time and endpoint position (Heath, Neely, & Krigolson, 2008; Figure 18B); 3. correlation between the value of kinematic landmarks (Messier & Kalaska, 1999; Figure 18C); 4. positional standard deviation at normalized time (Liu & Todorov, 2007; Figure 18D); 5. positional standard deviation of kinematic landmarks (Khan, Elliot, Coull, Chua, & Lyons, 2002; Figure 18E); 6. temporal standard deviation of kinematic landmarks (Valdez & Amazeen, 2008; Figure 18F). Each panel in Figure 18 shows simulations with 6 types of noise (colored lines, circles) and experimental data (gray lines, triangles) which are characteristic of properties reported in the literature. ...
Motor control is a fundamental process that underlies all voluntary behavioral responses. Several different theories based on different principles (task dynamics, equilibrium-point theory, passive-motion paradigm, active inference, optimal control) account for specific aspects of how actions are produced, but fail to provide a unified view on this problem. Here we propose a concise theory of motor control based on three principles: optimal feedback control, control with a receding time horizon, and task representation by a series of via-points updated at fixed frequency. By construction, the theory provides a suitable solution to the degrees-of-freedom problem, i.e. trajectory formation in the presence of redundancies and noise. We show through computer simulations that the theory also explains the production of discrete, continuous, rhythmic and temporally-constrained movements, and their parametric and statistical properties (scaling laws, power laws, speed/accuracy tradeoffs). The theory has no free parameters and only limited variations in its implementation details and in the nature of noise are necessary to guarantee its explanatory power.
... The effects related to vision were consistent with existing literature and can be attributed to differences in movement planning based on the availability of sensory information (Elliott et al., 2010;Hansen et al., 2006;Khan et al., 2002), and online error correction based on visual feedback (Carson et al., 1990;Chua & Elliott, 1993;Elliott et al., 2010). There were no significant interactions between auditory condition and vision. ...
Music and metronomes differentially impact movement performance. The current experiment presented metronome and drum beats in simple and complex rhythms before goal-directed reaching movements, while also quantifying enjoyment. Auditory conditions were completed with and without visual feedback and were blocked and counterbalanced. There were no differences between simple and complex rhythms, indicating that rhythmic information alone is sufficient to benefit performance. The drum elicited shorter movement times and higher peak velocities, without an increase in spatial variability. Reaction times were moderately correlated with ratings of enjoyment. These data provide evidence that the source of an auditory stimulus impacts movement performance of a goal-directed reaching task. Results are contextualized within models of goal-directed reaching to elucidate mechanisms contributing to performance improvements.
... This interpretation coincides with reduced spatial variability (for similar findings within a reaching and grasping task, see Sacheli et al. 2013) despite there being a higher magnitude of peak velocity (see Meyer et al. 1988;Schmidt et al. 1979). Thus, it is possible that performers altered their pre-response planning by keeping the spatial variability of the initial movement comparatively low to minimise the need for online control later within the movement (Allsop et al. 2017;Roberts et al. 2018), while limiting the negative effects on endpoint accuracy and precision (Khan et al. 2002;see also, Fischman and Reeve 1992). Indeed, pre-response planning usually entails the optimal selection or parameterization of movement that most likely limits the inherent sources of variability (Hamilton and Wolpert 2002;Hamilton et al. 2004;Harris and Wolpert 1998; see also, van Beers 2009). ...
The task constraints imposed upon a co-actor can often influence our own actions. Likewise, the observation of somebody else’s movements can involuntarily contaminate the execution of our own movements. These joint action outcomes have rarely been considered in unison. The aim of the present study was to simultaneously examine the underlying processes contributing to joint action. We had pairs of participants work together to execute sequential aiming movements between two targets – the first person’s movement was contingent upon the anticipation of the second person’s movement (leader), while the second person’s movement was contingent upon the direct observation of the first person’s movement (follower). Participants executed separate blocks of two-target aiming movements under different contexts; that is, solely on their own using one (2T1L) and two (2T2L) of their upper limbs, or with another person (2T2P). The first movement segment generally indicated a more abrupt approach (shorter time after peak velocity, greater displacement and magnitude of peak velocity), which surprisingly coincided with lower spatial variability, for the 2T2P context. Meanwhile, the second segment indicated a similar kinematic profile as the first segment for the 2T2P context. The first movement of the leader appeared to accommodate the follower for their movement, while the second movement of the follower was primed by the observation of the leader’s movement. These findings collectively advocate two distinct levels of joint action including the anticipation (top-down) and mapping (bottom-up) of other people’s actions.
... When we considered the spatial variability of the cursor (i.e., the object that was controlled in both unimanual and bimanual tasks) in the direction perpendicular to the reach, we found that consistent with prior studies (Khan et al., 2002), the variability showed a distinct pattern during the reach; this was characterized by low variability at the start and end of the movement, and peak variability occurring at about 50% into the movement. This variability profile of the cursor was also reflected in the variability of the arm in unimanual tasks because there was no redundancy in the unimanual task. ...
Stroke often results in hemiparesis, leaving one side of the body ‘affected’ relative to the other side. Prior research has shown that the affected arm has higher variability – however, the extent to which this variability can be modulated is unclear. Here we used a shared bimanual task to examine the degree to which participants could modulate the variability in the affected arm after stroke. Participants with chronic stroke (n = 11), and age-matched controls (n = 11) performed unimanual and bimanual reaching movements to move a cursor on a screen to different targets. In the unimanual condition, the cursor was controlled only by the movement of a single arm whereas in the bimanual condition, the cursor position was “shared” between the two arms by using a weighted average of the two hand positions. Unknown to the participants, we altered the weightings of the affected and unaffected arms to cursor motion and examined how the movement variability on each arm changed depending on its contribution to the task. Results showed that stroke survivors had higher movement variability on the affected arm – however, like age-matched controls, they were able to modulate the variability in both the affected and unaffected arms according to the weighting condition. Specifically, as the weighting on a particular arm increased (i.e. it became more important to the task), the movement variability decreased. These results show that stroke survivors are capable of modulating variability depending on the task context, and this feature may potentially be exploited for rehabilitation paradigms
... When there is uncertainty about the availability of feedback the performer prepares their movement for the worst-case (or no vision) scenario. Specifically, they take more time to prepare their movements, produce more symmetric movement trajectories and undershoot the target position to a greater extent with their primary movement (Burkitt et al. 2013;Hansen et al. 2006;Khan et al. 2002;see Elliott et al. 2017 for a full review). ...
Several years ago, our research group forwarded a model of goal-directed reaching and aiming that describes the processes involved in the optimization of speed, accuracy, and energy expenditure (Elliott et al. 2010). One of the main features of the model is the distinction between early impulse control, which is based on a comparison of expected to perceived sensory consequences, and late limb-target control that involves a spatial comparison of limb and target position. Our model also emphasizes the importance of strategic behaviors that limit the opportunity for worst-case or inefficient outcomes. In the 2010 paper, we included a section on how our model can be used to understand atypical aiming/reaching movements in a number of special populations. In light of a recent empirical and theoretical update of our model (Elliott et al. 2017), here we consider contemporary motor control work involving typical aging, Down syndrome, autism spectrum disorder, and tetraplegia with tendon transfer surgery. We outline how atypical limb control can be viewed within the context of the multiple process model of goal-directed reaching and aiming, and discuss the underlying perceptual-motor impairment that results in the adaptive solution developed by the specific group.
