Superior parietal cortex has been implicated in visuomotor guidance and is proposed to be specialised for action in the lower visual field and peripersonal space. Two patients, one with a right superior parietal lesion leading to optic ataxia (ME), and one with a lesion affecting right inferior parietal cortex (LH), were compared to elderly controls (n=8) and young controls (n=8) on a reciprocal pointing task with movements made in the near-far direction (i.e., sagittal plane) or right-left direction (i.e., fronto-parallel plane). In contrast to both control groups, who demonstrated a speed-accuracy trade-off in movement time and peak velocity, neither of the patients did. When the time spent post-peak velocity (represented as a percentage of total movement time) was examined, both patients demonstrated larger times post-peak velocity than controls for all movement directions. Furthermore, while rightward movements of the right hand had higher times post-peak velocity than leftward movements there were no directional patterns for near-far movements which contrasted with controls who had larger times post-peak velocity for near movements. The patient with the more superior lesion (ME) had the greatest difficulty with movements made back toward the body suggestive of a role for superior parietal cortex in the fine tuning of movements made in this region of space (i.e., personal or peripersonal space). In contrast, all directions of movement seemed to be equally affected in the patient with a more inferior lesion. These results are discussed in terms of the different roles played by inferior and superior parietal cortex in the control of visually guided movements.

Superior parietal cortex has been implicated in visuomotor guidance and is proposed to be specialised for action in the lower visual field and peripersonal space. Two patients, one with a right superior parietal lesion leading to optic ataxia (ME), and one with a lesion affecting right inferior parietal cortex (LH), were compared to elderly controls (n=8) and young controls (n=8) on a reciprocal pointing task with movements made in the near-far direction (i.e., sagittal plane) or right-left direction (i.e., fronto-parallel plane). In contrast to both control groups, who demonstrated a speed-accuracy trade-off in movement time and peak velocity, neither of the patients did. When the time spent post-peak velocity (represented as a percentage of total movement time) was examined, both patients demonstrated larger times post-peak velocity than controls for all movement directions. Furthermore, while rightward movements of the right hand had higher times post-peak velocity than leftward movements there were no directional patterns for near-far movements which contrasted with controls who had larger times post-peak velocity for near movements. The patient with the more superior lesion (ME) had the greatest difficulty with movements made back toward the body suggestive of a role for superior parietal cortex in the fine tuning of movements made in this region of space (i.e., personal or peripersonal space). In contrast, all directions of movement seemed to be equally affected in the patient with a more inferior lesion. These results are discussed in terms of the different roles played by inferior and superior parietal cortex in the control of visually guided movements.

