[Show abstract][Hide abstract] ABSTRACT: The ability to decide which of the two stimuli is presented first can be probed using a temporal order judgment (TOJ) task. When the stimuli are delivered to the fingers, TOJ decisions can be confounded by the fact that the hands can be moved to different locations in space. How and where this confounded information is processed in the brain is poorly understood. In the present set of experiments, we addressed this knowledge gap by using single-pulse transcranial magnetic stimulation (TMS) to disrupt processing in the right or left posterior parietal cortex (PPC) during a vibrotactile TOJ task with stimuli applied to the right and left index fingers. In the first experiment, participants held their hands in an uncrossed configuration, and we found that when the index finger contralateral to the site of TMS was stimulated first, there was a significant increase in TOJ errors. This increase did not occur when stimuli were delivered to the ipsilateral finger first. In the second experiment, participants held their hands in a crossed configuration and the pattern of errors was reversed relative to the first experiment. In both the first two experiments, significant increases in TOJ error were present with TMS over either hemisphere, regardless of arm configuration; however, they were larger overall following TMS over the right PPC. Control experiments using sham TMS indicated the systematic modulation in error was not due to nonspecific effects of the stimulation. Additionally, we showed that these TMS-induced changes in TOJ errors were not due to a reduced ability to detect the timing of the vibrotactile stimuli. Taken together, these results demonstrate that both the right and left PPC contribute to the processing underlying vibrotactile TOJs by integrating vibrotactile information and proprioceptive information related to arm position in space.
Experimental Brain Research 06/2014; 232(6):1689-98. · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract A multitude of events bombard our sensory systems at every moment of our lives. Thus, it is important for the sensory cortex to gate unimportant events. Tactile suppression is a well-known phenomenon defined as a reduced ability to detect tactile events on the skin before and during movement. Previous experiments found detection rates decrease just prior to and during finger abduction, and decrease according to the proximity of the moving effector. This study examined how tactile detection changes during a reach to grasp. Fourteen human participants used their right hand to reach and grasp a cylinder. Tactors were attached to the index finger, the fifth digit, and the forearm of both the right and left arm and vibrated at various epochs relative to a "go" tone. Results showed that detection rates at the forearm decreased before movement onset; whereas at the right index finger, right fifth digit and at the left index finger, left fifth digit, and forearm sites did not decrease like in the right forearm. These results indicate that the task affects gating dynamics in a temporally- and contextually dependent manner and implies that feed-forward motor planning processes can modify sensory signals.
[Show abstract][Hide abstract] ABSTRACT: Concussion frequently results in executive function deficits that can be specifically probed using task-switching tasks. The current study examined in detail the influence of concussion on task switching performance using both spatial and numerical stimuli. Individuals with concussion (n = 16) were tested within 48 hours of injury and 7, 14, and 28 days later. Healthy sex-, age-, height-, weight- and activity-matched controls (n = 16) were also tested at the same intervals. Switch costs were significantly greater in the participants with concussion than in the controls for both types of stimuli. By contrast, the global costs on non-switching trials were unaffected by concussion. We conclude that concussion has pronounced negative effects on the ability to switch task sets that generalize across task combinations (spatial or numerical) and that persist across at least a month after injury.
PLoS ONE 01/2014; 9(3):e91379. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: When the target of a goal-directed reach changes location, people normally respond rapidly and automatically to the target shift. Here, we investigate whether explicit knowledge about a moving target (knowing whether a location change is likely/unlikely) improves responsiveness, with the goal of understanding top-down effects on real-time reaching. In Experiment 1, we presented participants with pre-cues that indicated a 20 or 80 % likelihood of a target perturbation on that trial. When participants made pro-pointing responses to the target perturbations, their online response occurred later for 20 % trials than for 80 % trials, but this effect may have been due to suppression of the online response on 20 % trials, rather than enhancement of the response on 80 % trials. In Experiment 2, we presented participants with 50 and 100 % likelihood pre-cues, and observed no shortening of the latency on 100 % trials compared to 50 % trials, which suggests that expectation does not enhance the automatic response to a perturbation. However, we did observe more vigorous responses to the perturbation on the 100 % trials, and this contributed to shorter movement times relative to the 50 % trials. We also examined, in Experiment 2, whether prior knowledge about the direction of the target perturbation would shorten the latency of the online response, but we did not observe any reduction in latency. In sum, the onset of the automatic response appears to be suppressible, but not augmentable by top-down input. The possibility that the forcefulness of the automatic response is modifiable by expectation is examined, but not resolved.
