Naznin Virji-Babul

Gesture-Based affective computing on motion capture data

This paper presents research using full body skeletal movements captured using video-based sensor technology developed by Vicon Motion Systems, to train a machine to identify different human emotions. The Vicon system uses a series of 6 cameras to capture lightweight markers placed on various points of the body in 3D space, and digitizes movement into x, y, and z displacement data. Gestural data from five subjects was collected depicting four emotions: sadness, joy, anger, and fear. Experimental results with different machine learning techniques show that automatic classification of this data ranges from 84% to 92% depending on how it is calculated. In order to put these automatic classification results into perspective a user study on the human perception of the same data was conducted with average classification accuracy of 93%.

Joint stiffness and gait pattern evaluation in children with Down syndrome

Hypotonia, ligament laxity and motor alterations are characteristic for patients with Down syndrome (DS). The purpose of this study was the evaluation of typical gait pattern of subjects with Down syndrome and the quantification of their joint stiffness, connected with ligament laxity and hypotonia, as a possible compensation. 98 children with DS (mean age: 11.7 years; range: 6-15 years) and 30 healthy children (control group (CG); mean age: 11 years; range: 5-13 years) underwent full 3D gait analysis at self-selected speed. Subjects with DS walked with more hip flexion during the whole gait cycle, knee flexion in stance phase, a limitation of the knee range of motion, and plantarflexion of the ankle at initial contact. Ankle power was limited as evident in terminal stance and pre-swing, represented by a low propulsive capacity at push-off, too. Hip joint stiffness was increased in general in patients with DS versus normal subjects while ankle joint stiffness revealed a lower value instead.

Stiffness and postural stability in adults with Down syndrome.

The purpose of this study was to characterize postural sway in quiet standing under eyes-open and eyes-closed conditions, and to obtain a measure of postural stiffness during quiet standing in adults with Down syndrome (DS) versus control subjects. We obtained descriptive measures from centre-of-pressure (COP) data and analysed and compared COP trajectories and postural stiffness estimates from two stochastic models, the “pinned polymer” (PP) and “inverted pendulum” (IP) models. These estimates were correlated with clinical measures of muscle tone. Our results showed that overall, estimated values for postural stiffness from both models were larger for the DS group than for normal controls. In addition, average stiffness measures were greater under the eyes-closed condition than under the eyes-open condition for the DS group. The IP model detected significant trends over trials whereas the PP model did not. Clinical assessment of muscle tone for the DS group ranged from low to high-normal and there was no significant correlation with the postural stiffness measures obtained from either model. These results suggest that individuals with DS have the ability to modulate their underlying “stiffness” under conditions of quiet standing. Furthermore, there appears to be no strong relationship between clinical measures of muscle tone and postural stiffness measures under dynamic conditions.

Diffusion Tensor Imaging of Sports-Related Concussion in Adolescents

Concussion is among the least understood neurologic injuries. The impact of concussion on the adolescent brain remains largely unknown. This study sought to establish short-term changes in white-matter integrity after sports-related concussion in adolescents, and examine the association between changes in white-matter integrity and a clinical measure of concussion. Twelve adolescents, aged 14-17 years with a sports-related concussion within 2 months, and 10 age-matched adolescents with no history of concussion were evaluated with the Sports Concussion Assessment Tool 2 and diffusion tensor imaging. Two measures compared the two groups: fractional anisotropy and mean diffusivity. Whole-brain fractional anisotropy values significantly increased (F(1,40) = 6.29, P = 0.010), and mean diffusivity values decreased (F(1,40) = 4.75, P = 0.036), in concussed athletes compared with control participants. Total scores on the Sports Concussion Assessment Tool 2 were associated with whole-brain fractional anisotropy. Mean diffusivity values with lower scores were associated with higher fractional anisotropy (R(2) = 0.25, P = 0.017) and lower mean diffusivity (R(2) = 0.20, P = 0.038). We provide evidence of structural changes in the integrity of white matter in adolescent athletes after sports-related concussion.

