The Effects of Systematic Environmental Manipulation on Gait of Older Adults.

Quantification of gait changes in response to altered environmental stimuli may allow for improved understanding of the mechanisms that influence gait changes and fall occurrence in older adults. This study explored how systematic manipulation of a single dimension of one's environment affects spatiotemporal gait parameters. A total of 20 older adult participants walked at a self-selected pace in a constructed research hallway featuring a mobile wall, which allowed manipulation of the hallway width between three conditions: 1.14 m, 1.31 m, and 1.48 m. Spatiotemporal data from participants' walks were captured using an instrumented GAITRite mat. A repeated measures ANOVA revealed older adults spent significantly more time in double support in the narrowest hallway width compared to the widest, but did not significantly alter other spatiotemporal measures. Small-scale manipulations of a single dimension of the environment led to subtle, yet in some cases significant changes in gait, suggesting that small or even imperceptible environmental changes may contribute to altered gait patterns for older adults.

Interlimb Coordination During a Combined Gait and Prehension Task.

Reaching and grasping are often completed while walking, yet the interlimb coordination required for such a combined task is not fully understood. Previous studies have produced contradictory evidence regarding preference for support of the lower limb ipsilateral or contralateral to the upper limb when performing a reaching task. This coordinative aspect of the combined task provides insight into whether the two tasks are mutually modified or if the reach is superimposed upon normal arm swinging. Collectively, 18 right-handed young adults walked slower, took shorter steps, and spent more time in double support during the combined task compared with walking alone. The peak grasp aperture was larger in walking reach-to-grasp trials compared with standing trials. There was not a strong trend for lower limb support preferences at the reach initiation or object contact. The participants could begin walking with either foot and demonstrated variability of preferred gait initiation patterns. There was a range of interlimb coordination patterns, none of which could be generalized to all young adults. The variability with which healthy right-handed young adults execute a combined walking reach-to-grasp task suggests that the cyclical (walking) and discrete (prehension) motor tasks may have separate motor control mechanisms, as proposed in the two primitives theory.

Biofeedback-Based, Videogame Balance Training in Autism.

The present study examined the effects of a visual-based biofeedback training on improving balance challenges in autism spectrum disorder (ASD). Twenty-nine youth with ASD (7-17 years) completed an intensive 6-week biofeedback-based videogame balance training. Participants exhibited training-related balance improvements that significantly accounted for postural-sway improvements outside of training. Participants perceived the training as beneficial and enjoyable. Significant moderators of training included milder stereotyped and ritualistic behaviors and better starting balance. Neither IQ nor BMI moderated training. These results suggest that biofeedback-based balance training is associated with balance improvements in youth with ASD, most robustly in those with less severe repetitive behaviors and better starting balance. The training was perceived as motivating, further suggesting its efficacy and likelihood of use.

Bimanual Reach to Grasp Movements in Youth With and Without Autism Spectrum Disorder.

Reaching and grasping (prehension) is one of the earliest developing motor skills in humans, but continued prehension development in childhood and adolescence enables the performance of increasingly complex manual tasks. In individuals with autism spectrum disorder (ASD) atypical unimanual reaching and grasping has been reported, but to date, no studies have investigated discrete bimanual movements. We examined unimanual and bimanual reach to grasp tasks in youth with ASD to better understand how motor performance might change with increasing complexity. Twenty youth with ASD (10.1 ± 2.4 years) and 17 youth with typical development (TD) (9.6 ± 2.6 years) were instructed to reach and grasp cubes that became illuminated. Participants were asked to reach out with the right and/or left hands to grasp and lift targets located at near (18 cm) and/or far (28 cm) distances. For the unimanual (simplest) condition, participants grasped one illuminated cube (with either the left or right hand). For the bimanual conditions, participants grasped two illuminated cubes located at the same distance from the start position (bimanual symmetric condition) or two illuminated cubes located at different distances (bimanual asymmetric condition). Significant interactions among diagnostic group, task complexity, and age were found for initiation time (IT) and movement time (MT). Specifically, the older children in both groups initiated and performed their movements faster in the unimanual condition than in the bimanual conditions, although the older children with ASD produced slower ITs and MTs compared to typically developing peers across all three conditions. Surprisingly, the younger children with ASD had similar ITs and MTs as their peers for the unimanual condition but did not considerably slow these times to adjust for the complexity of the bimanual tasks. We hypothesize that they chose to re-use the motor plans that were generated for the unimanual trials rather than generate more appropriate motor plans for the bimanual tasks. An atypical spatiotemporal relationship between MT and peak aperture (PA) was also found in the ASD group. Together, our results suggest deficits in motor planning that result in subtle effects on performance in younger children with ASD that become more pronounced with age.

