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Li-Shan Chou

Publications and source records attributed to Li-Shan Chou.

17 recordsLinked to original sources
PubMed2006

Cancelling planned actions following mild traumatic brain injury.

Mild traumatic brain injury (mTBI) leads to a variety of attentional, cognitive, and sensorimotor deficits. An important aspect of behavior that intersects each of these functions is the ability to cancel a planned action. Thus, the purpose of this study was to determine the effects of mTBI on the ability to perform a countermanding saccade task. In this task, participants were asked to generate a saccade to a target appearing in peripheral vision, but to inhibit saccade execution if an auditory stop signal was presented. The delay between the appearance of the peripheral target and the presentation of the auditory stop signal was varied between 0 and 125ms. We found that the change in the probability of cancelling the saccade as a function of this delay was no different between participants with mTBI tested within 2 days of their injury and matched controls. However, saccadic reaction times and the stop signal reaction time were unexpectedly faster in the participants with mTBI and, furthermore, they inaccurately inhibited saccades during 15% of the trials with no stop signal. Taken together, this data suggests that the ability to cancel planned actions is subtly yet adversely affected by mTBI.

Adult↗
PubMed2006

Cognitive task effects on gait stability following concussion.

The purpose of this study was to determine how two different types of concurrent tasks affect gait stability in patients with concussion and how balance is maintained. Fourteen individuals suffering from a grade II concussion and 14 matched controls performed a single task of level walking and two types of concurrent tasks during level walking: a discrete reaction time task and a continuous sequential question and answer task. Common gait spatial/temporal measurements, whole-body center of mass motion, and the center of pressure trajectory were recorded. Concussed individuals demonstrated differences in gait while performing single-task level walking and while being challenged with a more difficult secondary task compared to normal controls. Concussed individuals adopted a slower, more conservative gait strategy to maintain stability, but still exhibited signs of instability with center of mass deviations in the coronal plane increasing by 13% during the question and answer dual-task and 26% more than control subjects. Trends of attentional deficits were present with the question and answer task, while the reaction time task seemed to help concussed individuals be more alert to their gait and stability. Recommendations for a sensitive testing protocol of deficits following concussion are explained.

Adult↗
PubMed2006

Altered balance control following concussion is better detected with an attention test during gait.

The purpose of this study was to examine the effects of concussion on gait stability when either a cognitive or motor perturbation is imposed. Fourteen individuals suffering from a grade II concussion and 14 matched controls performed a single task of level walking, a continuous sequential question and answer task while walking, and an obstacle-crossing task. Common gait spatial/temporal measurements, whole-body center of mass motion, and center of pressure trajectory were assessed. Concussed individuals adopted a more conservative strategy to maintain gait stability. Some measurements indicating conservative gait were seen during obstacle crossing, but this was most evident during the Q&A task. Concussed individuals also displayed signs of possible instability during the Q&A task. The question and answer task was most sensitive to distinguishing concussed individuals from healthy individuals, supporting the use of a similar dual-task modality in future testing after concussion to determine a proper time for return to activity.

Adult↗
PubMed2006

The influence of mild traumatic brain injury on the temporal distribution of attention.

The purpose of this study was to examine whether the temporal dynamics of attention was deficient in participants who have recently experienced mild traumatic brain injury (mTBI). For this purpose the rapid serial visual presentation (RSVP) task was used and the performance of participants with mTBI was compared to that of controls matched for age, gender, education, and activity type. In the RSVP task a stream of rapidly presented letters is displayed with target and probe letters separated by varying durations. The participant is required to identify the target letter and determine whether the probe letter was present or not. Previous research has shown that healthy participants display an attentional blink: they fail to detect the probe letter when it appears within approximately 500 ms of the target letter. We found that participants with mTBI had a normal attentional blink-it was neither greater in magnitude nor longer in duration than that displayed by the control participants. However, the participants with mTBI did show evidence of attentional competition-making more errors in identifying the target letter when the probe letter was presented-that was not present in the control participants. Taken together, these results suggest that the temporal constraints of attention are subtly but systematically affected by mTBI.

Adolescent↗
PubMed2006

Detection of gait instability using the center of mass and center of pressure inclination angles.