Experimental Brain Research 01/2013; · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Head trauma in adolescents has been linked with deficits in attention and executive function that can compromise the performance of everyday tasks. Although previous research has examined this issue using computerized neuropsychological testing, little work has been done using laboratory-based measurements of attention and executive function in this population. A longitudinal analysis of recovery patterns of these measures among adolescents is central to understanding the effects of concussions across the age spectrum. PURPOSE: This study prospectively and longitudinally examined laboratory-based measures of attention and executive function in concussed adolescents sequentially over a 2-month period following injury. METHODS: Two measures of attention and executive function: the Attentional Network Test (ANT) and Task-Switching Test (TST) were administered to 20 concussed adolescents within 72 hours post injury as well as at one week, two weeks, one month, and two months post injury. Twenty healthy, matched control subjects were similarly assessed at the same time intervals. Data were analyzed by two-way, mixed effects analyses of variance to determine the effect of group and time on the dependent variables. RESULTS: Compared with control subjects, the concussed group exhibited a significantly greater switch cost on the TST (p = .038, mean difference value = 38 ms) and a significantly greater reaction time for the ANT conflict effect component (p = .015, mean difference value = 34 ms) for up to two months after injury. CONCLUSIONS: Concussed adolescents have difficulty recovering executive function after injury and may require extended recuperation time before full recovery is achieved. Evaluations focusing on attention and executive function can be useful additions in the assessment and follow-up after head injury.
Medicine and science in sports and exercise 12/2012; · 4.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The question of how infants attain upright sitting is at the core of understanding the development of most functional abilities. Our simple, practical method of securing the hips and different trunk segments while evaluating the infant's ability to vertically align and stabilize the trunk in space contributes a useful method and new insights into the development of upright control. Previous studies have considered the trunk to develop as a single segment. The goal of the present study was to examine how postural control changes across multiple trunk segments during typical development (TD) of sitting balance. For this purpose, electromyography (EMG) and kinematic data were collected at four levels of trunk support (axillae, midribs, waist, hips), in a longitudinal study of eight TD infants (3-9 mo of age). We found that developmental changes in stability were specific to the region of the trunk being investigated, changes in antagonistic muscle activity differed for the anterior-posterior versus the medial-lateral axis, and the relationship between muscle activation and movement changed from erratic attempts to gain upright position to anticipatory graded responses as infants developed upright control through a four-stage behavioral process. This information can be used by researchers to further refine hypotheses regarding this developmental process and by clinicians who wish to develop and test more specific treatment programs for children with postural dysfunction.
Journal of Neurophysiology 07/2012; 108(8):2215-29. · 3.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study was undertaken to determine if target predictability could modulate saccadic planning and timing at the level of the frontal eye fields (FEF). To this end, healthy participants performed two gap saccade tasks in which the targets were displaced left or right of the midline in either a predictable or a random fashion. Additionally, half of the participants were informed about this manipulation. Single pulse transcranial magnetic stimulation (TMS) was applied to the left FEF before, during, or after the target onset. We examined both the saccade latency and the frequency of multiple saccades (MS) (i.e., saccades that covered <90 % of the distance to the target and were subsequently followed by a corrective saccade). Findings revealed that saccadic reaction times were quickest to the more predictable target side and also confirmed that MS were released more quickly than single saccades. Further, the frequency of MS differed between target locations; higher frequencies of MS were found on the unpredictable side, showing more vulnerability to TMS disruption. In conclusion, we have demonstrated that target predictability modulates saccade planning and that this modulation takes place at least in part in the FEF. The influence of FEF in these processes is observed both in the latencies with which saccades are executed and in the timing and characteristics of the multiple saccades that are observed under different task constraints. Finally, the timing of the FEF contribution also appears to be influenced by the manipulation of target predictability. Each of these observations serves to further clarify the role of the human FEF in saccade planning.
Experimental Brain Research 06/2012; 221(1):51-8. · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to investigate the typical development of postural control in younger (5-6 yrs) and older (7-16 yrs) children (YTD and OTD) during two gait tasks, including level walking and obstacle-crossing, using a dual-task paradigm, and to compare the results of the children's performance with that of healthy young adults (HYA). Our findings revealed that gait control in typical children requires attentional resources to maintain stability. Moreover, dual-task interference was less in HYA compared to YTD and OTD. Gait performance decrements in the dual-task context were greater in YTD compared to OTD, whereas cognitive performance decrements in YTD and OTD were similar. In addition, dual-tasking affected cognitive performance more in YTD when gait task difficulty was increased. Results suggest a developmental trend in attentional resources used to control gait in typical children. Postural control during gait under dual-task conditions was improved when children were more mature, as attentional resources increased with age.
