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Laysa Hedjar, Arthur Shapiro; Thin luminance gaps can eliminate contrast-mediated perceptual asynchronies. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4215.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast asynchrony (CA) configurations can separate the visual response to color from the visual response to color contrast (Shapiro, 2008). Recent variations of the basic CA configuration have demonstrated powerful spatial interactions that may be useful for the assessment of visual function. Here we empirically investigate these spatial interactions and attempt to account for the results with a model based on difference of gaussian (DoG) spatial filters.
The stimulus consisted of two identical bars (.5x1.0 deg) each modulating in luminance at 2 Hz (for demo see: illusionoftheyear.com/2016/06/remote-controls). One bar was placed on a bright field; the other on a dark field. The bars appear to modulate in antiphase--a perceptual response to the contrast between the bars and their surrounds, not to the luminance modulation of the bars. The asynchrony is maintained when bright rectangular flankers (.5x1.0 deg) are placed adjacent to the bar on the dark field, and dark flankers are placed adjacent to the bar on the bright field.We parametrically manipulated the length of the flankers and the width of the gap between the flankers and the modulating bars. Observers viewed the conditions in random order (20x each condition) and were asked whether the bars appear in-phase or antiphase. The observers (n=5) were college-aged with normal or corrected visual acuity.
The results are plotted as psychometric functions: number of trials perceived as asynchronous vs. distance between bars and flankers (gap). When the flankers are the same height as the bars and the gap is zero (i.e., the bars are adjacent to flankers) or greater than 12’, observers perceive antiphase modulation. However, when the gap is between 1’ and 12’, observers perceive in-phase modulation. When the flankers are longer than the modulating bars, the effect is reversed: in-phase appearance occurs for gaps of 0 and antiphase appearance for larger gaps. We model the results with a bank of contrast-driven DoG filters.
The asynchronous appearance switches when the gap is between 1’ and 12’. The results suggest an interaction between two spatial contrast responses each with different temporal phases. A DoG model can capture most, but not all, of the results. The failure to account for all results suggests the possibility of higher-order contextual segmentation.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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