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Arthur Shapiro, Venice Cowardin, Angel Wen; Contextual effects and the contrast asynchrony: a new phenomenon shows a cancellation of contrast responses. Journal of Vision 2016;16(12):820. doi: 10.1167/16.12.820.
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© ARVO (1962-2015); The Authors (2016-present)
The visual system has separable visual encoding for luminance and for contrast modulation (Shapiro, 2008); the two dimensions can be represented with a luminance contrast vs. luminance plane. Here we use a contrast asynchrony paradigm to explore contextual effects on luminance contrast modulation: two identical rectangular bars (0.5x1.0 deg) have luminance levels that modulate at 2 Hz; when one bar is placed on a bright field and the other bar on a dark field, observers perceive the bars modulating in antiphase with each other and yet becoming light and dark at the same time. The antiphase perception corresponds to the change in contrast between the bars and their surrounds (a change along the contrast axis of the plane); the in-phase perception corresponds to the luminance modulation (a change along the luminance axis of the plane). We examine spatial interaction by adding bright rectangular (0.5x1.0 deg) flankers on both sides of the dark-field bar and dark flankers on both sides of the bright-field bar. Remarkably, flankers produce an in-phase appearance when separated from the bars by between 1' and 12' of visual angle, and produce antiphase appearance when they directly adjoin the bars or are separated by more than 12'. To estimate the dimensions of the spatial interaction, we parametrically adjust the amplitude of modulation and the height of the flankers. We model the results in terms of spatial filters. We show that modulation produces two contrast phase responses: with distant flankers, the modulating rectangle against the dark background is in Phase A, and the rectangle against the white background is in Phase B; with adjoining flankers, the contrast phase reverses. The in-phase appearance for gaps between 1' and 12' seems to represent a perceptual cancellation of the two contrast responses.
Meeting abstract presented at VSS 2016
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