[Show abstract][Hide abstract] ABSTRACT: Accurate motor execution is achieved by estimating future sensory states via a forward model of limb dynamics. In the current experiment, we probed the time course over which state estimation evolves during movement planning by combining a bimanual arm crossing movement with a temporal order judgment (TOJ) task. Human participants judged which of two successive vibrotactile stimuli delivered to each index finger arrived first as they were preparing to either cross or uncross their hands. TOJ error rate was found to systematically vary in a time- and direction-dependent manner. When planning to cross the hands, error rate systematically increased as the vibrotactile stimuli were delivered closer in time to the onset of the movement. By contrast, planning to uncross the hands led to a gradual reduction in error rate as movement planning progressed. In both cases, these changes occurred before the actual alteration in hand configuration. We suggest that these systematic changes in error represent an interaction between the evolving state estimation processes and decisions regarding the timing of successive events.
Journal of Neuroscience 07/2011; 31(27):10019-22. · 6.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to examine how individuals modulate attention in a gait/cognition dual task during a 4-week period following a concussion. Ten individuals suffering from a grade 2 concussion and 10 matched controls performed a single task of level walking, a seated auditory Stroop task and a simultaneous auditory Stroop and walking task. Reaction time and accuracy were measured from the Stroop task. Dynamic balance control during gait was measured by the interaction (displacement and velocity) between the center of mass (CoM) and center of pressure (CoP) in the coronal and sagittal planes. Concussed individuals shifted from conservative control of balance (shorter separation between CoM and CoP) immediately after injury to normal balance control over 28 days post-injury. Immediately after injury, correlations analyses using each subject on each testing day as a data point showed that there was a spectrum of deficient performance among concussed individuals on the first testing day. Within a testing session, deficiencies in reaction time of processing involved in the Stroop task were commonly seen with reduce dynamic balance control. However, the prioritization was not always towards the same task between trials. There were no correlations in the control group. Information provided in this study would enhance our understanding of the interaction between attention and gait following concussion.
Journal of NeuroEngineering and Rehabilitation 01/2011; 8:8. · 2.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The supplementary motor area (SMA) is involved in planning limb movements. An important component of such planning is the prediction of the sensory consequences of action. The authors used transcranial magnetic stimulation (TMS) to probe the contribution of SMA to motor planning during a predictive load-bearing task. Single TMS pulses were delivered over the SMA after a cue instructing the participant to release a platform supporting his or her right hand, which in turn held a 2 kg mass. Participants were less able to bear the load successfully when TMS was delivered 400-500 ms prior to the response. This result suggests that the SMA contributes to the prediction of the sensory consequences of movement well before movement onset.
Journal of Motor Behavior 01/2011; 43(4):303-9. · 1.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Deficits in postural control are one of the hallmarks of disability in children with cerebral palsy (CP). Yet, much remains unknown regarding the etiology of postural deficits in these children. Here we evaluated postural control at a simplified task level by measuring head stability during quiet sitting while systematically manipulating the level of trunk support and vision in 15 children with CP (6-16 years), 26 typically developing (TD) children (4-14 years), and 11 adults. While TD children did not differ significantly from adults, children with CP had greater head movement than adults in both the sagittal and frontal planes under all conditions except frontal plane movement with Torso Support. Vision did not affect head stability in the sagittal plane for any group while it had differential effects on head stability in the frontal plane. Lack of vision improved head stability in adults and older TD children while destabilizing the head in young children (TD and CP) during the most unstable sitting position. Moreover, vision affected children with CP differently depending on their movement disorder. Children with spastic CP performed worse with eyes closed while those with dyskinetic CP had improved head stability with eyes closed. Our results demonstrate that children with mild to moderate CP have deficits in head stability even during quiet sitting.
Experimental Brain Research 09/2009; 201(1):13-23. · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To compare the effect of 3 different approaches to balance training on dual-task balance performance in older adults with balance impairment.
A double-blind, randomized controlled trial.
University research laboratory.
Older adults (N=23) with balance impairment (mean age, 74.8y). They scored 52 or less on the Berg Balance Scale (BBS) and/or walked with a self-selected gait speed of 1.1m/s or less.
Participants were randomly assigned to 1 of 3 interventions: single-task training, dual-task training with fixed-priority instructions, and dual-task training with variable-priority instructions. Participants received 45-minute individualized training sessions, 3 times a week for 4 weeks.
Gait speed under single-task and dual-task conditions was obtained at baseline, the second week, the end of training, and the twelfth week after the end of training. Other measures, including the BBS and the Activities-specific Balance Confidence (ABC) Scale, were collected at baseline and after training.