Although several studies have investigated the effects of aging on aspects of motor planning and control, there remains a lack of consensus about the underlying mechanisms responsible for the motor slowing associated with aging. This may, at least partially, be due to the fact that few studies have kinematically examined both the transport and grasp components in both younger and older adults, and furthermore, even fewer have examined these movements when the context of the task is changed, such as when the movement is performed in isolation compared to when it is embedded in a sequence. Therefore, the purpose of this thesis was threefold: 1) to investigate how aging affects performance on a single reach-to-grasp movement, 2) to examine how movement context affects performance on the reach-to-grasp movement when it is performed alone or as the first movement in a two-movement sequence- in other words, are older adults able to plan the first motor task movement in anticipation of performing a subsequent task, and 3) whether younger and older adults are able to plan, execute, and modify that movement in accordance with the extrinsic properties of the subsequent movement task (near versus far target for second movement). To address this, the movement profiles of both younger (N=14; mean age= 20.7 years; 4 males, 10 females) and older (N=11; mean age= 75.1 years; 3 males, 8 females) healthy right-handed adults were compared on performing a reach-to-grasp movement under 3 different movement conditions: single-movement task, two-movement sequence to near target, and two-movement sequence to far target. For the two-movement sequence conditions, participants were instructed to reach and grasp the object (like the single-movement task), but then to move and place it on either a closer (near condition) or farther (far condition) target location. Overall, the results from this study are in agreement with the literature showing older adults to have slower movements in general and consistently taking longer to both initiate and execute the reach-to-grasp movement than the younger adults for all conditions. There were no other differences between groups on the single-movement condition. For all participants, the reach-to-grasp movement took longer when it was performed in isolation than when it was embedded as the first part of a two-movement sequence. This finding can be explained by the movement termination effect and is consistent with findings from studies on aiming movements showing that when the movement plan involves stabilizing the arm at the first target (single-movement) as opposed to merely slowing it down (two-movement sequence tasks), the constraint of achieving a stabile position imposes a greater demand, thus requiring the movement iv to be made more slowly. The results obtained from the study indicate that the movement termination effect is also seen in the context of prehensile movements and furthermore, this effect on performance persists with age. Not only do the findings from this study show that this effect persists with age, but also that this effect increases with age, as revealed by a Group by Condition effect for reaction time, movement time, and relative timing of the velocity profile, indicating greater changes in reaching performance between single- and two-movement conditions for the older adults than for the younger adults. Upon further examination of the details of the movement, it is apparent this movement termination effect is reflected in the ballistic phase of the movement. This last notion is inconsistent with previous studies, which showed the increased movement time associated with the movement termination effect was the result of changes in the amount of time spent in the deceleration phase toward the end of the movement rather than the beginning of the movement. Lastly, when reach-to-grasp performance was compared between moving to a near- compared to a far-target in the two-movement conditions, no differences were found between any of the movement features for either group. This suggests that the increased proportion of time spent in deceleration for the dual-movement conditions compared to the single-movement condition in older adults is due to online feedback control for terminating the first movement rather than online planning of the second movement. Despite the changes seen in the transport component, the findings for the manipulation component indicate that the formation of the grasp and its relative coupling with the transport component remains intact with age.

Movement and memory are two of the most fundamental components of our existence. From the moment of birth, we rely on a variety of movements to interact with people and objects around us, and as we grow, we continuously form new motor memories to improve the fidelity of these interactions by exploring and learning more about our environment, especially in unfamiliar situations, ultimately becoming better equipped to handle novel and unknown environments. In this dissertation, we explore four facets of motor memory associated with voluntary movement and postural control in the upper limbs: (1) Optimal motor memory formation via sensorimotor integration. We ask whether the motor system combines prior memories with new sensory information to produce statistically-optimal weight estimates. We find that the weight estimate that the motor system makes in order to re-stabilize one’s arm posture when an object is rapidly removed from the hand that supports it, reflected information integration in a Bayesian, statistically-optimal fashion. Remarkably, we demonstrate that when experiencing the well-known size-weight illusion, the motor and perceptual system’s weight estimates are biased in opposite directions, suggesting two divergent modes for information integration within the central nervous system. (2) Movement features important for the learning and generalization of motor memories. We show that, velocity-dependent adaptation generalizes across different movements, even from discrete straight point-to-point to continuous circular movements, however the amount of generalization is limited and context-dependent. In a series of experiments, we quantified the contributions of different movement features to the elicited adaptation transfer. In particular, we show that other movement states (i.e. position and acceleration) make only minor contributions whereas, the contexts provided by movement geometry and movement continuity are critical. (3) Internal representation of motor memories in intrinsic-extrinsic coordinates. We show that motor memories are based not on fully intrinsic or extrinsic representations but on a gain-field (multiplicative) combination the two. This gain-field representation generalizes between actions by effectively computing movement similarity based on the Mahalanobis distance across both intrinsic and extrinsic coordinates, in line with neural recordings showing mixed intrinsic-extrinsic representations in motor and parietal cortices. (4) Motor memories with local and global generalization. We demonstrate the existence of two distinct components of motor memory displaying different generalization footprints: One generalizes only locally, around the trained movement direction and with the trained end-effector, whereas the other generalizes broadly across both., We proceed to show that broad generalization results from a rapidly-learning adaptive process, dominates on easier-to-learn tasks, and performs high-level processing, producing adaptation vectors that integrate multiple sources of information, in line with a recent theory for perceptual learning. / Engineering and Applied Sciences