... Several past studies, such as 21,22,[31][32][33] , similarly observed that spatial dispersion increases in the initial phase and that it reduces in the final phase of the goal-directed reaching movements. However, they did not study the temporary target of the initial sub-movement, nor did they make any hypothesis or implications about it. ...
Goal-directed human reaching often involves multi-component strategy with sub-movements. In general, the initial sub-movement is fast and less precise to bring the limb’s endpoint in the vicinity of the target as soon as possible. The final sub-movement then corrects the error accumulated during the previous sub-movement in order to reach the target. We investigate properties of a temporary target of the initial sub-movement. We hypothesise that the peak spatial dispersion of movement trajectories in the axis perpendicular to the movement is in front of the final reaching target, and that it indicates the temporary target of the initial sub-movement. The reasoning is that the dispersion accumulates, due to signal-dependent noise during the initial sub-movement, until the final corrective sub-movement is initiated, which then reduces the dispersion to successfully reach the actual target. We also hypothesise that the reaching movement distance and size of the actual target affect the properties of the temporary target of the initial sub-movement. The increased reaching movement distance increases the magnitude of peak dispersion and moves its location away from the actual target. On the other hand, the increased target size increases the magnitude of peak dispersion and moves its location closer to the actual target.
... In an aiming movement, these control mechanisms involve any movement adjustments necessary to correct discrepancies between the end of a limb's initial impulse and its target (Elliott, Helsen, & Chua, 2001;Woodworth, 1899). With both planning and control mechanisms heavily integrated, it would be remiss not to consider them in the context of one another, especially being that aiming movements incorporate both pre-planned offline (feedforward) and online (somatosensory) adjustments (Elliott, Chua, Pollock, & Lyons, 1995, p. 20 &;Wolpert and Kawato, 1998;Khan, Elliott, Coull, Chua, & Lyons, 2002;Elliott et al., 2014). ...
Abstract
Whilst benefits of an external focus are shown to govern several characteristics of skill execution, specificity theory indicates that sources of afferent information most useful to performance execution are typically prioritised during processing.
Objectives
We investigated whether an internal focus facilitates performance when pertinent afferent information is proprioceptive in nature and congruent with attentional focus. We also considered whether the mechanisms behind attentional focus differences are attributable to planning processes or online motor control.
Design
Experiments 1 and 2 adopted a randomised design, whilst experiment 3 used a repeated measures approach.
Method
In Experiment 1 we investigated movement variability as a measure of planning and error correction under external and internal focus conditions in an aiming task. Experiment 2 removed visual information to increase pertinence of proprioceptive feedback for movement execution and Experiment 3 adopted a leg-extension task, where proprioceptive salience was enhanced using an ankle weight. We hypothesised that this would increase congruency between internal focus instructions and movement production.
Results
Experiments 1 and 2 revealed reduced amplitude errors under an internal focus whilst Experiment 3 showed similar findings with the addition of lower EMG activity when adopting an internal focus. Movement variability findings were indicative of enhanced planning.
Conclusions
When pertinence of proprioceptive information was amplified, benefits of an internal focus were more pronounced and performance was higher. Participants were better able to focus on movement characteristics to process proprioceptive feedback: something not afforded under an external focus. This raises doubts regarding the rigidity of the constrained action hypothesis.
... In addition, removing visual feedback results in slower reaction times (Khan, Elliott, Coull, Chua, & Lyons, 71 2002) and decreased endpoint accuracy (Chua & Elliott, 1993;Heath, 2005;Heath, Westwood, & 72 Binsted, 2004;Khan et al., 2002) in reaching. These results show that obstacle avoidance is sensitive to 73 many factors such as sensory accuracy, systemic noise (i.e. ...
When reaching to a visual target, humans need to transform the spatial target representation into the coordinate system of their moving arm. It has been shown that increased demands in such coordinate transformations, for instance when the head is rolled toward one shoulder, lead to higher movement variability and influence movement decisions. However, it is unknown whether the brain incorporates such added variability to adjust movements when it is necessary. We designed an obstacle avoidance task in which participants had to reach to a visual target without colliding with an obstacle. We introduced different coordinate transformation demands by varying head roll (straight, 30° clockwise and 30° counterclockwise). In agreement with previous studies, we observed that the reaching variability increased when the head was tilted. In addition, participants systematically changed their obstacle avoidance behavior with head roll. In particular, they changed the preferred direction of passing the obstacle and increased the error margins indicated by stronger movement curvature. Indeed, reaching movements did not differ in the number of collisions between the head roll and the head straight conditions. These results suggest that the brain takes the added movement variability during head roll into account and compensates for it by adjusting the reaching trajectories.
... However, online adjustments can also arise early in a trajectory through the comparison of expected-to-actual sensory consequences of the movement (Desmurget and Grafton 2000;Elliott et al. 1991;Grierson and Elliott 2008;Scott 2016). Offline control occurs prior to movement onset, and involves using prior information regarding the outcome of previously completed movements in the planning of an upcoming movement (Elliott and Allard 1985;Elliott et al. 2004;Hansen et al. 2006;Khan et al. 2002Khan et al. , 2003Zelaznik et al. 1983). ...
Human movements are remarkably adaptive. We are capable of completing movements in a novel visuomotor environment with similar accuracy to those performed in a typical environment. In the current study, we examined if the control processes underlying movements under typical conditions were different from those underlying novel visuomotor conditions. 16 participants were divided into two groups, one receiving continuous visual feedback during all reaches (CF), and the other receiving terminal feedback regarding movement endpoint (TF). Participants trained in a virtual environment by completing 150 reaches to three targets when (1) a cursor accurately represented their hand motion (i.e., typical environment) and (2) a cursor was rotated 45° clockwise relative to their hand motion (i.e., novel environment). Analyses of within-trial measures across 150 reaching trials revealed that participants were able to demonstrate similar movement outcomes (i.e., movement time and angular errors) regardless of visual feedback or reaching environment by the end of reach training. Furthermore, a reduction in variability across several measures (i.e., reaction time, movement time, time after peak velocity, and jerk score) over time showed that participants improved the consistency of their movements in both reaching environments. However, participants took more time and were less consistent in the timing of initiating their movements when reaching in a novel environment compared to reaching in a typical environment, even at the end of training. As well, angular error variability at different proportions of the movement trajectory was consistently greater when reaching in a novel environment across trials and within a trial. Together, the results suggest a greater contribution of offline control processes and less effective online corrective processes when reaching in a novel environment compared to when reaching in a typical environment.
... Moreover, we also observed higher wrist velocities in VH compared to H (Fig. 3c). These advantages suggest that movements were influenced by the available sensory information already prior to the start of the movement: having both visual and haptic information about the target object led to faster movements [50][51][52][53] . Interestingly, this movement rapidity did not hinder performance, quite the contrary, the MGA reduction suggests that the joint visuo-haptic information actually optimized grasping movements. ...
Grasping movements are typically performed toward visually sensed objects. However, planning and execution of grasping movements can be supported also by haptic information when we grasp objects held in the other hand. In the present study we investigated this sensorimotor integration process by comparing grasping movements towards objects sensed through visual, haptic or visuo-haptic signals. When movements were based on haptic information only, hand preshaping was initiated earlier, the digits closed on the object more slowly, and the final phase was more cautious compared to movements based on only visual information. Importantly, the simultaneous availability of vision and haptics led to faster movements and to an overall decrease of the grip aperture. Our findings also show that each modality contributes to a different extent in different phases of the movement, with haptics being more crucial in the initial phases and vision being more important for the final on-line control. Thus, vision and haptics can be flexibly combined to optimize the execution of grasping movement.