The effect of endpoint congruency on bimanual transport and rotation tasks.

The completion of many goal oriented skills requires the tight coordination of the right and left hands to achieve the task objective. Although the coordination of wrist transport and orientation of the hand before object contact has been studied in detail for discrete bimanual tasks, as yet, very few studies have examined bimanual coordination when the target is already in hand. It has been shown that congruency of the goal facilitates the production of discrete bimanual responses. The purpose of this study was to investigate the role of goal congruency on precision bimanual transport and rotate tasks. In the current investigation, participants transported two cubic objects while rotating them laterally to place them into tight-fitting targets. The magnitude of the rotation could be the same for both hands (i.e., both 45 or 90(∘)) or different (i.e., one 45 and 90(∘)) and the endpoint orientations (i.e., goal) could either be congruent or incongruent. Results indicated that when the endpoint orientation was congruent for the two hands, movement times were similar regardless of hand (left or right), rotation magnitude (45, 90(∘)) and whether the rotation magnitude for the two hands was the same or different. These results suggest that congruency of the endpoint goal facilitates the temporal synchronization of the transport component for two limbs. In contrast, a different pattern of results was obtained when considering the rotation component. Specifically, regardless of whether the hands were rotating the same magnitude or ending in congruent endpoint positions, the coordination of the rotation component between the hands was asynchronous. We hypothesize that the greater requirement to shift visual fixation from one hand/target to the other to ascertain the separate goal orientations may explain these differences. These results provide further evidence that multiple constraints act to influence the performance of skilled bimanual tasks.

Bimanual coordination in children: manipulation of object distance.

The performance of many everyday activities requires the coordination of the two upper limbs to achieve the goal of the task. Although bimanual performance has been studied in detail in adults, few studies have examined how children coordinate the movements of the two hands during symmetric and asymmetric bimanual prehension. With the current study, we asked younger (4-6 years, n = 14) and older (7-10 years, n = 16) children to complete a discrete bimanual task. Specifically, they reached to grasp cylinders located at near and far positions in either unimanual or bimanual condition. During bimanual symmetric conditions, participants performed movements with both hands toward two objects located at the same distance (both near or both far), while in the bimanual asymmetric conditions, they reached for objects at different distances. Results of the kinematic analyses indicated that the young children consistently experienced the "two target" effect, whereby bimanual movements were executed more slowly than unimanual movements to the same distance. Older children employed a hybrid strategy, exhibiting slower movements in bimanual congruent conditions, but larger non-dominant apertures in bimanual incongruent conditions. This hybrid strategy was hypothesized to stem from developmental changes occurring in the integration of sensory information around 8 years of age. While older children exhibited temporal and spatial coordination patterns that were similar to patterns reported in adults, large relative timing differences at the start and end of bimanual movements and considerably weaker spatial coupling were seen in the younger children.

Bimanual coordination affects motor task switching.

Task-switching paradigms have generally been used to investigate cognitive processes involved in decision making or allocating attention. This work extended the task-switching paradigm into the motor domain in order to investigate the consequences of an unexpected environmental perturbation on reaction time and movement time. Typically, task-switching paradigms have investigated consequences of rearranging task sets from one trial to the next; this work explored rearranging planned movements within the context of a single trial. Of particular interest was how the motor system reorganizes coordination patterns when reaching amplitude congruency is manipulated between the two hands. Results for Experiment 1 and the far distance in Experiment 2 indicated that reaction time switch costs were the smallest during congruent task-switch trials, where reaching amplitudes between the two hands were the same. This implies that a planned movement parameter for one hand is accessible for the other hand in the circumstance of an unexpected task switch. However, the reversed congruency effects found for the near distance in Experiment 2 suggest that the ability to capitalize on stored parameter information to decrease reaction time is dependent on environmental factors and task instructions. Movement time results showed that even if a movement with one hand is aborted in mid-execution, it can still influence the performance of the other hand during a task switch. This suggests that bimanual coordination can affect prehensile performance even though only one hand has a goal to achieve.

Perturbation of object location during bimanual prehension: the role of visual feedback.