Participants in all groups improved on the BBS (P<.001; effect size [ES]=.72), and walked significantly faster after training (P=.02; ES=.27). When a cognitive task was added, however, only participants who received dual-task training with fixed-priority instructions and dual-task training with variable-priority instructions exhibited significant improvements in gait speed (P<.001, ES=.57; and P<.001, ES=.46, respectively). In addition, only the dual-task training with variable-priority instructions group demonstrated a dual-task training effect at the second week of training and maintained the training effect at the 12-week follow-up. Only the single-task training group showed a significant increase on the ABC after training (P<.001; ES=.61).
Dual-task training is effective in improving gait speed under dual-task conditions in elderly participants with balance impairment. Training balance under single-task conditions may not generalize to balance control during dual-task contexts. Explicit instruction regarding attentional focus is an important factor contributing to the rate of learning and the retention of the dual-task training effect.
Archives of physical medicine and rehabilitation 03/2009; 90(3):381-7. · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to longitudinally compare the sensitivity of previously documented paradigms for measuring balance control during gait following a concussion. We hypothesized that gait with a concurrent cognitive task would be most sensitive to the effects of concussion on dynamic balance control. Individuals with concussion (n = 30) and matched controls (n = 30) performed a single task of level walking, attention divided walking, and an obstacle-crossing task at two heights. Testing occurred four times post-injury. Balance control during gait was assessed with whole-body center of mass and center of pressure motion. The single-task level walking task did not result in any significant differences in balance control between individuals with concussion and control subjects. Within 48 hours post-injury, individuals with concussion walked slower and allowed less motion of their center of mass in the sagittal plane when attention was divided during walking, but there were no group differences by day 6 for this task. Group differences in balance control during obstacle crossing was unremarkable during the first two testing sessions, but by day 14 individuals with concussion displayed less mediolateral motion of their center of mass. Attention divided gait is able to better distinguish gait adaptations immediately following a concussion, but obstacle crossing can be used further along in the recovery process to detect new gait adaptations.
Journal of NeuroEngineering and Rehabilitation 02/2009; 6:25. · 2.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to compare the efficiency of three different balance training strategies in an effort to understand the mechanisms underlying training-related changes in dual-task balance performance of older adults with balance impairment. Elderly individuals with balance impairment, age 65 and older, were randomly assigned to one of three individualized training programs: single-task (ST) balance training; dual-task training with fixed-priority (FP) instruction; and dual-task training with variable-priority (VP) instruction. Balance control during gait, under practiced and novel conditions, was assessed by calculating the center of mass and ankle joint center inclination angles in the frontal plane. A smaller angle indicated better balance performance. Other outcomes included gait velocity, stride length, verbal reaction time, and rate of response. All measures were collected at baseline and the end of the 4-week training. Results indicated that all training strategies were equally effective (P>.05) at improving balance performance (smaller inclination angle) under single-task contexts. However, the VP training strategy was more effective (P=.04) in improving both balance and cognitive performance under dual-task conditions than either the ST or the FP training strategies. Improved dual-task processing skills did not transfer to a novel dual-task condition. Results support Kramer et al.'s proposal that VP training improves both single-task automatization and the development of task-coordination skills.
[Show abstract][Hide abstract] ABSTRACT: Recent research has explored dual-task deficits during locomotion in older adults, yet the mechanisms underlying these deficits are poorly understood. In the current study, we examined one possible factor contributing to these deficits, the inability to flexibly allocate attention between two tasks.
Twelve healthy young adults and 12 healthy elderly adults performed obstacle avoidance while walking and an auditory Stroop task either alone or simultaneously.
Using an attentional allocation index (AAI) to compare performance of healthy young and older adults and to measure the flexibility of allocation of attention, results showed a tendency in older adults toward a decreased ability to flexibly allocate their attention between the two tasks, with small AAI values. The decreased ability to allocate attention in older adults was found to be more prominent in the auditory Stroop task performance than in the obstacle avoidance task.
This study suggests that an important factor contributing to decreased dual-task performance in older adults when simultaneously performing a postural and secondary cognitive task is a reduced ability to flexibly allocate attention between the two tasks, with the general ability to switch attention flexibly being predictive of the ability to adhere to a prioritized focus.
The Journals of Gerontology Series A Biological Sciences and Medical Sciences 01/2009; 63(12):1364-9. · 4.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Saccadic eye movements are used to rapidly align the fovea with the image of objects of interest in peripheral vision. We have recently shown that in children there is a high preponderance of quick latency but poorly planned saccades that consistently fall short of the target goal. The characteristics of these multiple saccades are consistent with a lack of proper inhibitory control of cortical oculomotor areas on the brainstem saccade generation circuitry.