OBJECTIVE: To define a parameter that quantifies balance control during gait and better identifies elderly people who are at a higher risk of falling. DESIGN: Controlled study. SETTING: University research laboratory. PARTICIPANTS: Twelve elderly patients (mean age, 76.9+/-6y) with complaints of imbalance during walking, or with a history of falls, and 12 matched healthy elderly adults. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Temporal-distance gait parameters (gait velocity, stride length, step width); and sagittal and frontal center of mass (COM) and center of pressure (COP) inclination angles. RESULTS: Elderly patients demonstrated a significantly greater medial, but a significantly smaller anterior, inclination angle than their matched controls during both unobstructed and obstructed gait. The medial COM-COP inclination angle was not affected by the gait velocity in the healthy elderly. When the 2 groups were compared at a similar gait velocity ( approximately 1m/s), the elderly patients still had a significantly greater medial COM-COP inclination angle than did the controls. CONCLUSIONS: Instantaneous COM-COP inclination angles during walking provide information about the ability to control COM position in relation to the corresponding COP. The medial COM-COP inclination angle may be a sensitive measure of gait stability in the elderly.

Accidental Falls↗
PubMed2006

Gait stability following concussion.

INTRODUCTION: The need to identify functional impairment following a brain injury is critical to prevent reinjury during the period of recovery. However, little is known about the effect of concussion on dynamic motor function. PURPOSE: The purpose of this study was to examine the effect of concussion on a dynamic motor task under conditions of divided and undivided attention over the course of 28 d. METHODS: Fifteen subjects with concussions (CONC) and 15 uninjured controls (NORM) were observed while walking with undivided attention and while concurrently completing simple mental tasks. The CONC were assessed within 48 h of injury and again at 5, 14, and 28 d postinjury. The NORM were evaluated at the same time intervals. Whole-body motion data were collected to examine displacement and velocity of the center of mass (COM) and the maximum separation between the COM and center of pressure (COP). Three-way repeated-measures mixed-design ANOVA and Tukey post hoc tests were completed to determine differences between group, task, and testing day (P<0.05). RESULTS: Several aspects of gait stability were compromised in the CONC group for up to 4 wk after injury. CONC were found to walk significantly slower during dual tasks on all testing days when compared with the uninjured controls. The injured subjects were also found to have greater sway and sway velocity than controls when attention was divided for up to 28 d postinjury. CONCLUSION: The findings of this study suggest that concussion may have long-term observable and measurable effects on the control of gait stability.

Adult↗
PubMed2005

Tracking the recovery of visuospatial attention deficits in mild traumatic brain injury.

The goal of the current investigation was to probe the deficits in the alerting, orienting and executive components of visuospatial attention in individuals who have recently suffered a mild traumatic brain injury (mTBI) and to assess the rate and degree of recovery for each of these components over a month post-injury. A group design was employed to assess and compare the performance of participants (12 males, 8 females; mean age: 21 +/- 1.74 years) identified with mTBI relative to control subjects matched for gender, age, height, weight and activity level. Participants performed the attentional network test, designed to isolate the constituents of attention into alerting, orienting and executive components. Reaction times (RTs) and response accuracy were the main dependent variables. The results showed that the orienting and executive components were significantly affected by mTBI immediately after the injury, whereas the alerting component was not. Furthermore, participants with mTBI recovered from the deficits in the orienting component of attention within a week of their injury, whereas the deficits in the executive component remained throughout the month post-injury. In addition, the RT cost to generate accurate compared with inaccurate responses was significantly larger in participants with mTBI than in controls, and this difference was maintained throughout the 1 month testing period. These findings indicate that the regions of the brain associated with the orienting and executive components of visuospatial attention may be most susceptible to neural damage resulting from mTBI. Moreover, the lack of recovery in the executive component indicates that the degree and time course for recovery may be regionally specific.

Adolescent↗
PubMed2005

Comparison of subjective and objective measurements of balance disorders following traumatic brain injury.