In this series of studies on the coordination of the two hands during a bimanual perturbation task, 10 right-handed volunteers were asked to reach to grasp and lift two illuminated cubic objects. Upon initiation of the reach a perturbation could occur by extinguishing one or both objects and illuminating new objects located directly away from the start position in the para-sagittal plane (Experiment 1) or toward the start position in the para-sagittal plane (Experiment 2). In Experiment 2 we also manipulated position of the targets within the visual span by having the targets move toward the midline or away from the midline. Dependent measures included kinematic data for the reach movement as well as the timing of eye movements. Results of both experiments indicated little interference between the hands when one object was perturbed while the other remained stationary. We hypothesize that when visual feedback about limb movement is available, participants can independently reorganize the trajectory of the perturbed limb with minimal interference on the non-perturbed limb. Furthermore, results of Experiment 2 indicated that the position of the targets within the visual span at the final target location dictates the number of eye movements made to acquire both targets and can lead to asynchronies at movement termination in a task-dependent manner. Finally, we found that when targets were perturbed away from the body movement time results indicated a right-hand advantage for dealing with a single perturbation. In contrast, perturbations toward the body abolished the movement time advantage. We suggest that differences in the use of visual feedback when working in the upper versus lower visual fields may influence hand advantages.

Bimanual coordination in children: manipulation of object size.

An experiment was designed to investigate the temporal and spatial couplings of the transport and grasp components for bimanual movements performed by children. Thirty-one participants aged 4-6 (younger) and 7-10 (older) performed the unimanual task of reaching for, grasping, and lifting a small or large cylinder with the right or left hands or the bimanual task of reaching for, grasping and lifting two small cylinders, two large cylinders, or one small and one large cylinder with the right and left hands. Kinematic measures, relative timing differences between the hands, spatial plots and cluster analysis were used to quantify both temporal and spatial couplings of the limbs. While average kinematic results indicated that children in the 4-6 and 7-10 age range performed bimanual movements similarly to each other, spatio-temporal coupling measures indicated that the younger children performed the bimanual movements in a more sequential (serial) fashion. Kinematic results also indicated that the cost of the increase in task complexity normally seen in adults when grasping two targets bimanually compared to a single target unimanually are not consistently present for children. Instead, the cost associated with increases in task complexity appear to be mediated by whether the bimanual task imposes significantly greater demands on attentional processes. These results indicate that attention demands of the task as well as the intrinsic dynamics of the individual determine the degree of interlimb coupling of children during bimanual reach-to-grasp of different-sized objects.

Temporal coordination during bimanual reach-to-grasp movements: the role of vision.

The performance of bimanual movements involving separate objects presents an obvious challenge to the visuo-motor system: Visual feedback can only be obtained from one target at a time. To overcome this challenge overt shifts in visual attention may occur so that visual feedback from both movements may be used directly (Bingham, Hughes, & Mon-Williams, 2008; Riek, Tresilian, Mon-Williams, Coppard, & Carson, 2003). Alternatively, visual feedback from both movements may be obtained in the absence of eye movements, presumably by covert shifts in attention (Diedrichsen, Nambisan, Kennerley, & Ivry, 2004). Given that the quality of information falls with increasing distance from the fixated point, can we obtain the level of information required to accurately guide each hand for precision grasping of separate objects without moving our eyes to fixate each target separately? The purpose of the current study was to examine how the temporal coordination between the upper limbs is affected by the quality of visual information available during the performance of a bimanual task. A total of 11 participants performed congruent and incongruent movements towards near and/or far objects. Movements were performed in natural, fixate-centre, fixate-left, and fixate-right vision conditions. Analyses revealed that the transport phase of incongruent movements was similar across vision conditions for the temporal aspects of both the transport and grasp, whereas the spatial aspects of grasp formation were influenced by the quality of visual feedback. We suggest that bimanual coordination of the temporal aspects of reach-to-grasp movements are not influenced solely by overt shifts in visual attention but instead are influenced by a combination of factors in a task-constrained way.

Manual asymmetries in bimanual prehension tasks: manipulation of object size and object distance.