... stroke survivors were longer than controls, yet, in terms of the variability, the stroke survivors showed higher variability mainly in the paretic limb. When we considered the spatial variability of the cursor (i.e., the object that was controlled in both unimanual and bimanual tasks) in the direction perpendicular to the reach, we found that, consistent with prior studies (Khan et al. 2002), the variability showed a distinct pattern during the reach; this was characterized by low variability at the start and end of the movemen, and peak variability occurring at~50% into the movement. This variability profile of the cursor was also reflected in the variability of the arm in unimanual tasks because there was no redundancy in the unimanual task. ...
Stroke often results in hemiparesis, leaving one side of the body "affected" relative to the other side. Prior research has shown that the affected arm has higher variability; however, the extent to which this variability can be modulated is unclear. Here we used a shared bimanual task to examine the degree to which participants could modulate the variability in the affected arm after stroke. Participants with chronic stroke ( n = 11) and age-matched controls ( n = 11) performed unimanual and bimanual reaching movements to move a cursor on a screen to different targets. In the unimanual condition, the cursor was controlled only by the movement of a single arm, whereas, in the bimanual condition, the cursor position was "shared" between the two arms by using a weighted average of the two hand positions. Unknown to the participants, we altered the weightings of the affected and unaffected arms to cursor motion and examined how the movement variability on each arm changed depending on its contribution to the task. Results showed that stroke survivors had higher movement variability on the affected arm; however, like age-matched controls, they were able to modulate the variability in both the affected and unaffected arms according to the weighting condition. Specifically, as the weighting on a particular arm increased (i.e., it became more important to the task), the movement variability decreased. These results show that stroke survivors are capable of modulating variability depending on the task context, and this feature may potentially be exploited for rehabilitation paradigms. NEW & NOTEWORTHY We show that chronic stroke survivors, similar to age-matched controls, are able to modulate variability in their affected and unaffected limbs in redundant bimanual tasks as a function of how these limbs contribute to the task. Specifically, in both affected and unaffected limbs, the variability of the limb increases as its contribution to the task decreases. This feature may potentially be exploited in rehabilitation paradigms using bimanual tasks.
... The higher relative frequency of one of two types of trials goes along with a higher number of repetitions, and repetitions typically facilitate performance (cf. Cheng, Luis, & Tremblay, 2008;Khan, Elliott, Coull, Chua, & Lyons, 2002;Kirby, 1980;Song & Nakayama, 2007;Zelaznik, Hawkins, & Kisselburgh, 1983). Notably, as compared with alternations between two types of trials, repetitions of one type facilitate the selective processing of individual stimulus features. ...
In a cursor-control task, the sensed positions of cursor and hand are biased toward each other. We previously found different characteristics of implicit and explicit measures of the bias of sensed hand position toward the position of the cursor, suggesting the existence of distinct neural representations. Here we further explored differences between the two types of measure by varying the proportions of trials with explicit hand-position (H) and cursor-position (C) judgments (C20:H80, C50:H50, and C80:H20). In each trial, participants made a reaching movement to a remembered target, with the visual feedback being rotated randomly, and subsequently they judged the hand or the cursor position. Both the explicitly and implicitly measured biases of sensed hand position were stronger with a low proportion (C80:H20) than with a high proportion (C20:H80) of hand-position judgments, suggesting that both measures place more weight on the sensory modality relevant for the more frequent judgment. With balanced proportions of such judgments (C50:H50), the explicitly assessed biases were similar to those observed with a high proportion of cursor-position judgments (C80:H20), whereas the implicitly assessed biases were similar to those observed with a high proportion of hand-position judgments (C20:H80). Because strong weights of cursor-position or hand-position information may be difficult to increase further but are easy to reduce, the findings suggest that the implicit measure of the bias of sensed hand position places a relatively stronger weight on proprioceptive hand-position information, which is increased no further by a high proportion of hand-position judgments. Conversely, the explicit measure places a relatively stronger weight on visual cursor-position information.
... When vision was not available, or there was uncertainty about its availability, the aiming trajectories were more symmetric indicating less online control based on vision. When participants know vision will be available they also spend less time preparing their movements (i.e., shorter reaction times; Burkitt et al., 2013;Khan et al., 2002). ...
Recently our group forwarded a model of speed-accuracy relations in goal-directed reaching. A fundamental feature of our multiple process model was the distinction between two types of online regulation: impulse control and limb-target control. Impulse control begins during the initial stages of the movement trajectory and involves a comparison of actual limb velocity and direction to an internal representation of expectations about the limb trajectory. Limb-target control involves discrete error-reduction based on the relative positions of the limb and the target late in the movement. Our model also considers the role of eye movements, practice, energy optimization and strategic behavior in limb control. Here, we review recent work conducted to test specific aspects of our model. As well, we consider research not fully incorporated into our earlier contribution. We conclude that a slightly modified and expanded version of our model, that includes crosstalk between the two forms of online regulation, does an excellent job of explaining speed, accuracy, and energy optimization in goal-directed reaching.
... In addressing this question, we have drawn on work contrasting reaching/grasping movements performed with (i.e., closed-loop action) and without (i.e., open-loop) continuous limb and target vision across blocked and random feedback schedules. In particular, results have shown that closed-loop trials performed in a blocked feedback schedule are more accurate (Zelaznik et al., 1983;Elliott and Allard, 1985), exhibit more online trajectory amendments (Khan et al., 2002) and produce more effective PGAs (Jakobson and Goodale, 1991) than counterparts performed in a random feedback schedule. Accordingly, the inability to predict the availability of visual feedback has been interpreted to reflect the adoption of a ''worst-case'' control strategy wherein a response is specified largely in advance of movement execution via central planning mechanisms (Elliott et al., 2009). ...
An emerging issue in movement neurosciences is whether haptic feedback influences the nature of the information supporting a simulated grasping response (i.e., pantomime-grasping). In particular, recent work by our group contrasted pantomime-grasping responses performed with (i.e., PH+ trials) and without (i.e., PH- trials) terminal haptic feedback in separate blocks of trials. Results showed that PH- trials were mediated via relative visual information. In contrast, PH+ trials showed evidence of an absolute visuo-haptic calibration – a finding attributed to an error signal derived from a comparison between expected and actual haptic feedback (i.e., an internal forward model). The present study examined whether advanced knowledge of haptic feedback availability influences the aforementioned calibration process. To that end, PH- and PH+ trials were completed in separate blocks (i.e., the feedback schedule used in our group’s previous study) and a block wherein PH- and PH+ trials were randomly interleaved on a trial-by-trial basis (i.e., random feedback schedule). In other words, the random feedback schedule precluded participants from predicting whether haptic feedback would be available at the movement goal location. We computed just-noticeable-difference (JND) values to determine whether responses adhered to, or violated, the relative psychophysical principles of Weber’s law. Results for the blocked feedback schedule replicated our group’s previous work, whereas in the random feedback schedule PH- and PH+ trials were supported via relative visual information. Accordingly, we propose that a priori knowledge of haptic feedback is necessary to support an absolute visuo-haptic calibration. Moreover, our results demonstrate that the presence and expectancy of haptic feedback is an important consideration in contrasting the behavioral and neural properties of natural and stimulated (i.e., pantomime-grasping) grasping.
