Contrast Gain Control in Glass Pattern Perception
Date Issued
2015
Date
2015
Author(s)
Cho, Pao-Chou
Abstract
Glass patterns (Glass, 1969) consist of randomly distributed dot pairs and their orientation is determined by certain mathematical transformations. In this study, a new pattern with a group of randomly distributed triple dots (tripoles) was used. Each tripole comprises an “anchor dot,” which is close to the center of the pattern, and two side dots. The distance between the anchor dot and each side dot as well as between the two side dots is equal. By manipulating the luminance contrast of each dot in the tripoles, if in the tripoles, the visual system groups the anchor dot with one of the two side dots, and the Glass pattern will be perceived to spiral in one direction (and vice versa). Meanwhile, the other side dot, which is not being grouped, would systematically influences the process of the grouped dots. The purpose of this study is to see how the variation of luminance contrast of intra-tripoles affects the local grouping and, then, the global perception. The anchor-contrast was either -20 or -10.46dB, and the contrast of side dots ranged from -29.54 to -0.92dB. The study involved a forced-choice paradigm. The probability of an observer’s categorization of a tripole Glass pattern as counter-clockwise or clockwise pattern was measured. The result showed that as the contrast of a side dot increased, the probability of it being grouped with the anchor dot increased initially, and then, the probability dropped as the contrast of side dot is greatly different from the anchor dot. Furthermore, the peak of response curve was not at where the grouped dots are of similar contrast, but where they are modulated by the contrast of the dot, which was not being grouped. As the contrast of the side dot, which was not being grouped to the anchor dot, increased, the peaks moved toward where the grouped side dots were of high contrast. The result could be fitted with a divisive inhibition model, which was the response of each mechanism resulting from an output of the linear operator divided by the sum of relevant channels. Meanwhile, the shift of the response curves could be accounted for by the inhibition input, which suggests that the contrast processing of Glass pattern is mediated by a contrast gain-control mechanism.
Subjects
luminance contrast
Glass patterns
form
categorization
shape
Type
thesis
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