Two experiments were designed to investigate the temporal and spatial couplings of the transport and grasp components for bimanual movements to both congruent and incongruent targets. We studied conditions where task requirements were largely different for the two hands. Ten participants performed Experiment 1 and were required to reach for, grasp, and lift two small (1 mm) cylinders, two large (70 mm) cylinders, or one small and one large cylinder with the right and left hands. In Experiment 2, 10 participants were required to reach for, grasp, and lift two objects that were positioned either near (50mm) the start mark, far (maximum comfortable reaching distance) from the start mark, or one near and one far from the start mark. Kinematic measures, relative timing differences between the hands and spatial plots were used to quantify both temporal and spatial couplings of the limbs. For temporal coupling, the results from both experiments indicated that the upper limbs were controlled independently with some execution-level interference occurring for the transport component only. In terms of spatial coupling our results indicated weak coupling of the grasp component regardless of task parameters (i.e., congruent or incongruent movements) and a dependence on task parameters in determining the level of spatial coupling for the transport component. These results can be collectively interpreted as evidence for a functional coupling of the upper limbs. That is, the movements of the hands may be coupled during tasks in which temporal and spatial synchronizations are beneficial for performance. However, if the coupling of the upper limbs is either unimportant or perhaps even detrimental to the coordination of the overall movement, then the upper limbs may perform the desired movements independently of one another.

Coordination and control of bimanual prehension: effects of perturbing object location.

The purpose of the present study was to investigate the coordination of the two effectors when one or both targets were displaced in a bimanual prehension task. Sixteen right-handed volunteers were asked to reach 20 cm to grasp and lift two cubic objects with the right and left hands. Upon initiation of the reach: (1) both objects could remain at the initial position (NN); (2) the right object could be displaced toward the subject (NJ); (3) the left object could be displaced (JN); or (4) both objects could be displaced (JJ). Generally, the results indicated that the hand moving to the perturbed object was reorganized to reach the target efficiently, but hovered to somewhat couple object lift for the two hands. In contrast, adjustments were seen in the velocity profiles of the hand moving to the non-perturbed target, including a premature deceleration phase and corrective movements to reach the target location. Together, these results indicate that when the perturbation of one object occurs during the performance of a bimanual prehension task, visual information is used to independently update the control process for the limb moving to the perturbed object. Additionally, interference causes the limb moving to the non-perturbed target to be inappropriately adjusted in response to the perturbation. Our results also indicated that perceptual and motor factors such as time allotted for the use of feedback and the direction of movement may play a role in the independence/dependence relationship between the hands during bimanual tasks. Furthermore, subjects' expectations about the performance and goal of the task could have a further influence on the level of interference seen during bimanual movements. Finally, despite interference effects which caused multiple accelerations and decelerations, the hand moving to the non-perturbed target still achieved the target location in the same movement time as during control conditions. This final result indicates the efficiency with which subjects can reorganize both limbs in the face of altered task requirements.

Performance of unimanual and bimanual multiphased prehensile movements.

By manipulating task action demands in 2 experiments, the author investigated whether the context-dependent effects seen in unimanual multiphase movements are also present in bimanual movements. Participants (N = 14) in Experiment 1 either placed or tossed objects into targets. The results indicated that the intention to perform a subsequent action with an object could influence the performance of an earlier movement in a sequence in both unimanual and bimanual tasks. Furthermore, assimilation effects were found when the subsequent tasks being performed by the 2 hands were incongruent. In Experiment 2, the author investigated in 12 participants whether planning in a multiphase movement includes some representation of the accuracy demands of the subsequent task. The accuracy demands of a subsequent task did not appear to influence initial movement planning. Instead, the present results support the notion that it is the action requirements of the subsequent movement that lead to context-dependent effects.

Grip forces when passing an object to a partner.

The goal of the present study was to investigate how grip forces are applied when transferring stable control of an object from one person to another. We asked how grip forces would be modified by the passer to (1) control for inertial forces as the object was transported toward the receiver and (2) control for the impending perturbation when the receiver made contact with the object. Twelve volunteers worked in pairs during this experiment. One partner, playing the role of passer, transported an object with embedded load cells forward or held the object at an interception location. The second partner, playing the role of receiver, waited at an interception location or reached toward the passed object. Kinematic results indicated that while passers performed a stereotypical movement, receivers were sensitive to the motion of the object as they reached to make contact. Grip force results indicated that passers' grip forces and grip/load force ratios were variable on a trial-to-trial basis, suggesting that a refined internal model of the passing task was not achieved within the timeframe of the experiment. Furthermore, a decoupling of the temporal and magnitude characteristics of the grip and inertial forces was noted in conditions where passers transported the object toward the receiver. During object transfer, it was noted that passers used visual feedback-based anticipatory control to precisely time initial grip force release, while somatosensory control was used by both the passer and receiver to precisely coordinate transfer rate.