Advancements in movement restoration have accelerated in recent years while the restoration of somatosensation has progressed relatively slowly. This dissertation attempts to partially correct this oversight by developing an electrotactile feedback system that might be used to restore the sense of touch.Initially, the perceptual parameters of the skin regions likely to be used as a source of tactile information (the fingertip) and as a destination for electrotactile feedback (the back of the neck) were evaluated. The perceptual parameters of tactile threshold sensitivity, spatial acuity, and gain scaling were collected from subjects for both regions of skin. These same parameters were also gathered in response to electrotactile stimulation of the neck. The threshold sensitivity and spatial acuity of the fingertip was found to be far superior to that on the back of the neck, yet the mechanical perceptual gain scaling parameters of the neck were similar to that of the finger tip. Yet, the psychometric functions for electrical stimulation on the neck differed markedly in gain sensitivity from that of mechanical stimulation. A mapping function between the two modalities was then calculated based upon the tactile and electrotacile characterization data that was collected.An electrotactile feedback system was then developed based upon the calculated mapping function, allowing conversion of force applied to an artificial sensor on the fingertip to a perceptually equivalent electrical stimulus on the neck. The system proved to be quite effective: Subjects were able to effectively evaluate electrical stimulus that was derived from application of force to the sensor on the fingertip. The perceptual gain scaling for the feedback system matched that of natural mechanical stimulation.A grip force matching task was evaluated in test subjects under three conditions: a) normal tactile sensation, b) anesthesia of the fingers, and c) anesthesia of the fingers with restored tactile information via the electrotactile feedback system. The relative loss in grip-force matching ability when tactile feedback was abolished by local anesthetic was mild, indicating a strong ability for individuals to generate target force levels using other forms of feedback. Electrotactile feedback, therefore, offered only modest improvement when deployed in the anesthetized hand.

Current models of face perception suggest independent processing of identity and expression, though this distinction is still unclear. Using converging methods of psychophysics and functional magnetic resonance imaging (fMRI) in healthy and patient populations we assessed the relationship between these two perceptual processes. First, using perceptual aftereffects, we explored the neural representations underlying identity and expression. The expression aftereffect only partially transferred across different identities, suggesting adaptation within identity-invariant and identity-dependent expression representations. Contrarily, the identity aftereffect fully transferred across different expressions. This asymmetry cannot be explained through low-level adaptation. The identity-dependent component of the expression aftereffect relies on adaptation to a coherent expression, not low-level features, in the adapting face. Thus adaptation generating the expression aftereffect must occur within high-level representations of facial expression. Second, using fMRI adaptation, we examined identity and expression sensitivity in healthy controls. The fusiform face area and posterior superior temporal sulcus showed sensitivity for both identity and expression changes. Independent sensitivity for identity and expression changes was observed in the precuneus and middle superior temporal sulcus respectively. Finally, we explored identity and expression perception in a neuropsychological population. Selective identity impairments were associated with inferior occipitotemporal damage, not necessarily affecting the occipital or fusiform face areas. Impaired expression perception was associated with superior temporal sulcus damage, and also with deficits in the integration of identity and expression. In summary, psychophysics, neuroimaging and neuropsychological methods all provide converging evidence for the independent processing of identity and expression within the face network. However, these same methods also supply converging evidence for a partial dependence of these two perceptual processes: in the expression aftereffect, the functional sensitivities of the FFA and pSTS, and identity deficits observed in a patient with primarily impaired expression perception and a spared inferotemporal cortex. Thus, future models of face perception must incorporate representations or regions which independently process identity or expression as well as those which are involved in the perception of both identity and expression.

No description available.

The simultaneous application of interlaced innocuous warm and cool stimuli can elicit sensations of burning heat (the Thermal Grill Illusion, TGI). The TGI is thought to reflect changes in the central interactions between somatosensory sub-modalities (i.e. cold-inhibition of pain). Previous studies used multiple alternating warm and cool bars to elicit a TGI. The primary objective of this study was to evaluate the effects of altering the placements of warm and cool grill elements on the intensities of perceived pain and unpleasantness in 26 male subjects. Arranging the thermal grill elements in a warm flanking cool (WCW) pattern evoked significantly higher intensities of pain and unpleasantness than a cool flanking warm (CWC) pattern and a uniform warm stimulus. Conversely, CWC did not elicit significantly different intensities of perceived pain and unpleasantness than a uniform cool stimulus. This finding may reflect differences in the level of activation of central neurons.

The simultaneous application of interlaced innocuous warm and cool stimuli can elicit sensations of burning heat (the Thermal Grill Illusion, TGI). The TGI is thought to reflect changes in the central interactions between somatosensory sub-modalities (i.e. cold-inhibition of pain). Previous studies used multiple alternating warm and cool bars to elicit a TGI. The primary objective of this study was to evaluate the effects of altering the placements of warm and cool grill elements on the intensities of perceived pain and unpleasantness in 26 male subjects. Arranging the thermal grill elements in a warm flanking cool (WCW) pattern evoked significantly higher intensities of pain and unpleasantness than a cool flanking warm (CWC) pattern and a uniform warm stimulus. Conversely, CWC did not elicit significantly different intensities of perceived pain and unpleasantness than a uniform cool stimulus. This finding may reflect differences in the level of activation of central neurons.