Patients with mild traumatic brain injury (TBI) often complain of dizziness. However, these problems may be undetected by a clinical exam. Therefore, the purpose of this study was to evaluate the relationships between the subjective and objective measures of balance impairment. Ten patients with TBI (6 men and 4 women) and 10 matched controls participated in this study. Average duration since the TBI was 2.8 years (range 0.4-14.4). Six of the 10 subjects with TBI had abnormal imaging studies. All subjects and controls had a normal neuromuscular exam. Tinetti Balance Assessments were obtained and the TBI group was not significantly different from the control group. The Dizziness Handicap Inventory (DHI) score supported their complaints of "unsteadiness" and "imbalance" from the subjects with TBI. The DHI score was 32 +/- 23 (range 4-68) out of a maximum possible score of 100. Balance was tested using computerized dynamic posturography. The Sensory Organization Test score was significantly lower for subjects who had a TBI (70 +/- 12) compared to the control subjects (80 +/- 8), which indicated that the subjects with TBI had poorer balance than the control subjects. A 13-link biomechanical model of the human body was used to compute the kinematics of the whole body center of mass (COM) while walking on a level surface. The subjects with TBI had significantly less displacement in the anterior/posterior direction, walked significantly slower, had significantly greater medial/lateral sway and velocity than the normal controls, and had significantly greater medial/lateral imbalance. There was a significant relationship between the physical aspects of the DHI and posturography. There was also significant relationship between the physical, functional, and total DHI and the motion of the COM. Overall, the motion of the COM predicted between 42 and 69% of the DHI score. The present study has demonstrated that objective measurements can quantify the patient's functional deficits. Therefore, these objective measurement techniques should be used to assess the clinical complaints of imbalance from patients with TBI.

Adult↗
PubMed2005

The effect of divided attention on gait stability following concussion.

BACKGROUND: The need to identify functional impairment following a brain injury is critical to prevent re-injury during the period of recovery. While many neuropsychological tests have been developed to assess cognitive performance, relatively little information on gait and dynamic stability is available on motor task performance for young adults following concussion. This study was performed to investigate the effect of divided attention following concussion on various gait variables. It was hypothesized that, when compared to uninjured controls, concussed subjects would demonstrate deficits in maintenance of dynamic stability. METHODS: Ten subjects with Grade 2 concussion completed testing within 48 h of injury as well as 10 age-, height-, weight-, and activity-matched controls. The gait protocol consisted of level walking under two conditions: (1) undivided attention (single-task) and (2) while simultaneously completing simple mental tasks (dual-task). Whole-body motion data were collected using a six-camera motion analysis system. A 13-segment biomechanical model was used to compute whole body center of mass motion and velocity. FINDINGS: Walking with a concurrent cognitive task resulted in significant changes in gait and center of mass measurements for both groups. Concussed subjects were found to be able to conservatively adjust their whole body center of mass motion to maintain dynamic stability while walking without divided attention. However, while walking with divided attention, subjects with concussion demonstrated a significantly greater medio-lateral center of mass sway. INTERPRETATION: These data suggest that the ability to control and maintain stability in the frontal plane during walking is diminished under divided attention in individuals following a concussion.

Adult↗
PubMed2005

Increased muscular challenge in older adults during obstructed gait.

Skeletal muscle strength is known to decline with age. Although lower extremity (LE) muscle strength is critical to maintaining dynamic stability, few studies have investigated lower extremity muscle challenge during activities of daily living. The purpose of this study was to investigate the effects of age and obstructed gait on relative lower extremity muscular challenge, with respect to available joint strength. Fifteen healthy young and fifteen healthy older adults were asked to walk over level ground and step over obstacles. Pre-amplified surface electrodes were used to measure bilateral muscular activation of the gluteus medius (GM), vastus lateralis (VL), and gastrocnemius (GA). Muscle activation signals were normalized to peak magnitudes collected during maximal manual muscle testing (MMT). Normalized magnitudes were analyzed during the double-support phase for gluteus medius and vastus lateralis and during the single-support phase for gastrocnemius. A two-factor ANOVA was used to test for age group effect, with repeated measure of obstacle height. In general, older adults demonstrated greater relative activation levels compared to young adults. Gluteus medius activity was significantly greater in the elderly as compared to young during periods of double-support (weight transfer). Increased obstacle height resulted in greater relative activation in all muscles, confirming the increased challenge to the musculo-skeletal system. While healthy elderly adults were able to successfully negotiate obstacles of different heights during walking, their muscular strength capacity was significantly lower than young adults, resulting in relatively higher muscular demands. The resulting potential for muscular fatigue during locomotion may place individuals at higher risk for trips and/or falls.

