Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2001. / Includes bibliographical references.

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2001. / Includes bibliographical references.

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2003. / Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 111-122).

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2002. / Includes bibliographical references.

Thesis (M.A.)--York University, 2002. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 63-66). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71617.

The purpose of the current study is to understand the relationship between the volume of the posterior cerebellar hemispheres and cross-modality divided attention in ASD and control participants. Abnormalities in shifting, orienting, and selective attention are well reported in ASD, but few studies have examined divided attention. Furthermore, there is evidence of volumetric reduction of the posterior cerebellum in ASD. However, few studies have examined the relationship between the posterior cerebellum and behavioral performance. The current study addresses this gap in the literature through structural MRI and a neuropsychological attention task. It is hypothesized that the ASD group will have impaired divided attention abilities compared to the control group. Furthermore, within the ASD group, reduced posterior cerebellar volume is expected to be associated with impaired divided attention. The study will use multiple regression analyses. As ASD is a neurodevelopmental disability with considerable heterogeneity and unknown etiology, the current study seeks to contribute to the understanding of neural and behavioral markers of ASD. / text

Perceptual grouping plays an indispensable role on attention distribution. An example of this interaction is the impaired visual search performance when the target overlaps with a task-irrelevant salient distractor organized to a snake-like configuration by collinear bars, and when the collinear distractor is long enough (Jingling & Tseng, 2013). This phenomenon is puzzling because it is opposite to our understanding of attention capture which predicts search facilitation instead of impairment. As an attempt to fully understand the interaction between perceptual grouping and attention, the current research probed the possible neural stage of this collinear search impairment effect. In Study 1, the distractor column of the search display was split into two eyes: one eye saw a distractor with varied length (= 1, 5, or 9 bars) while the other eye saw the rest of the distractor column. When both eyes were properly fused, observers saw a search display containing a 9-bar distractor. Observers were asked to identify the orientation of a target gap that could be overlapping or non-overlapping with the distractor. It was found that search impairment was dominated by monocular collinear distractor length. In Study 2, a 9-bar distractor was shown to one eye of observers and strong flashing color patches were shown to the other eye (Continuous Flash Suppression) such that part of the distractor was suppressed from observers’ awareness. It was found that invisible collinear distractor parts enhanced search impairment, suggesting awareness of the distractor is not necessary for the effect. Results from both studies converge to suggest that the effect of collinear grouping on attention is likely to be at early visual sites like V1 where monocular information but not awareness is processed. It highlights the need to incorporate perceptual grouping into current salience-based attention models. / published_or_final_version / Psychology / Master / Master of Philosophy

Visual perception can be improved by the intentional allocation of attention to specific visual components. This “top-down” attention can improve perception of specific locations in space, or of specific visual features at all locations in space. Both spatial and feature attention are thought to involve the feedback of attention signals from higher cortical areas to visual cortex, where it modulates the firing rates of specific sensory neurons. However, the mechanisms that determine how top-down attention signals modulate the firing rates of visual neurons are not fully understood. Recently, a sensory mechanism called normalization has been implicated in mediating neuronal modulations by attention. Normalization is a form of gain control that adjusts the dynamic range of neuronal responses, particularly when more than one stimulus lies within a neuron's receptive field. Models of attention propose that this sensory mechanism affects how attention signals modulate the firing rates of sensory neurons, but it remains unclear exactly how normalization is related to the different forms of top-down attention. Here we use single unit electrophysiological recordings from the middle temporal area (MT) of rhesus monkeys to measure the firing rates of sensory neurons. We ask the monkeys to perform a behavioral task that directs their attention to a particular location or feature, allowing us to independently measure modulations to firing rates due to normalization, spatial attention, or feature attention. We report that variations in the strength of normalization across neurons can be explained by an extension of conventional normalization: tuned normalization. Modulation by spatial attention depends greatly on the extent to which the normalization of a neuron is tuned, explaining a neuron-by-neuron correlation between spatial attention and normalization modulation strengths. Tuned normalization also explains a pronounced asymmetry in spatial attention modulations, in which neurons are more modulated by attention to their preferred, versus their non-preferred, stimulus. However, feature attention differs from spatial attention in its relationship to the normalization mechanism. We conclude that while spatial and feature attention appear to be mediated by a common top-down attention mechanism, they are differently influenced by the sensory mechanism of normalization.

published_or_final_version / abstract / toc / Psychiatry / Master / Master of Philosophy