Influence of joint interactional effects on the coordination of planar two-joint arm movements

We have examined EMG-movement relations in two-joint planar arm movements to determine the influence of interactional torques on movement coordination. Explicitly defined combinations of elbow movements (ranging from 20 to 70°) and wrist movements (ranging from 20 to 40°) were performed during a visual, step-tracking task in which subjects were specifically required to attend to the initial and final angles at each joint. In all conditions the wrist and elbow rotated in the same direction, that is, flexion-flexion or extension-extension. Elbow movement kinematics were only slightly influenced by motion about the wrist. In contrast, the trajectory of the wrist movement was significantly influenced by uncompensated reaction torques resulting from movement about the elbow joint. At any given wrist amplitude, wrist movement duration increased and peak velocity decreased as elbow amplitude increased. In addition, as elbow amplitude increased, wrist movement on-set was progressively delayed relative to this elbow movement. Surprisingly, the changes between joint movement onsets were not accompanied by corresponding changes between agonist EMG onsets at the elbow and wrist joints. The mean difference in onset times between elbow and wrist agonists (22–30 ms) remained unchanged across conditions. In addition, a basic pattern of muscle activation that scaled with movement amplitude was observed at each joint. Phasic agonist activity at the wrist and elbow joints remained remarkably similar across conditions and thus the changes in joint movement onset could not be attributed to changes in the motor commands. Rather, the calculated torques from the averaged data showed that the difference in timing of joint movement onsets was influenced by joint interactional torques. These findings suggest that during simple two-joint planar movements of the elbow and the wrist joint, the central nervous system does not alter the basic motor commands at each joint and as a result the actual trajectory of each joint is determined by interactional torques.

Reprogramming of muscle activation patterns at the wrist in compensation for elbow reaction torques during planar two-joint arm movements.

The relationship between wrist kinematics, dynamics and the pattern of muscle activation were examined during a two-joint planar movement in which the two joints moved in opposite directions, i.e. elbow flexion/wrist extension and elbow extension/wrist flexion. Elbow movements (ranging from 10 to 70 deg) and wrist movements (ranging from 10 to 50 deg) were performed during a visual, step-tracking task in which subjects were required to attend to the initial and final angles at each joint. As the elbow amplitude increased, wrist movement duration increased and the wrist movement trajectories became quite variable. Analysis of the torques acting at the wrist joint showed that elbow movements produced reaction torques acting in the same direction as the intended wrist movement. Distinct patterns of muscle activation were observed at the wrist joint that were dependent on the relative magnitude of the elbow reaction torque in relation to the net wrist torque. When the magnitude of the elbow reaction torque was quite small, the wrist agonist was activated first. As the magnitude of the elbow reaction torque increased, activity in the wrist agonist decreased significantly. In conditions where the elbow reaction torque was much larger than the net wrist torque, the wrist muscle torque reversed direction to oppose the intended movement. This reversal of wrist muscle torque was directly associated with a change in the pattern of muscle activation where the wrist antagonist was activated prior to the wrist agonist. Our findings indicate that motion of the elbow joint is an important consideration in planning wrist movement. Specifically, the selection of muscle activation patterns at the wrist is dependent on the relative magnitude and direction of the elbow reaction torque in relation to the direction of wrist motion.

Effects of gravitational forces on single joint arm movements in humans

We have examined the kinematics and muscle activation patterns of single joint elbow movements made in the vertical plane. Movements of different amplitudes were performed during a visual, step-tracking task. By adjusting shoulder position, both elbow flexion and extension movements were made under three conditions: (a) in the horizontal plane, (b) in the vertical plane against gravity, and (c) in the vertical plane with gravity. Regardless of the gravitational load, all movements were characterized by time symmetric velocity profiles. In addition, no differences were found in the relationships between movement duration, peak velocity, and movement amplitude in movements with or against gravity. The pattern of muscle activation was influenced however, by the gravitational load. Both flexion and extension movements made with gravity were characterized by a reciprocally organized pattern of muscle activity in which phasic agonist activity was followed by phasic antagonist activity. Flexion and extension movements made against gravity were characterized by early phasic antagonist activity occurring at about the same time as the initial agonist burst. These findings suggest that EMG patterns are modified in order to preserve a common temporal structure in the face of different gravitational loads.