... The primary movement corresponds to the initial pulse toward the vicinity of target. Although this preprogrammed movement phase is traditionally associated with open-loop control (Woodworth 1899), recent work has shown that vision is being used more continuously for the planning and control of limb movements (i.e., impulse control; see also Heath 2005;Khan et al. 2002Khan et al. , 2006Saunders and Knill 2003). While corrections may occur very early in the movement, the main body of closed-loop control takes place during the homing-in phase. ...
The present study examines whether non-active older adults are more dependent on visual information when executing aiming movements, and whether age-related declines in proprioception play a mediating role herein. Young (N=40) and older adults (N=38) were divided into physically active and non-active subgroups based on self-reported sports participation levels. In Experiment 1, participants executed wrist-aiming movements with and without visual feedback. In Experiment 2, passive proprioceptive acuity was assessed using wrist motion detection and position matching tests. Results showed similar aiming accuracy across age groups both with and without visual feedback, but older adults exhibited longer movement times, prolonged homing-in phase, and made more corrective submovements. Passive proprioceptive acuity was significantly affected by physical activity level and age, with participants in the active group scoring better than their non-active peers. However, these declines did not predict performance changes on the aiming task. Taken together, our observations suggest that decline in proprioceptive acuity did not predict performance changes on the aiming task and older adults were able to compensate for their decreased motion and position sense when allowed sufficient time. In line with these observations, we proposed that older adults are able to compensate for their decline in proprioception by increasing their reliance on predictive models.
... Second, by providing advance knowledge on target location, it is possible to rely more on pre-planning of movement kinematics, which is then reXected in less need for on-line control and a reduction in movement time (Borysiuk and Sadowski 2007). However, it is important to note that a distinction has to be made between self-paced motor tasks, in which participants are typically instructed to act as quickly and accurately as they deem possible (Elliott and Allard 1985;Khan et al. 1998Khan et al. , 2002, and externally paced tasks such as interceptive actions, which require a speciWc spatiotemporal relationship between the approach object and responding eVector to be established and maintained. As a consequence of these diVerent timing constraints (i.e., internally vs. externally imposed), aiming for stationary objects is prone to a speedaccuracy trade-oV, whereby there is a shift in the amount that movement kinematics are planned in advance or adjusted on-line. ...
The purpose of this experiment was to examine the eVects of advance knowledge on the kinematics of one-handed catching. Balls were launched from a distance of 8.4 m by a ball-projection machine with adjustable launching speed. Fifteen skilled ball catchers caught 160 balls with their preferred hand under blocked-order (4 blocks, each comprising 20 trials at 1 of 4 diVerent ball speeds) or random-order (4 blocks, each comprising 20 trials of 4 diVerent ball speeds) conditions. By projecting balls with diVerent ball speeds from a Wxed position, it was possible to modify the temporal constraints of the catching task. In both the blocked-order and random-order conditions, catching performance (number of catches, touches and misses) decreased with increasing temporal constraints. Analysis of successful trials indicated that this equal level of catching performance was achieved with diVerent movement kine-matics. SpeciWcally, there was a change in movement time, latency, wrist velocity proWle, and coeYcient of straight-ness. Based on expectancy of previous trials, movement kinematics was scaled to ball speed in the blocked-order condition whereas in the random-order condition, participants exhibited a more default initial response. However, this latter mode of control was functional in that it increased the likelihood of success for the higher ball speeds while also providing participants with a larger temporal window to negotiate the unexpected temporal constraint on-line for the lowest ball speed.
... In turn, we argue that this 'prioritizing' of the last-placed location may lead to a smaller chance of a target undershoot compared to a more typical aiming circumstance, such as in the no-placeholder condition. This conjecture is supported by previous evidence of movement endpoint locations being strongly influenced by the pre-planning processes that follow the reinforcement of upcoming trial proceedings (i.e., prior knowledge) (Elliott et al. 2014;Khan et al. 2002Khan et al. , 2006b. Though this proposal is consistent with the idea that the violation reflects a strategic movement bias, the nature of the bias is quite different from the one suggested by Glazebrook et al. (2015). ...
Fitts’ Law holds that, to maintain accuracy, movement times of aiming movements must change as a result of varying degrees of movement difficulty. Recent evidence has emerged that aiming to a target located last in an array of placeholders results in a shorter movement time than would be expected by the Fitts’ equation – a violation of Fitts’ Law. It has been suggested that the violation emerges because the performer adopts an optimized movement strategy in which they partially pre-plan an action to the closest placeholder (undershoot the last placeholder) and rely on a secondary acceleration to propel the limb toward the last location when it is selected as the target (Glazebrook et al., Hum Mov Sci, 39:163-176, 2015). In the current study, we examine this proposal and further elucidate the processes underlying the violation by examining limb displacement and corrective submovements that occur when performers aim to different target locations. For our Main Study, participants executed discrete aiming movements in a five-placeholder array. We also reanalysed data from a previously reported study in which participants aimed in placeholder and no placeholder conditions (Blinch et al., Exp Brain Res, 223: 505-515, 2012). The results showed the violation of Fitts’ Law unfolded following peak velocity (online control). Further, the analysis showed that movements to the last target tended to overshoot and had a higher proportion of secondary submovements featuring a reversal than other categories of submovement (secondary accelerations, discontinuities). These findings indicate that the violation of Fitts’ Law may, in fact, result from a strategic bias towards planning farther initial displacements of the limb which accommodates a shorter time in online control.
... Because the way the movement is performed changes when vision is removed, for example, an increase in speed in traversing the balance beam, it has been argued that experts are flexible in their ability to use other sources of feedback to control their movement, rather than perform in a programmed fashion. Indeed, knowledge as to whether vision will be available during practice or performance affects the movement-control strategies that participants adopt (see Khan, Elliot, Coull, Chua, & Lyons, 2002). If performance is required under consistent sensory conditions, then it is likely that a reliance on this sensory information will be seen as a function of practice and increasing skill. ...
The purpose of the present study was to examine errors for an isometric goal-directed aiming task during familiarization at different hand orientation. Interaction between neutral and pronated hand orientations with and without directional feedback would provide insights into short-term adaptations and the nature of control. In this study, 30 healthy right-handed adults (age, 22.7 ± 3.1 years; weight, 69.4 ± 16.6 kg; height, 166.7 ± 7.9 cm) were randomly assigned to neutral or pronated hand orientation conditions. To assess familiarization, participants performed ten sets (16 targets/set) of goal-directed aiming task with continuous visual feedback towards targets symmetrically distributed about the origin. Following familiarization, participants then completed eight sets; four sets with and four sets without directional feedback, in an alternated order. For both hand orientations, directional errors were reduced in the first two sets (p < 0.05), suggesting only three sets were required for familiarization. Additionally, the learning rate was also similar for both hand orientations. Following familiarization, aiming errors without feedback were significantly higher than with feedback while no change between sets was observed, regardless of hand orientation. Aiming errors were reduced in the early phase with and without visual feedback, however, in the late phase, errors were corrected when visual feedback was provided. It suggests that hand orientation does not affect familiarization, and mechanisms similar to rapid learning may be involved. It is probable that learning is consolidated during familiarization along with feedforward input to maintain performance. In addition, proprioceptive feedback plays a role in reducing errors early, while the online visual feedback plays a role in reducing errors later, independent of hand orientation.