Activities of Daily Living↗
PubMed2005

A model for detecting balance impairment and estimating falls risk in the elderly.

Traumatic falls are a prevalent and costly threat to elderly adults. Accurate risk assessment is necessary for reducing incidence of falls. The objective of this study was to test the feasibility of a balance impairment detection model using tasks of sample categorization and falls risk estimation. Model design included an artificial neural network and a statistical discrimination method. The first system produced an individual categorization value, which was then assessed in the second system for relative risk of falls, compared to a normative distribution of healthy elderly peers. Input data included leg muscle electromyographic amplitudes, temporal-distance measures of gait, and medio-lateral measures of whole body center of mass motion. These input data were compiled from a sample of healthy elderly adults (n = 19) and a sample with impaired balance (n = 10) to develop and test the model. Accuracy of sample categorization was assessed using a relative operating characteristic (ROC) value. For relative risk estimation, categorical delineation of risk level was adopted. Sample categorization results reached ROC values of 0.890. Relative risk was frequently assessed at high or very high risk for experiencing falls. Temporal-distance measures were most influential in categorization accuracy, producing the most consistent risk estimates. Combined inputs further improved model performance. This model shows potential for detecting balance impairment and estimating falls risk; thereby indicating need for referral for falls prevention intervention.

Accidental Falls↗
PubMed2005

Neural network estimation of balance control during locomotion.

Gait patterns of the elderly are often adjusted to accommodate for reduced function in the balance control system and a general reduction in skeletal muscle strength. Recent studies have demonstrated that measures related to motion of whole body center of mass (COM) can distinguish elderly individuals with balance impairment from healthy peers. Accurate COM estimation requires a multiple-segment anthropometric model, which may restrict its broad application in assessment of dynamic instability. Although temporal-distance measures and electromyography have been used in evaluation of overall gait function and determination of gait dysfunction, no studies have examined the use of gait measurements in predicting COM motion during gait. The purpose of this study was to demonstrate the effectiveness of an artificial neural network (ANN) model in mapping gait measurements onto COM motion in the frontal plane. Data from 40 subjects of varied age and balance impairment were entered into a 3-layer feed-forward model with back-propagated error correction. Bootstrap re-sampling was used to enhance the generalization accuracy of the model, using 20 re-sampling trials. The ANN model required minimal processing time (5 epochs, with 20 hidden units) and accurately mapped COM motion (R-values up to 0.89). As training proportion and number of hidden units increased, so did model accuracy. Overall, this model appears to be effective as a mapping tool for estimating balance control during locomotion. With easily obtained gait measures as input and a simple, computationally efficient architecture, the model may prove useful in clinical scenarios where electromyography equipment exists.

Age Factors↗
PubMed2004

Dynamic instability during obstacle crossing following traumatic brain injury.

Patients with traumatic brain injury (TBI) complain of "imbalance" or "unsteadiness" while walking, despite a normal gait on clinical examination. Thus, the purpose of this study was to determine if it was possible to quantitatively assess dynamic stability that did not have an obvious neuromuscular origin in individuals following TBI. Ten patients with documented TBI and 10 age, gender, and stature-matched healthy individuals participated in the study. All subjects were instructed to perform unobstructed level walking and to step over obstacles corresponding to 2.5%, 5%, 10%, and 15% of their height. A 13-link biomechanical model of the human body was used to compute the kinematics of the whole body center of mass (COM). Subjects with TBI walked with a significantly slower gait speed and shorter stride length than their matched controls. Furthermore, subjects with TBI displayed a significantly greater and faster medio-lateral (M-L) COM motion and maintained a significantly greater M-L separation distance between their COM and center of pressure (COP) than their matched control subjects. These measurements indicate that subjects with TBI have difficulty maintaining dynamic stability in the frontal plane and have a reduced ability to successfully arrest their sagittal momentum. These findings provide an objective measurement that reflects the complaints of instability not observable on clinical examination for individuals who have suffered a TBI. This ability to identify any functional impairment after a traumatic brain injury that may affect patient safety is critical for prevention of re-injury during the recovery period.