In the present paper, we directly tested this assumption by using single pulse transcranial magnetic stimulation (TMS) to transiently disrupt neuronal activity in the frontal eye fields (FEF) and supplementary eye fields (SEF) in adults performing a gap saccade task. The results showed that the incidence of multiple saccades was increased for ispiversive but not contraversive directions for the right and left FEF, the left SEF, but not for the right SEF. Moreover, this disruption was most substantial during the approximately 50 ms period around the appearance of the peripheral target. A control condition in which the dorsal motor cortex was stimulated demonstrated that this was not due to any non-specific effects of the TMS influencing the spatial distribution of attention.
Taken together, the results are consistent with a direction-dependent role of the FEF and left SEF in delaying the release of saccadic eye movements until they have been fully planned.
PLoS ONE 01/2009; 4(9):e7278. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Re-injury to the brain during recovery from an initial concussion leads to increased probability of permanent brain damage or death. Recovery from concussion has been proposed to be ongoing even up to a month post-injury. The goal of the current study was to investigate the relationship between the visuospatial orientation of attention and obstacle avoidance during gait in individuals that have recently suffered a concussion (mTBI) over a month post-injury. MTBI subjects and matched control subjects performed the attentional network test (ANT), designed to isolate several different components of attention. Obstacle crossing during gait with and without a concurrent attention dividing task was also performed. Reaction times from the ANT and obstacle clearance measurements were the main dependent variables. We observed that concussed individuals had statistically more obstacle contacts than controls. The ability to orient attention in space was also statistically deficient immediately after a concussion, and this was correlated with lower obstacle clearances of the leading foot. Similar correlations could also be found between both leading and trailing foot avoidance and spatial orientation of attention in participants with concussion when attention was divided during obstacle crossing, and these relationships gradually weakened as recovery progressed. By contrast, spatial attention and obstacle clearance were not significantly correlated in control subjects. These findings indicate that patients with mTBI who display greater spatial attention deficits cross over the obstacle with a lower clearance than patients with less or without spatial attention deficits, leading to an increased probability of obstacle contact.
Experimental Brain Research 01/2009; 194(1):67-77. · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent research has begun to explore the ability of older adults to perform balance tasks while simultaneously performing a secondary cognitive task; however, it has suffered from limitations regarding the mechanisms underlying the problems that cause dual-task deficits in older adults with balance impairments. Two possible attentional mechanisms (reduced general attentional capacity vs. a true dual-task performance deficit and inability to allocate attention between two tasks) contributing to balance constraints were examined.
Twelve healthy elderly adults and 12 elderly adults with balance impairments (BIOA) were asked to perform obstacle avoidance while walking, either alone or simultaneously with an auditory Stroop task. Two experiments were designed to examine attentional mechanisms that may contribute to reduce performance in the dual-task situations for the BIOA.
Experiment 1 determined whether for BIOA, single vs. dual-task performance conditions led to similar effects as a single-task difficulty (congruent vs. incongruent) manipulation. Results indicated that dual-task performance reduction did not exceed that of the difficult single task, suggesting that neither older adult group showed a true dual-task performance deficit, but rather BIOA showed a reduced attentional capacity. Experiment 2 showed that BIOA also showed deficits in flexibly focusing their attention between two tasks according to instructions.
Our study confirmed that the ability to allocate attention between a postural task and a secondary cognitive task was impaired in BIOA; it is suggested that inability to flexibly allocate attention could be one important factor among many factors that contribute to balance constraints during gait in fallers.
Brain research 12/2008; 1248:59-67. · 2.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reaching to grasp an object of interest requires complex sensorimotor coordination involving eye, head, hand and trunk. While numerous studies have demonstrated deficits in each of these systems individually, little is known about how children with cerebral palsy (CP) coordinate multiple motor systems for functional tasks. Here we used kinematics, remote eye tracking and a trunk support device to examine the functional coupling of the eye, head and hand and the extent to which it was constrained by trunk postural control in 10 children with CP (6-16 years). Eye movements in children with CP were similar to typically developing (TD) peers, while hand movements were significantly slower. Postural support influenced initiation of hand movements in the youngest children (TD & CP) and execution of hand movements in children with CP differentially depending on diagnosis. Across all diagnostic categories, the most robust distinction between TD children and children with CP was in their ability to isolate eye, head and hand movements. Results of this study suggest that deficits in motor coordination for accurate reaching in children with CP may reflect coupled eye, head, and hand movements. We have previously suggested that coupled activation of effectors may be the default output for the CNS during early development.
Experimental Brain Research 10/2008; 192(2):155-65. · 2.22 Impact Factor