Evidence for outcomes of motivational rehabilitation interventions for children and adolescents with cerebral palsy: an American Academy for Cerebral Palsy and Developmental Medicine systematic review

This study reviewed evidence regarding the effect of motivational rehabilitation interventions on outcomes in children with cerebral palsy. Six databases were searched for literature published up to May 2012. Included studies measured the purported motivating effects of motor‐based rehabilitation interventions and the measured impact on outcomes. The American Academy for Cerebral Palsy and Developmental Medicine (AACPDM) systematic review methodology was used as a framework. Eight studies evaluated outcomes of studies using virtual reality interventions and one in a functional therapy context. Conflicting evidence from three (level II and level III) studies exists about the impact of these motivating interventions on motor outcomes measured in body functions. No statistical evidence regarding activity and participation outcomes exists. A single level II study found no significant difference in participants’ motivation between motivational and conventional interventions. This review revealed a paucity of research on the effects of motivational interventions. Weaknesses include a lack of consistency in the examination of motivational interventions, limited use of definitions or theories to ground the concept of motivation, and reliance on non‐validated methodological tools. This body of evidence would be strengthened by the use and development of robust outcome measures of motivation.

Children with Down syndrome: Discovering the joy of movement

JOPERD • Volume 77 No. 6 • August 2006 D own syndrome (DS) is the most frequently occurring chromosomal abnormality. It results from the presence of an extra partial or complete 21st chromosome. This increase in genetic material disrupts all aspects of an individual’s physical, mental, and social development. While the specifi c sensory and perceptual-motor impairments associated with DS have been well reported, less is known about how best to structure the environment and tailor programs that can maximize the potential of individuals with DS and increase their participation in physical activity. For children with DS, it is widely recognized that the development of movement patterns and the acquisition of motor skill profi ciency can be a slow and discouraging process. Although some children can attain a competence level that is somewhat comparable to their peers, motor milestones are generally delayed, and, in certain aspects of motor skill performance, children and adults with DS show a “lack of fi nesse” often described as “clumsy” (Henderson, 1986; Jobling 1999a, b; Latash, 2000). For children with DS, discovering the joy of movement can be a frustrating and diffi cult task. From a perceptual-motor perspective, the motor features of this observed “clumsiness” are “not straightforward...and sometimes puzzling” (Latash, 2000 p. 209). This awkward form of movement can add to feelings of frustration as movement and movement sequences in action become ineffi cient and thus ineffective as related to the task.

Changes in mu rhythm during action observation and execution in adults with Down syndrome : Implications for action representation

The human mirror neuron system is thought to be the underlying basis of perception-action coupling involved in imitation and action understanding. In order to examine this issue we examined the recruitment of the mirror neuron system, as reflected in mu rhythm suppression in a population of adults with Down syndrome (DS) with known strengths in imitation but with impairments in perceptual-motor coupling. Ten healthy adults and 10 age-matched adults with (DS) participated in the study. Subjects were asked to make self-paced movements (execution), and view movements made by the experimenter (observation). The action consisted of reaching with the dominant hand to grasp and lift a cup. Cortical responses were recorded with a whole head magnetoencephalography (MEG) system. Both groups demonstrated significant attenuation of the mu rhythm in bilateral sensorimotor areas when executing the action. Typical adults also demonstrated significant mu suppression in bilateral sensorimotor areas during observation of the action. In contrast, when observing the movement, adults with DS showed a significantly reduced overall attenuation of mu activity with a distinct laterality in the pattern of mu suppression. These results suggest that there is a dysfunction in the execution/observation matching system in adults with DS and has implications for the functional role of the human mirror neuron system.