The study of visually-guided reaching has been a meaningful tool to investigate sensory-motor coordination in typical development and different clinical paediatric populations. The aim of this study was to characterize the development of multi-joint reaching behaviour in children and youth, from 5 to 16 years of age, allowing us to capture changes that may occur into adolescence. Participants were 68 able-bodied children and youth, with no history of developmental, educational or social problems. A stratified recruitment strategy was used to adequately represent five age groups: I (5-6 years), II (7-8 years), III (9-10 years), IV (11-13 years) and V (14-16 years). A center-out reaching task was used as it allowed us to measure effects of limb mechanics during reaching. Different patterns of inter-segmental motions at the shoulder and elbow joints were needed to reach the different targets: flexion at both joints, extension at both joints, and a mixed-coordination pattern. Children were asked to reach quickly and accurately to 8 targets located at 45 degree intervals around the perimeter of a circle with a 6 cm radius. The development of reaching was described using non-parametric statistics. The global features of path length and total movement decreased as a function of increasing age, with less variability observed in older participants (p<0.05). This increased accuracy was explained by a significant reduction (p<0.05) in distance and direction error of the first movement component of the reach, indicative of the increasing ability of children to accurately plan movements based on an internal representation of the limb. These older children were also able to respond to the visual target more quickly (p<0.05). In general, initial direction errors and total movement time increased from a minimum for the 2-joint flexion coordination to a maximum for the mixed-coordination pattern. The magnitude of error, however, decreased as a function of age (p<0.05), and in particular for the mixed-coordination pattern (p<0.01). This center-out task is therefore considered to be responsive to observe effects of development and limb mechanics on performance. The established normative data set will provide a reference for the measures of performance in children with neurodevelopmental disorders. / Thesis (Master, Rehabilitation Science) -- Queen's University, 2009-11-30 11:29:28.718

Although several studies have investigated the effects of aging on aspects of motor planning and control, there remains a lack of consensus about the underlying mechanisms responsible for the motor slowing associated with aging. This may, at least partially, be due to the fact that few studies have kinematically examined both the transport and grasp components in both younger and older adults, and furthermore, even fewer have examined these movements when the context of the task is changed, such as when the movement is performed in isolation compared to when it is embedded in a sequence. Therefore, the purpose of this thesis was threefold: 1) to investigate how aging affects performance on a single reach-to-grasp movement, 2) to examine how movement context affects performance on the reach-to-grasp movement when it is performed alone or as the first movement in a two-movement sequence- in other words, are older adults able to plan the first motor task movement in anticipation of performing a subsequent task, and 3) whether younger and older adults are able to plan, execute, and modify that movement in accordance with the extrinsic properties of the subsequent movement task (near versus far target for second movement). To address this, the movement profiles of both younger (N=14; mean age= 20.7 years; 4 males, 10 females) and older (N=11; mean age= 75.1 years; 3 males, 8 females) healthy right-handed adults were compared on performing a reach-to-grasp movement under 3 different movement conditions: single-movement task, two-movement sequence to near target, and two-movement sequence to far target. For the two-movement sequence conditions, participants were instructed to reach and grasp the object (like the single-movement task), but then to move and place it on either a closer (near condition) or farther (far condition) target location. Overall, the results from this study are in agreement with the literature showing older adults to have slower movements in general and consistently taking longer to both initiate and execute the reach-to-grasp movement than the younger adults for all conditions. There were no other differences between groups on the single-movement condition. For all participants, the reach-to-grasp movement took longer when it was performed in isolation than when it was embedded as the first part of a two-movement sequence. This finding can be explained by the movement termination effect and is consistent with findings from studies on aiming movements showing that when the movement plan involves stabilizing the arm at the first target (single-movement) as opposed to merely slowing it down (two-movement sequence tasks), the constraint of achieving a stabile position imposes a greater demand, thus requiring the movement iv to be made more slowly. The results obtained from the study indicate that the movement termination effect is also seen in the context of prehensile movements and furthermore, this effect on performance persists with age. Not only do the findings from this study show that this effect persists with age, but also that this effect increases with age, as revealed by a Group by Condition effect for reaction time, movement time, and relative timing of the velocity profile, indicating greater changes in reaching performance between single- and two-movement conditions for the older adults than for the younger adults. Upon further examination of the details of the movement, it is apparent this movement termination effect is reflected in the ballistic phase of the movement. This last notion is inconsistent with previous studies, which showed the increased movement time associated with the movement termination effect was the result of changes in the amount of time spent in the deceleration phase toward the end of the movement rather than the beginning of the movement. Lastly, when reach-to-grasp performance was compared between moving to a near- compared to a far-target in the two-movement conditions, no differences were found between any of the movement features for either group. This suggests that the increased proportion of time spent in deceleration for the dual-movement conditions compared to the single-movement condition in older adults is due to online feedback control for terminating the first movement rather than online planning of the second movement. Despite the changes seen in the transport component, the findings for the manipulation component indicate that the formation of the grasp and its relative coupling with the transport component remains intact with age.