It is well known that vision makes an important contribution to the control of goal-directed movements. However, task performance can be maintained when vision is interrupted, such as when a goalkeeper faces a free kick in soccer and the ball moves behind teammates and opposing players. To maintain behavior, it is necessary to process the visual information available from intermittent samples. In this review, we consider the performance and learning effects of intermittent vision in tasks such as aiming, reaching and grasping, goal-directed locomotion and ball-catching. We review research that finds both interocular and intraocular integration contribute to continuous upper limb control with intermittent visual pickup/sampling. Recent work using intermittent visual presentation (i.e., stroboscopic vision) to facilitate learning of general and task-specific visual-motor skills indicates that training/learning protocols that challenge, but don’t alter, the visual-motor processing associated with a specific visual-motor task can be effective. In this theoretical context, we discuss methodological and design factors that could impact the effectiveness of future training studies.
Reaches with overlapping stimulus-response spatial relations (propointing) adhere to speed–accuracy relations as defined by Paul Fitts’ index of difficulty equation (ID Fitts : in bits of information). This movement principle is attributed to response mediation via the “fast” visuomotor networks of the dorsal visual pathway. It is, however, unclear whether the executive demands of dissociating stimulus-response spatial relations by reaching mirror-symmetrical to a target (antipointing) elicits similar adherence to Fitts’ equation. Here, pro- and antipointing responses were directed to a constant target amplitude with varying target widths to provide ID Fitts values of 3.0, 3.5, 4.3, and 6.3 bits. Propointing movement times linearly increased with ID Fitts —a result attributed to visually based trajectory corrections. In contrast, antipointing movement times, deceleration times, and endpoint precision did not adhere to Fitts’ equation. These results indicate that antipointing renders a “slow” and offline mode of control mediated by the visuoperceptual networks of the ventral visual pathway.
Investigations of visually-guided target-directed movement frequently adopt measures of within-participant spatial variability to infer the contribution of planning and control. The present study aims to verify this current trend by exploring the distribution of displacements at kinematic landmarks with a view to understanding the potential sources of variability. Separate sets of participants aiming under full visual feedback conditions revealed a comparatively normal distribution for the displacements at peak velocity and movement end. However, there was demonstrable positive skew in the displacement at peak acceleration and a significant negative skew at peak deceleration. The ranges of the distributions as defined by either ±1SD or ±34.13th percentile (equivalent to an estimated 68.26% of responses) also revealed differences at peak deceleration. These findings indicate that spatial variability in the acceleration domain features highly informative systematic, as well as merely inherent, sources of variability. Implications for the further quantification of trial-by-trial behaviour are discussed.
We sought to determine whether a putative lower-visual field (loVF) advantage for projections to the visuomotor networks of the dorsal visual pathway influences online reaching control. Participants reached to 3-dimensional depth targets presented in the loVF and upper-visual field (upVF) in binocular and monocular visual conditions, and when online vision was available (i.e., closed-loop) or unavailable (i.e., open-loop). To examine the degree to which responses were controlled online we computed the proportion of variance (R2) explained by the spatial position of the limb at distinct stages in the reaching trajectory relative to a response's ultimate movement endpoint. Results showed that binocular and closed-loop reaches exhibited shorter movement times and more online corrections (i.e., smaller R2 values) than their monocular and open-loop counterparts. Notably, however, loVF and upper-visual field reaches exhibited equivalent performance metrics across all experimental conditions. Accordingly, results provide no evidence of a loVF advantage for online reaching control to 3-dimensional targets.
Skilled sensorimotor interactions with the world result from a series of decision-making processes that determine, on the basis of information extracted during the unfolding sequence of events, which movements to make and when and how to make them. Despite this inherent link between decision-making and sensorimotor control, research into each of these two areas has largely evolved in isolation, and it is only fairly recently that researchers have begun investigating how they interact and, together, influence behaviour. Here, we review recent behavioural, neurophysiological and computational research that highlights the role of decision-making processes in the selection, planning and control of goal-directed movements in humans and nonhuman primates.
A major challenge to the measurement of online control is the contamination by offline, planning-based processes. The current study examined the sensitivity of four measures of online control to offline changes in reaching performance induced by prism adaptation and terminal feedback. These measures included the squared Z scores (Z2) of correlations of limb position at 75% movement time versus movement end, variable error, time after peak velocity, and a frequency-domain analysis (pPower). The results indicated that variable error and time after peak velocity were sensitive to the prism adaptation. Furthermore, only the Z2values were biased by the terminal feedback. Ultimately, the current study has demonstrated the sensitivity of limb kinematic measures to offline control processes and that pPower analyses may yield the most suitable measure of online control.
Introduction: Motor skill acquisition studies have shown that the performance of a motor task will be smoother after practice; however, the type of practice is very important. Thus, the aim of this study was to investigate the effect of practice with task-specific instability on performance and acquisition of a throwing skill.
Materials and Methods: This quasi-experimental study was conducted on 16 semi-skilled subjects under 2 practice conditions, with and without availability of visual feedback. Each practice stage involved 3 blocks of 10 trials. The subjects’ throwing skill was evaluated in pretest and posttests, before and after the practicing stages. Two repeated measures ANOVA and paired t-test were used to examine the differences between subjects in practicing and test stages at a significance level of 0.05.
Results: No significant difference were observed between practice blocks in the two stages of practice; however, there were significant differences between pretest and posttest with blocks in the second stage (P = 0.001). Moreover, no significant differences were observed between the posttests of the two practice stages.
Conclusion: Task-specific instability with blocking of visual feedback not only induces the acquisition of complex motor skills, but also prepares the individual for confronting unstable conditions. It is suggested that coaches and therapists train athletics and patients for performing complex skills under unstable conditions to better prepare them for confronting these conditions.
Movement planning consists of choosing the intended endpoint of the movement and selecting the motor program that will bring the effect or on the endpoint. It is widely accepted that movement endpoint is updated on a trial-by-trial basis with respect to the observed errors and that the motor program for a given movement follows the rules of optimal feedback control. In this article, we show clear limitations of these theories. First, participants in the current study could not tune their motor program appropriately for each individual trial. This was true even when the participants selected the width of the target that they reached toward or when they had learned the appropriate motor program previously. These data are compatible with the existence of a switching cost for motor planning, which relates to the drop in performance due to an imposed switch of motor programs. This cost of switching shares many features of costs reported in cognitive task switching experiments and, when tested in the same participants, was correlated with it. Second, we found that randomly changing the width of a target over the course of a reaching experiment prevents the motor system from updating the endpoint of movements on the basis of the performance on the previous trial if the width of the target has changed. These results provide new insights into the process of motor planning and how it relates to optimal control theory and to an action selection based on the reward consequences of the motor program rather than that based on the observed error.
Pressure to perform often results in decrements to both outcome accuracy and the kinematics of motor skills. Furthermore, this pressure–performance relationship is moderated by the amount of accumulated practice or the experience of the performer. However, the interactive effects of performance pressure and practice on the underlying processes of motor skills are far from clear. Movement execution involves both an offline pre-planning process and an online control process. The present experiment aimed to investigate the interaction between pressure and practice on these two motor control processes. Two groups of participants (control and pressure; N = 12 and 12, respectively) practiced a video aiming amplitude task and were transferred to either a non-pressure (control group) or a pressure condition (pressure group) both early and late in practice. Results revealed similar accuracy and movement kinematics between the control and pressure groups at early transfer. However, at late transfer, the introduction of pressure was associated with increased performance compared to control conditions. Analysis of kinematic variability throughout the movement suggested that the performance increase was due to participants adopting strategies to improve movement planning in response to pressure reducing the effectiveness of the online control system.