Maximum voluntary forces and psychophysically acceptable forces are often used to set force guidelines for exertions as a means to protect against overexertion injuries in the workplace. The focus of this dissertation was the exploration of the roles of whole body balance, shoe-floor friction and joint strength in limiting the capacity of a person to produce maximum voluntary hand forces and psychophysically acceptable hand forces. The underlying goal was to advance knowledge regarding how physical exertion capacity is biomechanically governed, then to use this information to develop models to predict capability based on these governing principles. The hypothesis underscoring this work was that maximum voluntary hand force capability is governed by whole body balance, shoe-floor friction and joint strength; and consequently, psychophysically acceptable forces would be chosen proportionally to this maximum voluntary force capability, where the magnitude of the proportionality was dependent on the limiting factor, or ‘weakest link’. To investigate this hypothesis, both experimental and mathematical modeling paradigms were used. Initially, an experimental study was used to investigate how biomechanical factors governed maximum hand force capability across a range of exertions. It revealed that each governing factor differentially limited maximum force capability. Moreover, this study identified how foot placement, handle height, distance from the handle, friction, and body posture all influence the underlying biomechanical weakest link, and ultimately force producing capability. Data gathered in the experimental study was next used to evaluate a mathematical model that was developed to predict maximum force capability, given information on posture and direction of force application. In addition, the model also predicted population variability in maximum capacity based on the inclusion of a novel approach to probabilistically represent population variability. The evaluation demonstrated that the model underestimated maximum hand force capability compared to measured hand forces by approximately 18, 26, and 41% during medial, pulling and downward exertions respectively. However, it appeared that the ‘weakest link’ principle for predicting maximum force capacity was plausible, as evidenced by significant rank ordered correlations between the measured and predicted hand forces. Further research investigated if psychophysically acceptable forces were selected as a proportion of task specific maximum voluntary force capability, where the proportionality was related to the biomechanical weakest link. Using an experimental design, psychophysically acceptable forces and corresponding maximum forces were measured. Participants chose psychophysically acceptable forces that were 4/5ths of their task specific maximum voluntary force capability when capability was limited by balance. Additionally, they choose psychophysically acceptable forces that were 2/3rds of their maximum voluntary force capability when capability was limited by joint strength. The identification and confirmation of a weakest link proportionality principle represents an important contribution to the field of occupational biomechanics. The weakest link proportionality principle was integrated into the model to allow prediction of: maximum voluntary hand force capability, the limiting factor, and psychophysically acceptable hand force capability. The updated model underestimated empirically measured psychophysically acceptable forces by 24% and 43% during downward and pulling exertions respectively. However, the original model underestimated the maximum hand force capacity by 23% and 34% during the same exertions, without the proportional relationships. This underestimation may be a result of the underlying assumption that joint strength is independent, resulting in an underestimation of maximum joint strength capacity and a corresponding underestimation of maximum hand force capacity. The underestimation may also be due to differences in strength capacities between the participants tested during this thesis compared to those tested in past research used to determine the maximum strength indices reported in the literature. This body of work supported the hypothesis that psychophysically acceptable forces are selected as a proportion of the maximum voluntary hand force, where the proportionality depends on the underlying biomechanical weakest link. The model is a promising first step towards predicting maximum and psychophysically acceptable occupational force threshold limits.

A series of experiments is described which uses a perceptual matching approach to study the effect of exogenous visual cues on perception of static and dynamic stimuli. Analogous experiments were carried out for orientation judgments of rotated Gabor patches and for direction of motion of coherent dot motion. Response time effects of cuing were found in all conditions. Cuing was found to improve accuracy of orientation judgments, while the effects on motion judgments were less reliable. Cuing was found to have substantially larger effects on quality of orientation judgments at low contrast levels. Other analyses performed found sequential trial effects and qualitatively different effects of canonical directions on orientation and motion judgments.

Current models of face perception suggest independent processing of identity and expression, though this distinction is still unclear. Using converging methods of psychophysics and functional magnetic resonance imaging (fMRI) in healthy and patient populations we assessed the relationship between these two perceptual processes. First, using perceptual aftereffects, we explored the neural representations underlying identity and expression. The expression aftereffect only partially transferred across different identities, suggesting adaptation within identity-invariant and identity-dependent expression representations. Contrarily, the identity aftereffect fully transferred across different expressions. This asymmetry cannot be explained through low-level adaptation. The identity-dependent component of the expression aftereffect relies on adaptation to a coherent expression, not low-level features, in the adapting face. Thus adaptation generating the expression aftereffect must occur within high-level representations of facial expression. Second, using fMRI adaptation, we examined identity and expression sensitivity in healthy controls. The fusiform face area and posterior superior temporal sulcus showed sensitivity for both identity and expression changes. Independent sensitivity for identity and expression changes was observed in the precuneus and middle superior temporal sulcus respectively. Finally, we explored identity and expression perception in a neuropsychological population. Selective identity impairments were associated with inferior occipitotemporal damage, not necessarily affecting the occipital or fusiform face areas. Impaired expression perception was associated with superior temporal sulcus damage, and also with deficits in the integration of identity and expression. In summary, psychophysics, neuroimaging and neuropsychological methods all provide converging evidence for the independent processing of identity and expression within the face network. However, these same methods also supply converging evidence for a partial dependence of these two perceptual processes: in the expression aftereffect, the functional sensitivities of the FFA and pSTS, and identity deficits observed in a patient with primarily impaired expression perception and a spared inferotemporal cortex. Thus, future models of face perception must incorporate representations or regions which independently process identity or expression as well as those which are involved in the perception of both identity and expression.

Thesis (M.A.)--York University, 2006. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 89-93). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR19699

Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaf 130).