abstract: The ability to plan, execute, and control goal oriented reaching and grasping movements is among the most essential functions of the brain. Yet, these movements are inherently variable; a result of the noise pervading the neural signals underlying sensorimotor processing. The specific influences and interactions of these noise processes remain unclear. Thus several studies have been performed to elucidate the role and influence of sensorimotor noise on movement variability. The first study focuses on sensory integration and movement planning across the reaching workspace. An experiment was designed to examine the relative contributions of vision and proprioception to movement planning by measuring the rotation of the initial movement direction induced by a perturbation of the visual feedback prior to movement onset. The results suggest that contribution of vision was relatively consistent across the evaluated workspace depths; however, the influence of vision differed between the vertical and later axes indicate that additional factors beyond vision and proprioception influence movement planning of 3-dimensional movements. If the first study investigated the role of noise in sensorimotor integration, the second and third studies investigate relative influence of sensorimotor noise on reaching performance. Specifically, they evaluate how the characteristics of neural processing that underlie movement planning and execution manifest in movement variability during natural reaching. Subjects performed reaching movements with and without visual feedback throughout the movement and the patterns of endpoint variability were compared across movement directions. The results of these studies suggest a primary role of visual feedback noise in shaping patterns of variability and in determining the relative influence of planning and execution related noise sources. The final work considers a computational approach to characterizing how sensorimotor processes interact to shape movement variability. A model of multi-modal feedback control was developed to simulate the interaction of planning and execution noise on reaching variability. The model predictions suggest that anisotropic properties of feedback noise significantly affect the relative influence of planning and execution noise on patterns of reaching variability. / Dissertation/Thesis / Ph.D. Bioengineering 2012

The relationship between the development of sitting postural control and of reaching during infancy has not been addressed in detail. It has recently been shown that trunk control develops starting with the head, then the upper trunk and subsequently the lower/pelvic regions. However, previous studies on infant reaching evaluated infants during supported supine or reclined sitting positions, failing to address the contributions of distinct regions of the trunk to reaching. This dissertation explores the relationship between the progression of trunk control and reaching performance in healthy infants. The effects of stabilizing the upper and lower regions of the trunk were assessed by providing vertical trunk fixation at two levels of support (thoracic and pelvic). Documentation of postural and reaching performance reflected how control of the free regions of the trunk modulated both behaviors. First, kinematic data were collected in infants aged 4-6 months who were grouped according to their sitting ability and extent of trunk control. Second, a longitudinal study was implemented in which kinematic and electromyographic recordings were collected bi-monthly from 2.5-8 months. Results from the cross-sectional study showed that postural stability and reaching kinematics of the two groups were similar when they received support at the thoracic level but differed when the support was limited to the pelvic level. Infants who were able to sit independently outperformed the infants who were unable to sit without help. These data were further expanded with the results obtained from the longitudinal study, showing that during the months prior to independent sitting, infant reaches were impoverished and were associated with a lack of postural stability when provided with pelvic, in comparison to thoracic, support. In addition, infants displayed inefficient muscle patterns in response to the instability. Differences between levels of support were not observed once infants acquired independent sitting. Taken together, these results offer detailed measures of the progression of trunk control and its relation to reaching. This raises important questions regarding whether this more specific approach may create the foundation for evaluating and improving trunk control in atypically developing populations. This dissertation includes previously published and unpublished co-authored material.

