The visual grasp reflex provides automatic orienting of gaze (the visual axis in space) to novel visual stimuli. Previous studies have demonstrated activation of neck muscles of awake monkeys appearing at a short fixed latency (55 to 95 ms) after visual target presentation, regardless of whether or when saccades are made. The purpose of these early visually-driven muscle activations may be to prime head rotation required as a part of the coordinated eye-head movement to the target. Similar orienting responses might be found for visually guided reaching. Here, we explore early visually-driven muscle activations of the human upper limb immediately preceding planar reaching movements. Subjects performed reaches towards small visual peripheral targets while upper limb kinematics were recorded and intramuscular electromyography was collected from four shoulder and elbow muscles. Subjects maintained their right hand at a central fixation marker that was extinguished for a gap period (200 ms) prior to appearance of a peripheral target. Subjects were instructed to reach to the target as quickly as possible. Some subjects exhibited a short burst of muscle activity (about 20 ms duration) time-locked to visual target onset. This burst occurred around 85 ms to 105 ms after target onset and preceded the onset of muscle activity associated with volitional arm motion by about 100 ms. Notably, this burst was dependent on target location: visually-driven muscle activity occurred in right shoulder extensor muscles for rightward targets and was absent for leftward targets. In order to better dissociate the visual burst from volitional motor activity, we employed a delay paradigm. No time-locked muscle activity was present in the delay task either after the target appeared or after the fixation marker was extinguished. This suggests that the visual burst is dependent on the imminence of voluntary movement and the laterality of the target. We conclude that the appearance of a visual target can result in short-latency activity on the arm musculature that is appropriate for orienting the arm to the target. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2007-09-27 09:42:55.337

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Everyday movements, such as reaching for a drink of water or typing on a keyboard highlight the relative ease with which we move and interact with our surroundings. However, the success of these skilled movements depends on the motor system’s ability to consider a variety of factors, such as the goal of the behavioral task, the surrounding environment and the physical properties of the musculoskeletal system. Recent theories of voluntary motor control, namely optimal feedback control, suggest that such skilled motor behavior is achieved through sophisticated feedback control. This thesis investigates one physiological implication of this theory. Specifically, we hypothesize that rapid feedback responses following mechanical perturbations possess many of the functional attributes thought to be reserved for voluntary control because these two systems have contributions from similar neural substrates (eg. motor areas in cortex). Our studies were specifically designed to investigate rapid feedback responses during the long-latency epoch, which occurs between 50-100ms following a mechanical perturbation. Consistent with our hypothesis, we found that the sophistication of the long-latency response rivals that of voluntary control. In our first study (Chapter 2) we examined if rapid feedback responses were sensitive to features of the end target. We found that muscle activity during the long-latency epoch was modulated by the size/shape of the end. In our second study (Chapter 3) we observed flexible responses in muscle activity during the long-latency epoch that reflected rapid ‘decisions’ during online control regarding how to navigate around obstacles in the environment as well as how to select amongst multiple potential goals. In our final study (Chapter 4) we examined if rapid feedback responses in the shortened muscle parallel the sophisticated responses observed in the lengthened muscle. We found that unloading a pre-excited muscle elicited sophisticated inhibitory responses, including knowledge of limb mechanics and rapid target selection, during the long-latency epoch that are comparable to the excitatory responses observed during loading. Taken together, the studies presented in this thesis demonstrate that the responses in the long-latency epoch reflect several functional attributes typically reserved for voluntary control. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2014-04-29 16:54:12.489

This dissertation aimed to investigate the relationship between posture and reaching in both healthy and pathological conditions, approaching the trunk as a multi-segmented structure. For this purpose, neuromuscular and kinematic profiles were recorded from trunk and arm during seated reaches providing mid-rib vs pelvic levels of trunk support. Healthy adults with mature postural and reaching abilities displayed invariant arm kinematics during the reach. However, participants displayed increased anticipatory control and earlier activation of cervical muscles with mid-rib support. Participants also presented increased compensatory responses of paraspinal muscles when responding to the increased trunk balance demands with pelvic support. Children with moderate/severe cerebral palsy (CP) cannot maintain an upright sitting position and thus cannot create a stable postural frame around which upper limb movements are planned and executed. A second set of studies examined postural and reaching characteristics in these children, while applying axillae, mid-rib or pelvic levels of support. Participants were classified according to their intrinsic level of trunk control as mild, moderate and severe. With higher levels of support children with moderate to severe impairments in trunk control showed improvements of head and trunk control along with enhanced reaching performance. Participants with mild trunk dysfunction were able to sit independently and thus did not demonstrate significant changes in postural and reaching proficiency across levels of external trunk support. Electromyographic profiles were more variable depending on the severity of intrinsic trunk control. Overall, participants in the mild group presented more refined timing mechanisms for both anticipatory (closer to reaching onset) and compensatory (reduced latency) postural adjustments during the reach across all levels of support. Participants in the moderate group displayed earlier muscle onsets and more efficient arm/trunk muscle amplitudes with higher levels of support. Participants in the severe group showed very limited capability of anticipatory control of paraspinal muscles, delayed muscle onsets and variable muscle amplitudes across levels of support. These results emphasize the complex neuro-anatomical nature of trunk control during reaching. Also, they highlight that inefficient postural control while sitting significantly impacts children with CP and trunk dysfunction. This dissertation includes previously unpublished co-authored material.