Biomechanical Phenomena↗
PubMed2004

Age-related reduction in sagittal plane center of mass motion during obstacle crossing.

Accidental falls are a leading cause of injury and death in the growing elderly population. Traumatic falls are frequent, costly, and debilitating. Control of balance during locomotion is critical for safe ambulation, but relatively little is known about the natural effect of aging on dynamic balance control. Samples of healthy young (n = 13) and elderly (n = 13) subjects were compared in the interactive measures of center of mass (COM) and center of pressure (COP) during level walking and obstacle crossing conditions. Obstacle heights were normalized to individual body height (2.5%, 5%, 10%, and 15%). Temporal-distance (T-D) variables of gait were also compared. Statistical analyses were conducted using a two-way ANOVA for subject group and obstacle height. T-D parameters were not significantly different between groups; nor were frontal plane COM and COP parameters. Significant age differences did exist for antero-posterior (A/P) motion of the COM (decreased motion in the elderly), and its relationship with the COP (reduced separation between the two variables in the elderly). Anterior COM velocities were also significantly lower in the elderly group. The results confirm the ability of healthy elderly adults to maintain dynamic balance control in the frontal plane during locomotion. Reduced A/P distances between the COM and COP indicate a conservative reduction of the mechanical load on joints of the supporting limb. This conservative strategy may be related to a reduction in muscle strength as it occurs in the natural aging process.

Accidental Falls↗
PubMed2003

Medio-lateral motion of the center of mass during obstacle crossing distinguishes elderly individuals with imbalance.

This study was performed to investigate whether elderly patients with imbalance can be distinguished from healthy elderly subjects by comparing their whole body center of mass (COM) motion in the medio-lateral (M-L) direction during obstacle crossing. Nine healthy elderly adults and six elderly patients having complaints of 'dizziness' or 'unsteadiness' during walking (three with bilateral/unilateral vestibular weakness and three with unclear diagnosis) were recruited to perform unobstructed level walking and crossing of obstacles set to 2.5, 5, 10 and 15% of each subject's height. Kinematics of the COM was calculated using a weighted sum average of a 13-segment biomechanical model. There were no significant group differences for the temporal-distance gait parameters during all testing conditions. However, elderly patients with balance disorders demonstrated significantly greater and faster lateral motion of the COM when crossing over obstacles. These measurements distinguish elderly patients with imbalance from healthy elderly subjects. Furthermore, the increased M-L motion of the COM during obstacle crossing showed a positive correlation with an increased M-L range of motion of the swing foot trajectory. This increase in M-L motion indicates a compensatory adjustment in the swing foot trajectory to land the swing foot at an appropriate location that would establish a new base of support to counter the balance disturbance in the frontal plane.

Aged↗
PubMed2003

An assessment of gait and balance deficits after traumatic brain injury.

OBJECTIVE: To assess the sensations of instability that many patients report after traumatic brain injury (TBI). DESIGN: A controlled study. SETTING: A motion analysis and vestibular and balance laboratory. PARTICIPANTS: Twenty subjects, 10 with TBI and complaints of instability, and 10 without TBI. INTERVENTIONS: Balance and gait analysis. MAIN OUTCOME MEASURES: Dizziness Handicap Inventory (DHI), caloric irrigation, optokinetic testing, Dix-Hallpike Test, posturography, and center of mass (COM) movement. RESULTS: Subjects were well matched in terms of age, height, weight, and gender. DHI scores of those with and without TBI differed significantly (32.2+/-23.0 vs 0.2+/-0.63, P<.001). Caloric and optokinetic circularvection testing were abnormal only in subjects with TBI (8/10 and 4/10, respectively). Benign paroxysmal positioning vertigo was present in only 3 subjects with TBI, and this either resolved spontaneously (n=1) or was successfully treated (n=2). Composite posturography scores of those with and without TBI differed significantly (69.6+/-35.8 vs 79.5+/-40.5, P=.02). Gait parameters also differed significantly between the groups (P=.05), with the subjects with TBI having lower anterior and posterior and higher medial and lateral COM displacements and velocities. CONCLUSIONS: Patients' complaints of instability after TBI may have objective correlates and may be rectifiable. Balance and gait testing in these patients is warranted.

Adolescent↗