Goal-directed aiming movements are planned and executed so that they optimize speed, accuracy and energy expenditure. In particular, the primary submovements involved in manual aiming attempts typically undershoot targets in order to avoid costly time and energy overshoot errors. Furthermore, in aiming movements performed over a series of trials, the movement planning process considers the sensory information associated with the most recent aiming attempt. The goal of the current study was to gain further insight into how the sensory consequences associated with the recent and forthcoming aiming attempts impact performance. We first examined whether performers are more conservative in their aiming movements with a heavy, as opposed to a light, stylus by determining whether primary submovements undershot the target to a greater extent in the former due to an anticipated increase in spatial variability. Our results show that movements with the heavy stylus demonstrated greater undershoot biases in the primary submovements, as well as greater trial-to-trial spatial variability at specific trajectory kinematic landmarks. In addition, we also sought to determine whether the sensory information experienced on a previous aiming movement affected movement planning and/or online control on the subsequent aiming attempt. To vary the type sensory consequences experienced on a trial-to-trial basis, participants performed aiming movements with light and heavy styli in either blocked or random orderings of trials. In the random-order conditions, some participants were provided advance information about stylus mass for the upcoming trial, while others were not. The blocked and random trial orders had minimal impacts on end point aiming performance. Furthermore, similarities in the times to key kinematic landmarks in the trajectories of the random-order groups suggest that recent trial experience had a greater effect on the upcoming aiming movement compared with advance task knowledge.
Previous studies on how we hit moving targets have revealed that the direction in which we move our hand is continuously adjusted
on the basis of the target’s perceived position, with a delay of about 110 ms. In the present study we show that the acceleration
of the hand is also under such continuous control. Subjects were instructed to hit moving targets (running spiders) as quickly
as possible with a rod. We found that changing the velocity of the target influenced the speed with which the rod was moved.
The influence was noticeable about 200 ms after the target’s velocity changed. The extent of the influence was consistent
with a direct dependence of the acceleration of the hand on the target’s velocity. We conclude that the acceleration of the
hand is continuously adjusted on the basis of the speed of the target, with a delay of about 200 ms.
A stochastic optimized-submovement model is proposed for Fitts' law, the classic logarithmic trade-off between the duration and spatial precision of rapid aimed movements. According to the model, an aimed movement toward a specified target region involves a primary submovement and an optional secondary corrective submovement. The submovements are assumed to be programmed such that they minimize average total movement time while maintaining a high frequency of target hits. The programming process achieves this minimization by optimally adjusting the average magnitudes and durations of noisy neuromotor force pulses used to generate the submovements. Numerous results from the literature on human motor performance may be explained in these terms. Two new experiments on rapid wrist rotations yield additional support for the stochastic optimized-submovement model. Experiment 1 revealed that the mean durations of primary submovements and of secondary submovements, not just average total movement times, conform to a square-root approximation of Fitts' law derived from the model. Also, the spatial endpoints of primary submovements have standard deviations that increase linearly with average primary-submovement velocity, and the average primary-submovement velocity influences the relative frequencies of secondary submovements, as predicted by the model. During Experiment 2, these results were replicated and extended under conditions in which subjects made movements without concurrent visual feedback. This replication suggests that submovement optimization may be a pervasive property of movement production. The present conceptual framework provides insights into principles of motor performance, and it links the study of physical action to research on sensation, perception, and cognition, where psychologists have been concerned for some time about the degree to which mental processes incorporate rational and normative rules.
Measured the short-term retention of force responses in undergraduate volunteers. The dependent variables were the absolute and algebraic errors made by S in attempting to reproduce a criterion force during recall trials. In Exp. I (N = 20), retention was measured over 5 unfilled intervals ranging 4-6 sec. Forgetting, i.e., an increase in errors, was not found. Exp. II (N = 24) was a partial replication of Exp. I, except that during 1/2 of the retention intervals, S counted backwards. The result was a decrease in error over a 30-sec retention interval for both filled and unfilled conditions. Significantly larger errors were associated with the filled condition. In Exp. III (N = 24), the recall response shifted toward the relative magnitude of an interpolated force to the criterion force. The increase in error associated with filled retention intervals was successfully replicated. For Exp. IV (N = 27), successive repetitions of the criterion force prior to the recall trial produced an increase, not decrease, in error at recall. All 4 experiments were characterized by overshooting response sets (positive algebraic errors) at recall. Detailed comparisons with available data from earlier motor short-term memory (STM) studies indicate a set of consistent findings across the earlier and present studies, although apparent differences in memory functions were obtained. Consistencies were, with respect to the directional shifts, occurring in the algebraic error scores as a function of various independent variables. The different memory functions 200 215 231 231 231 296 379 413 43823142334 different response sets with these algebraic error shifts. A dual process theory of motor STM, incorporating decay and interference features, is advanced to account for the set of findings, and similarities with dual process theories of verbal STM are noted. (28 ref.)
DETERMINED THE MINIMUM AMOUNT OF TIME NECESSARY TO PROCESS VISUAL FEEDBACK FROM A MOVEMENT. 8 STUDENTS RAPIDLY MOVED A STYLUS FROM A HOME POSITION TO A TARGET. ON 1/2 THE TRIALS ALL LIGHTS TURNED OFF AT THE START OF THE MOVEMENT SO THAT THEY WERE MADE IN THE DARK. VISUAL FEEDBACK DID NOT FACILITATE ACCURACY IN HITTING THE TARGET WHEN THE MOVEMENT WAS AS SHORT AS 190 MSEC. FOR DURATIONS OF 260 MSEC. OR LONGER, HAVING THE LIGHTS ON FACILITATED ACCURACY, SUGGESTING THAT IT TAKES 190-260 MSEC. TO PROCESS THE FEEDBACK.
Ss were presented with spiders running from left to right at various velocities over a structured background. Motion of the background influenced the perceived velocity of the spider: Motion of the background in the opposite direction than the spider increased the perceived velocity. The perceived position of the spider was not influenced by background motion. Ss were asked to hit the spiders as quickly as possible. Fast spiders were hit with a higher velocity than slow spiders. The same effect was found if the spiders only differed in apparent velocity, induced by motion of the background. The trajectory of the hit was not influenced by motion of the background. The authors concluded that although velocity is nothing but the change of position in time, velocity and position are processed independently. Furthermore, these two separately processed sources of information are used in both perception and action.
It is well known that dynamic visual information influences movement control, whereas the role played by background visual information is still largely unknown. Evidence coming mainly from eye movement and manual tracking studies indicates that background visual information modifies motion perception and might influence movement control. The goal of the present study was to test this hypothesis. Subjects had to apply pressure on a strain gauge to displace in a single action a cursor shown on a video display and to immobilize it on a target shown on the same display. In some instances, the visual background against which the cursor moved was unexpectedly perturbed in a direction opposite to (Experiment 1), or in the same direction as (Experiment 2) the cursor controlled by the subject. The results of both experiments indicated that the introduction of a visual perturbation significantly affected aiming accuracy. These results suggest that background visual information is used to evaluate the velocity of the aiming cursor, and that this perceived velocity is fed back to the control system, which uses it for on-line corrections.
In 1899, R. S. Woodworth published a seminal monograph, "The Accuracy of Voluntary Movement." As well as making a number of important empirical contributions, Woodworth presented a model of speed-accuracy relations in the control of upper limb movements. The model has come to be known as the two-component model because the control of speeded limb movements was hypothesized to entail both a central and a feedback-based component. Woodworth's (1899) ideas about the control of rapid aiming movements are evaluated in the context of current empirical and theoretical contributions.
