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Abstract

Inverse cyclopean texture segmentation is segmentation based on monocular boundaries which are absent in the binocularly fused percept. Texture segmentation based on the monocular image does occur, even though texture segmentation is impossible in the optically fused image (Kolb & Braun, 1995). On the other hand, orientation defined, inverse cyclopean visual search is impossible (Wolfe & Franzel, 1988). The purpose of the present study was therefore to investigate these apparent contradictions in the literature.

Orientation-defined texture elements within Kolb and Braun’s stimulus occupied positions on a 20 x 20 notional grid. For Wolfe and Franzel’s stimulus, 8 texture elements were spaced evenly on a circle. The purpose of Experiments 1.1 and 3 was to determine whether the critical variable for the difference between Kolb and Braun’s and Wolfe and Franzel’s results was texture density i.e. the number of elements within the display area. We found that orientation-defined, inverse cyclopean texture segmentation was better when texture elements were dense (12 x 12) than when those elements were sparse (8 x 8) and covered the same area (Exp. 1.1 & 3). The purpose of Experiment 4 was to determine whether texture segmentation depended on orientation-defined texture boundaries that were closer together. Texture segmentation improved when the number of texture elements within the sparse grid (8 x 8) used in Experiment 3 was held constant and texture boundaries were closer together (Exp. 4). This implies that the critical difference between Kolb and Braun’s and Wolfe and Franzel’s experiments is the proximity of orientation-defined, texture boundaries.

The purpose of Experiment 2 was to investigate the possibility that, if there were an effective contrast imbalance between the two eyes, the texture boundary within an inverse cyclopean stimulus might be visible in the optically fused percept and be detected by mechanisms at a binocular stage of processing. An imbalance in sensory input from the two eyes does affect orientation-defined, inverse cyclopean texture segmentation (Exp. 2). Therefore, the purpose of Experiment 7 was to determine whether effective contrast imbalance between the two eyes was responsible for high performances for texture segmentation when texture elements were dense (Exp. 1.1 & 3) and when texture boundaries were closer together (Exp. 4). Performances for orientation-defined, inverse cyclopean texture segmentation were >80% when the balance-point was used to equalise a difference in effective contrast between the two eyes (Exp. 7.2). This implies that monocular input is available to texture segmentation mechanisms.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology
Departments:	Doctoral Theses School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses School of Health & Psychological Sciences > Optometry & Visual Sciences

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