abstract: Understanding where our bodies are in space is imperative for motor control, particularly for actions such as goal-directed reaching. Multisensory integration is crucial for reducing uncertainty in arm position estimates. This dissertation examines time and frequency-domain correlates of visual-proprioceptive integration during an arm-position maintenance task. Neural recordings were obtained from two different cortical areas as non-human primates performed a center-out reaching task in a virtual reality environment. Following a reach, animals maintained the end-point position of their arm under unimodal (proprioception only) and bimodal (proprioception and vision) conditions. In both areas, time domain and multi-taper spectral analysis methods were used to quantify changes in the spiking, local field potential (LFP), and spike-field coherence during arm-position maintenance. In both areas, individual neurons were classified based on the spectrum of their spiking patterns. A large proportion of cells in the SPL that exhibited sensory condition-specific oscillatory spiking in the beta (13-30Hz) frequency band. Cells in the IPL typically had a more diverse mix of oscillatory and refractory spiking patterns during the task in response to changing sensory condition. Contrary to the assumptions made in many modelling studies, none of the cells exhibited Poisson-spiking statistics in SPL or IPL. Evoked LFPs in both areas exhibited greater effects of target location than visual condition, though the evoked responses in the preferred reach direction were generally suppressed in the bimodal condition relative to the unimodal condition. Significant effects of target location on evoked responses were observed during the movement period of the task well. In the frequency domain, LFP power in both cortical areas was enhanced in the beta band during the position estimation epoch of the task, indicating that LFP beta oscillations may be important for maintaining the ongoing state. This was particularly evident at the population level, with clear increase in alpha and beta power. Differences in spectral power between conditions also became apparent at the population level, with power during bimodal trials being suppressed relative to unimodal. The spike-field coherence showed confounding results in both the SPL and IPL, with no clear correlation between incidence of beta oscillations and significant beta coherence. / Dissertation/Thesis / Doctoral Dissertation Biomedical Engineering 2017

Successful coordination of prehensile action depends upon the selection and control of appropriate reach and grasp movements. This thesis explores how prehensile actions are shaped and regulated by perceptual information. According to ecological psychology, behaviour is achieved through the detection of information specifying the opportunities the environment affords for action. A review of the literature identified that as this information evolves over time, a comprehensive understanding of prehension has to consider how affordance perception and continual guidance of action come together in the pursuit of goal-directed action. In a series of interlinking studies the initiation, hand transport and grasp components of prehension were investigated in order to determine how affordances are manifested in the emergence of, and guidance within, prehensile actions. Study 1 explored the effect of information specifying affordances on the time taken to initiate and perform a ball-posting action. Results indicated that affordance perception was reflected in initiation time, whilst affordance actualisation was reflected in movement time, demonstrating that effects of affordance perception extend beyond action preparation to directly influence the emergence of action. Study 2 investigated the selection and regulation of perceptual information during the guidance of hand transport. General tau theory (Lee, 1998) was applied to test i) whether the ratio of coupling between hand and object motion is held constant throughout the reach, and ii) whether this ratio, k, describes the kinematics of handobject contact under varying spatiotemporal task constraints. Results indicated a constant tau ratio during the middle, but not the end phase of the movement; moreover, although the summary ratio k was not sensitive to task manipulations, the time-dependent counterpart, K(t), did exhibit effects of task constraints. This indicates that the guidance of hand transport was a continuous process, where, dependent upon the task goals, the regulation of perceptual information changed throughout the action. The final study, Study 3, examined digit coordination during the grasp. Focusing on the transition from 2-digit to 3-digit grip configurations, the study addressed whether grip selection is made before or during the action. Results showed the transition between 2- and 3-digit grips occurs at a within trial level. The grip configuration utilised could only be distinguished as 2- or 3-digit during the second half of the movement, indicating that grip selection emerges online during the unfolding action. Together these studies provide evidence of continual guidance of prehensile actions and offer support for the consideration of prehensile action as a set of nested task goals. It was concluded that affordance perception and movement guidance are interrelated and evolve continuously throughout the unfolding prehensile action. In light of these findings, issues relating to action selection emerging online from the organism-environment interaction are discussed.