Two experiments are reported in which the effects of different levels of spatial variability of the initial phase of aiming movements were explored. It was found that longer, faster, and more spatially variable initial sub movements were associated with an almost proportional increase in the distance between the average location at which the first submovement ended and the target. The first experiment involved a multisegmental arm motion that required a direction reversal, in which spatial variability could be estimated in all three dimensions. The second was a unidirectional, one-degree-of-freedom wrist supination task. The variability-amplitude relationship for the initial submovement was present in both. It is argued that the variability, or unpredictability, of the initial submovement is a determinant of its average amplitude, such that initial submovements approach the target as closely as is permitted by the level of variability. Such a mechanism allows task constraints such as accuracy requirements and allowable error rates to be met most efficiently, in a manner similar to the recently described optimization of submovement durations. If this mechanism is a general, ubiquitous phenomenon in rapid aiming, certain features of its internal kinematic structure are predictable. A set of five such predictions is outlined.
A major line of behavioral support for motor-program theory derives from evidence indicating that feedback does not influence the execution and control of limited duration movements. Since feedback cannot be utilized, the motor-program is assumed to act as the controlling agent. in a classic study, Keele and Posner observed that visual feedback had no effect on the accuracy of 190-msec single-aiming movements. Therefore visual feedback processing time is greater than 190 msec, and, more importantly, limited duration movements are governed by motor programs. In the present paper, we observed that visual feedback can affect the spatial accuracy of movement with durations much less than 190 msec. We hypothesize that visual feedback can aid motor control via processes not associated with intermittent error corrections.
In 1899, R. S. Woodworth published a seminal monograph, "The Accuracy of Voluntary Movement." As well as making a number of important empirical contributions, Woodworth presented a model of speed-accuracy relations in the control of upper limb movements. The model has come to be known as the two-component model because the control of speeded limb movements was hypothesized to entail both a central and a feedback-based component. Woodworth's (1899) ideas about the control of rapid aiming movements are evaluated in the context of current empirical and theoretical contributions.
It is well known that dynamic visual information influences movement control, whereas the role played by background visual information is still largely unknown. Evidence coming mainly from eye movement and manual tracking studies indicates that background visual information modifies motion perception and might influence movement control. The goal of the present study was to test this hypothesis. Subjects had to apply pressure on a strain gauge to displace in a single action a cursor shown on a video display and to immobilize it on a target shown on the same display. In some instances, the visual background against which the cursor moved was unexpectedly perturbed in a direction opposite to (Experiment 1), or in the same direction as (Experiment 2) the cursor controlled by the subject. The results of both experiments indicated that the introduction of a visual perturbation significantly affected aiming accuracy. These results suggest that background visual information is used to evaluate the velocity of the aiming cursor, and that this perceived velocity is fed back to the control system, which uses it for on-line corrections.
The purpose of this experiment was to investigate how the control of aiming movements performed as fast and as accurately as possible changes with practice. We examined: (1) the influence of visual feedback on the initial impulse and error correction phases of aiming movements during acquisition; and (2) the effect of removing visual feedback at different levels of practice. Results from the acquisition trials indicated that vision had a major impact on the organization of the initial impulse and error correction phases. Also, consistent with findings from research involving temporally constrained movements, the cost of removing vision was greater after extensive levels than after moderate levels of practice. Collectively, these results denote the importance of visual feedback to the learning of this particular class of aiming movements. Learning appears to be a dual process of improved programming of the initial impulse and increased efficiency of feedback processing. Practice not only acts on programming and feedback processes directly, but also indirectly through a reciprocal interplay between these two processes.
focused primarily on the potential role played by visual information regarding a self-performed ongoing movement under normal afference / selectively review some studies in which the availability of visual information for the control of various types of movement has been manipulated
report some of the results obtained in various types of aiming tasks, as well as in the "ball catching" task / focus on the results obtained by researchers who have used a transfer paradigm to assess the effects of different sources of afference on movement learning and control
shed some new light on the role played by visual information for movement control as a particular individual's expertise increases / shown that withdrawing a source of information after extended practice caused a larger error than when that information was withdrawn after modest or moderate practice
propose a theoretical interpretation of the presented results (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Conducted 2 experiments to examine the influence of instructional set and vision on the kinematics and end-point accuracy of a simple target-aiming movement. 20 Ss with normal or corrected-to-normal vision were required to move a stylus from a home position to a target under various lighting conditions. While instructional set had a large impact on the velocity and acceleration patterns of the movements, the availability of vision before and during the movement was the best predictor of accuracy. Although Ss were more accurate in a full vision condition than in 2 visually degraded conditions, they made no more discrete adjustments to the movement trajectory. Data suggest that the visual control of aiming may occur in a continuous fashion. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Three experiments were conducted to examine the role of target information in manual aiming. The key manipulations in this experiment were the use of two target contexts (the two forms of the Mller-Lyer illusion) and the visual conditions under which subjects moved. In Experiment 1, we demonstrated that the inward- and outward-pointing arrows biased manual-aiming movements in a manner consistent with their well-known influence on perceptual judgements. The elimination of visual feedback during the aiming movement (Experiment 2), and visual information about the target-aiming layout prior to the movement (Experiment 3) increased the magnitude of the bias. Together, these results demonstrate the strong effect of target information on manual aiming, and specifically, on the movement-planning processes that precede movement.
Traditional models of visuomotor control have generally emphasized the importance of vision in the guidance of limb movements. Vision is thought to subserve the modificational processes underlying the control of these movements. The objectives of the present work were to elaborate upon the role of vision in the regulation of an ongoing limb movement, address issues pertaining to the nature of this regulation, and examine predictions of the Optimized Submovement Model (Meyer, Abrams, Kornblum, Wright and Smith 1988) of limb control. An aiming task was adopted in which subjects were required to displace a graphics cursor on a monitor toward a target. The presence of visual feedback proved to be a potent determinant of performance. In experiment 1, superior performance consistency with visual feedback was attribute to the prevalence of discrete and continuous modifications made to the movement when visual information was available. In experiment 2, the same visually-based performance advantage was found. However, this advantage was no longer related to the presence of adjustments to the movement. The present results are discussed with reference to current issues in the nature of visuomotor regulation and their implications toward the Optimized Submovement Model.
A number of recent models of limb control have attempted to explain speed-accuracy trade-off in goal-directed movements on the basis of the characteristics of the muscular impulses that are specified prior to movement initiation. In contrast, studies from our laboratory have demonstrated that, even for very rapid aiming movements, the characteristics of the movement trajectory change with the availability of visual information about the position of the limb and the target during the movement. Moreover, when the movement of the limb is perturbed at movement initiation by an electromagnetic force, performers can rapidly adjust their aiming movements in order to hit the target if visual feedback is available. The performer can also rapidly adjust to unexpected changes in target size and amplitude. Visually based adjustments to the movement trajectory can be either discrete or continuous.PsycINFO classification: 2330; 2343
An experiment was conducted to examine the hypothesis that the right hand system is superior in the processing of visual information. A manual aiming task utilizing four visual conditions was employed. In the full-vision (FV) condition subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off (AO) condition, the room lights were extinguished at movement initiation, thus preventing vision of the moving limb. The target remained illuminated. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. Ambient illumination and thus vision of the hand remained present. Finally there was a no-vision (NV) condition in which ambient illumination was removed and the target was extinguished upon initiation of the response movement. Although the manipulation of vision had potent effects upon terminal accuracy, and influenced reaction and movement time measures, the hands did not differ in the extent to which these characteristics were expressed. A left hand advantage for reaction time was observed. This may reflect a relative increase in right hemisphere involvement prior to aiming movements which are spatially complex.