This dissertation aimed to investigate the relationship between posture and reaching in both healthy and pathological conditions, approaching the trunk as a multi-segmented structure. For this purpose, neuromuscular and kinematic profiles were recorded from trunk and arm during seated reaches providing mid-rib vs pelvic levels of trunk support. Healthy adults with mature postural and reaching abilities displayed invariant arm kinematics during the reach. However, participants displayed increased anticipatory control and earlier activation of cervical muscles with mid-rib support. Participants also presented increased compensatory responses of paraspinal muscles when responding to the increased trunk balance demands with pelvic support. Children with moderate/severe cerebral palsy (CP) cannot maintain an upright sitting position and thus cannot create a stable postural frame around which upper limb movements are planned and executed. A second set of studies examined postural and reaching characteristics in these children, while applying axillae, mid-rib or pelvic levels of support. Participants were classified according to their intrinsic level of trunk control as mild, moderate and severe. With higher levels of support children with moderate to severe impairments in trunk control showed improvements of head and trunk control along with enhanced reaching performance. Participants with mild trunk dysfunction were able to sit independently and thus did not demonstrate significant changes in postural and reaching proficiency across levels of external trunk support. Electromyographic profiles were more variable depending on the severity of intrinsic trunk control. Overall, participants in the mild group presented more refined timing mechanisms for both anticipatory (closer to reaching onset) and compensatory (reduced latency) postural adjustments during the reach across all levels of support. Participants in the moderate group displayed earlier muscle onsets and more efficient arm/trunk muscle amplitudes with higher levels of support. Participants in the severe group showed very limited capability of anticipatory control of paraspinal muscles, delayed muscle onsets and variable muscle amplitudes across levels of support. These results emphasize the complex neuro-anatomical nature of trunk control during reaching. Also, they highlight that inefficient postural control while sitting significantly impacts children with CP and trunk dysfunction. This dissertation includes previously unpublished co-authored material.

No description available.

<p>The purpose of this study was to investigate leaning behaviours when completing tasks with constrained reaches. A logistic regression was developed, with the input of individual subject anthropometry and specific task characteristics, and the resulting model was able to provide a very accurate prediction of when an individual would lean. The inputs to this model give insight into what factors are important in the decision making process when a worker chooses whether lean. The task hand locations with the longest reaches resulted in the most frequent choice to lean. Leaning appears to be particularly common, and important, with long reaching and pulling tasks that can reduce task hand shoulder and trunk loads and improve balance, while allowing the worker to get closer to the task. Leaning hand forces were highest during pulling tasks. These findings are very important to document, as current ergonomic tools neglect to consider that different task characteristics may change how, and when, a worker leans. Even when only the direction of the task hand force was changed, leaning hand forces differed significantly. In this study, leaning hand height was slightly higher for the shoulder height, when compared to the umbilical height, task hand locations. The average height of the leaning hand did not vary considerably and ranged between 106.6cm to 116.3cm, depending on the condition. The leaning hand force magnitude changed as task hand location, force direction and force level changed. Leaning hand forces increased with increasing task hand load. Task hand forces in the push direction were higher compared to push and down exertions, regardless of task hand location or task hand load. The findings from this study are of particular use to industry as ergonomists now have representative forces and heights, to help guide leaning estimates during proactive risk assessments.</p> / Master of Science (MSc)

This thesis investigates how adults, infants, and children use visual information to control reaching movements. To do this, the kinematics of a reaching movement were recorded using a 6 camera motion tracking system. Adult reaching movements were investigated in three different experiments. The first experiment looked at the effect of visual information about the reach space and the target on reaching movements. Adult reaches are significantly affected by removal of visual information about the reach space and the target, e.g. peak speed decreases as distance information is occluded. Adult reaching movements are also affected by the length of the delay between viewing an object and then reaching for it in complete darkness. Experiment 2 reveals that there is a linear increase in movement duration, decrease in peak speed, and increase in maximum grip aperture with increasing temporal delay. This is due to the decay of dorsal visual information. Experiment 3 found that a cautious reaching movement can be defined as a reach where duration increases, average speed decreases, and peak timing is proportionally earlier in the reach. The three developmental experiments investigated the changes in reaching in infancy, in typically developing 5-year-old children, and in children with Williams syndrome (WS). Between 9 and 16 months of age, infants develop better coordination of reaching movements. Improved dark reaching behaviour in 16-month-olds may be associated with more mature processing in the dorsal visual stream. Reaching movements in 5-year-old children are straighter and faster than infant reaches but behaviour is not yet stereotyped like adults. WS children generate reaches that are slower and incorporate more movement units than 5-year-old children, and WS behaviour may reflect poor processing of dorsal visual information rather than poor control of arm movement.

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No description available.