Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: James C. Galloway, Dept. of Physical Therapy. Includes bibliographical references.

Performing goal-directed hand-movements in the presence of obstacles is a task that we usually complete successfully many times a day without much conscious consideration. Yet, little is known about the underlying processes. The aim of this thesis was to investigate the role of perceptual, motor and cognitive constraints on obstacle avoidance during reaching. To do this a tabletop-based obstacle avoidance setup and motiontracking were used. In the first experimental chapter, the previously reported tendency of participants to select movement paths that pass roughly through the mid-point between two obstacles was examined. The starting position of the hand and the availability of visual feedback were manipulated and evidence was found that movement path selection depends on both a collision-avoidance strategy and the associated biomechanical costs; even when visual feedback is unavailable. The second experimental chapter investigated an action-blindsight phenomenon, specifically the ability of cortically blind patients to avoid unseen obstacles. It was found that only two out of the six patients tested potentially showed some residual sensitivity to obstacles in their blind visual field. The final two experimental chapters went further to examine the role of perceptual information and attentional mechanisms respectively. It was found that during obstacle avoidance participants predominantly look at the movement target and rarely towards any obstacles or their moving hand. Furthermore, they tend to move their hand away from obstacles that are fixated. Finally, it was also found that a concurrent attentional task affected movement path selection in a similar way. At present it is unclear whether these perceptual and attentional effects are additive or independent of each other. Overall, these findings suggest that both conscious visual information and attentional mechanisms are crucial factors in determining movement path selection during obstacle avoidance in reaching.

Ten experiments examined the interactions between vision and audition in stimulusdriven spatial attention orienting and inhibition of return (IOR). IOR is the demonstration that subjects are slower to respond to stimuli that are presented at a previously stimulated location. In each experiment, subjects made go/no-go responses to peripheral targets but not to central targets. On every trial, a target was preceded by a sensory event, called a "cue," either in the same modality (intramodal conditions) or in a different modality (crossmodal conditions). The cue did not predict the location of the target stimulus in any experiment. In some experiments, the cue and target modalities were fixed and different. Under these conditions, response times to a visual target were shorter when it appeared at the same location as an auditory cue than when it appeared on the opposite side of fixation, particularly at short (100 ms) cue-target stimulus onset asynchronies (Experiments 1A and IB). Similarly, response times to an auditory target were shorter when it appeared at the same location as a visual cue than when it appeared at a location on the opposite side of fixation (Experiments 2A and 2B). These crossmodal effects indicate that stimulus-driven spatial attention orienting might arise from a single supramodal brain mechanism. IOR was not observed in either crossmodal experiment indicating that it might arise from modality specific mechanisms. However, for many subjects, IOR did occur between auditory cues and visual targets (Experiments 3A and 3B) and between visual cues and auditory targets (Experiment 4A and 4B) when the target could appear in the same modality as the cue on half of the trials. Finally, the crossmodal effects of stimulus-driven spatial attention orienting on auditory and visual event-related brain potentials (ERPs) were examined in the final two experiments. Auditory cues modulated the ERPs to visual targets and visual cues modulated the ERPs to auditory targets, demonstrating that the mechanisms for spatial attention orienting cannot be completely modality specific. However, these crossmodal ERP effects were very different from each other indicating that the mechanisms for spatial attention orienting cannot be completely shared. / Arts, Faculty of / Psychology, Department of / Graduate

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A study was conducted to determine if the program of perceptual-motor training outlined by D.H. Radler and Newell C. Kephart in their book, Success Through Play, would increase the perceptual-motor skills of emotionally disturbed children as measured by the Purdue Perceptual Motor Survey. Twenty children from the Portland, Oregon metropolitan area whose ages ranged from six to twelve years were included in the program. These children were grouped according to their diagnosis of withdrawn or acting-out which was received by the agency upon their referral. Three agencies participated in the study. Each child was administered the Purdue Perceptual Motor Survey before any treatment was begun and their scores were recorded on a summary sheet for comparison with the scores which they would obtain when they were retested after the experiment was completed. Then for the next nine weeks, three days a week and one half hour a day, the subjects in the experimental group received the training outlined in Success Through Play and the subjects in the control group received quiet or physical activity for an equal amount of time. At the end of nine weeks, each child was again administered the Purdue Perceptual Motor Survey and the score was recorded. The correlation of these pre- and post-test scores showed that the subjects in the experimental acting-out group improved their perceptual-motor skills significantly more than the control acting-out group; and the experimental withdrawn group improved their perceptual-motor skills significantly more than the control withdrawn group.

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How do we learn to establish associations between arbitrary visual cues (like a red light) and movements (like braking the car)? We investigated the neural correlates of visuomotor association learning in the mid-lateral cerebellum. Although cerebellum has been considered to be a motor control center involved in monitoring and correcting the motor error through supervised learning, in this thesis, we show that its role can also be extended to non-motor learning. Specifically, when primates learned to associate arbitrary visual cues with well-learned stereotypic movements, the simple spikes of the mid-lateral cerebellar Purkinje cells reported the monkey’s most recent decision’s outcome during learning. The magnitude of this reinforcement error signal changed with learning, finally disappearing when the association had been overlearned. We modeled this change in neural activity through a drift diffusion-reinforcement learning based model. The concurrent complex spikes, contrary to traditional theories, did not play the role of teaching signal, but encoded the probability of error as a function of the state of learning. They also encoded features that indicate the beginning of a trial. Inactivating the mid-lateral cerebellum significantly affected the monkey’s learning performance while it did not affect motor performance. This is because the mid-lateral cerebellum is in a loop with other cognitive processing centers of the brain including the prefrontal cortex and the basal ganglia. Finally, we verified that the features we identified in primate experiments can also be extended to humans, by studying the visuomotor association learning in humans through functional magnetic resonance imaging. In summary, through electrophysiological and causal experiments in monkeys, imaging in humans, computational models and an anatomical framework, we delineate mechanisms through which the cerebellum can be involved in reinforcement learning and specifically, learning new visuomotor associations.

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The use of mental practice to facilitate the acquisition of a motor skill was investigated. A transfer design was used to determine if the facilitation of mirror tracing performance could be attributed to learning. Following two trials on the mirror trace subjects performed either mental practice, a reading task, an attentional focus task, or massed practice. Subjects then performed trial 3. Then 52 subjects transferred to the nonpreferred hand for trials 4 and 5. The remaining subjects continued to trace with the preferred hand for trials 4 and 5. Subjects in the mental practice group traced faster than subjects in the reading task and massed practice groups, although they did not trace significantly faster than the attentional focus group. Mental practice subjects did not make significantly fewer errors than subjects in the other groups. An analysis of the transfer task indicated that the faster tracing by the mental practice group might not have been the result of learning. Females tended to trace faster and make fewer errors than males. / M.S.