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Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 91-97).

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The mamalian visual system contains a limited number of receptors, which project to a limited number of cells in the visual cortex. This projection provides a point-to-point representation of the retinal stimulation onto the visual cortex. Data reported by Marshall and Talbot (1942) suggest that contours in the environment are represented on the visual cortex by a process involving the summation of neural activity around the area receiving the retinal projection. Such anatomical and physiological evidence suggests a simple mechanism by which forms are perceived; the perception of form should correspond to retinal stimulation by form. [...]

Memory for visual patterns was examined in 131 patients with unilateral temporal- or frontal-lobe excisions and 32 normal control subjects. A deficit in short-term memory for matrices of increasing complexity was exhibited by the right frontal-lobe group. Right temporal lobectomy impaired cued recall of visually homogeneous matrices at each of four serial positions. On the delayed recognition of complex visual scenes, right temporal lobectomy decreased identification of changes in figurative detail and spatial composition, whereas right hippocampectomy impaired identification of changes in spatial location. The interplay between verbal and pictorial codes in memory was also investigated using related word-design pairs. Right or left temporal lobectomy affected the number of designs recalled but only the right temporal-lobe group produced designs of poor quality. When cued with the words, the left temporal-lobe group produced fewer designs than the control subjects, demonstrating a reduced ability to retrieve pictorial information through verbal labels.

According to Feature Integration Theory (Treisman & Gelade, 1980), search for a target defined by features on two different dimensions (e.g. green horizontal target among red horizontal and green vertical distractors) is conducted via serial attentive search of all items in the array. Results presented in this thesis clearly demonstrate that conjunction search is not conducted as a serial self-terminating search, and suggest that subjects selectively search a single feature set. Strong support is also provided for the role of local grouping processes in visual conjunction search. This includes evidence demonstrating: (1) that local context is an important factor in directing search toward the target, and (2) that groups of spatially adjacent homogeneous elements can be processed in parallel. These results point to the importance of spatial layout of target and distractor elements. More recent theories (e.g. Cave & Wolfe, 1990) will have to be amended in order to account for these data.

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