The present paper reports a double-step analysis of a discrete aiming movement. A second target step was presented during the trajectory of the response to an initial step and represented an artificially induced movement error signal. Two stimulus patterns involving steps in the same direction (an undershoot error signal) and opposite direction (an overshoot error signal) to the initial step were examined. Moreover, in a random error condition the subject had no advance information regarding the direction of the error. In a deliberate error condition the subject knew in advance whether any subsequent error would be an undershoot or overshoot. Response parameters were considered as a function of the interstep interval which was randomly varied across trials. In terms of movement time, the standard deviations and a constant amendments score of double-step trials, subjects could respond more appropriately and effectively to a deliberate rather than a random error, and an undershoot error rather than an overshoot error. These results are discussed in terms of a mixed-mode of visuo-spatial error updating and related to the generalized motor program hypothesis.
Three experiments were conducted to determine whether a visual representation of the movement environment, useful for movement control, exists after visual occlusion. In Experiment 1 subjects moved a stylus to small targets in five different visual conditions. As in other studies (e.g. Elliott and Allard, 1985), subjects moved to the targets in a condition involving full visual information (lights on) and a condition in which the lights were extinguished upon movement initiation (lights off). Subjects also pointed to the targets under conditions in which the lights went off 2, 5 and 10 sec prior to movement initiation. While typical lights-on-lights-off differences in accuracy were obtained in this experiment (Keele and Posner, 1968), the more striking finding was the influence of the pointing delay on movement accuracy. Specifically, subjects exhibited a twofold increase in pointing error after only 2 sec of visual occlusion prior to movement initiation. In Experiment 2, we were able to replicate our 2-sec pointing delay effect with a between-subjects design, providing evidence that the results in Experiment 1 were not due to asymmetrical transfer effects. In a third experiment, the delay effect was reduced by making the target position visible in all lights-off situations. Together, the findings provide evidence for the existence of a brief (< 2 sec) visual representation of the environment useful in the control of aiming movements.
In this study, a visual target was localized by both limb and eye. The experimental procedure provided an opportunity to analyze the limb movement trajectories to the target whose location was displaced during saccades. Absence of visual information about position of the moving limb did not interfere with correction of the trajectory of pointing movements. These corrections reflect the new information about target position that becomes available at the end of the first saccade. Mean localization errors to stationary and to displaced targets were not significantly different. This result suggests that subjects were able to compare visual (retinal + eye position) information about the position of the target with information about the position of their moving limb derived from kinesthesis and/or efference copies of the motor commands. An analysis of velocity profiles indicates that the observed corrections of hand movement to target displacement could not be identified by an inflexion point in the trajectory. None of the subjects reported seeing the target change location. In other words, the motor command was adjustable despite the failure of changes in visual locus to reach consciousness.
Three experiments were conducted to determine how variables other than movement time influence the speed of visual feedback utilization in a target-pointing task. In Experiment 1, subjects moved a stylus to a target 20 cm away with movement times of approximately 225 msec. Visual feedback was manipulated by leaving the room lights on over the whole course of the movement or extinguishing the lights upon movement initiation, while prior knowledge about feedback availability was manipulated by blocking or randomizing feedback. Subjects exhibited less radial error in the lights-on/blocked condition than in the other three conditions. In Experiment 2, when subjects were forced to use vision by a laterally displacing prism, it was found that they benefited from the presence of visual feedback regardless of feedback uncertainty even when moving very rapidly (e.g. less than 190 msec). In Experiment 3, subjects pointed with and without a prism over a wide variety of movement times. Subjects benefited from vision much earlier in the prism condition. Subjects seem able to use vision rapidly to modify aiming movements but may do so only when the visual information is predictably available and/or yields an error large enough to detect early enough to correct.
IN experiments that used a pencil and graph paper targets, we have been able to demonstrate what we believe to be the intermittency of visual feedback control in a simple motor task. The intermittency hypothesis was first advanced by Craik1. It was developed by E. R. F. W. Grossman and P. J. Goodeve in their theoretical analysis of movement control (unpublished), showing that an intermittent servo mechanism could produce results obtained by Fitts and others that related the speed of movement to the terminal accuracy.
An experiment is reported which investigated the visual control of discrete rapid arm movements. Subjects were required to move as rapidly as possible to several target width-movement distance combinations under both visual and non-visual conditions. The movement time (MT) data were supportive of Fitts' Law in that MT was linearly related and highly correlated to the Index of Difficulty (ID). MT was also similar for different target width-distance combinations sharing the same ID value. The error rate analysis, which compared visual to non-visual perfromance, indicated that vision was only used, and to varying degrees, when MT exceeded 200 ms (3.58 ID level). There was some evidence that vision was differentially used within target width-distance combinations sharing the same ID. Estimates of endpoint variability generally reflected the results of the error rate analysis. These results do not support the discrete correction model of Fitts' Law proposed by Keele (1968).
The purpose of this study was to determine how subjects learn to adjust the characteristics of their manual aiming movements in order to make optimal use of the visual information and reduce movement error. Subjects practised aiming (120 trials) with visual information available for either 400 msec or 600 msec. Following acquisition, they were transferred to conditions in which visual information was available for either more or less time. Over acquisition, subjects appeared to reduce target-aiming error by moving to the target area more quickly in order to make greater use of vision when in the vicinity of the target. With practice, there was also a reduction in the number of modifications in the movement. After transfer, both performance and kinematic data indicated that the time for which visual information was available was a more important predictor of aiming error than the similarity between training and transfer conditions. These findings are not consistent with a strong "specificity of learning" position. They also suggest that, if some sort of general representation or motor programme develops with practice, that representation includes rules or procedures for the utilization of visual feedback to allow for the on-line adjustment of the goal-directed movement.
Participants (N = 16) were given extensive practice (1,500 trials) on a perceptual-motor aiming task. The full-vision (FV) group practiced with vision of their response cursor, whereas the no-vision (NV) group practiced in a condition without vision. Movements were made as quickly and accurately as possible, and knowledge of results (KR) was provided. The authors tested the importance of vision early and late in practice by transferring participants to the NV condition without KR. The effects of practice differed between the two conditions. The FV group increased the speed of initial impulse to get to the target quickly, then relied on vision to make discrete error corrections. Transfer tests revealed that reliance on vision remained after extensive practice. For the NV group, practice effects were associated with a reduction in the extent to which discrete error corrections were produced.
The focus of the present study was on determining whether the high level of directional accuracy found in aiming studies in which the subjects can see their hand in the visual periphery supports the existence of a kinetic visual channel or, rather, the advantage of binocular over monocular vision for movement directional control. The limits of this kinetic visual channel were also explored. The results of the 1st experiment indicated that seeing one's hand in the visual periphery is sufficient to ensure optimal directional aiming accuracy. Further, no differences in aiming accuracy were noted between monocular and binocular vision. These results supported the existence of a visual kinetic channel. In the 2nd experiment, whether this kinetic visual channel would operate with movements slower (55 degrees /s) than those usually used in studies that had proved its existence (over 110 degrees /s) was delineated. The results indicated that this visual kinetic channel was operative even at relatively slow movement velocities. Central vision of the hand seemed to be used for on-line directional control of relatively slow movements.
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