Dichoptic presentation of the contrast asynchrony suggests a retinal locus for the contrast response

Abstract

The contrast asynchrony is a stimulus configuration that illustrates that the visual system has separable responses to color and color contrast (Shapiro et al, 2004; Shapiro 2008). The basic version of the stimulus consists of two disks whose luminance modulates sinusoidally in time at 1 Hz; one disk is surrounded by a dark ring, and the other disk by a bright ring. The luminance of the disks modulates in phase with each other, and the contrast of the disks relative to their surrounding ring modulates in antiphase. When viewing the contrast asynchrony at 1 Hz, observers perceive the disks to modulate in antiphase relative to each other (consistent with the processing of contrast information), but to get light and dark at the same time (consistent with the processing of luminance information). Here we present the results of experiments in which observers viewed the contrast asynchrony dichoptically. We report that no asynchrony is perceived when one eye is presented with modulating disks, and the other eye is presented with the black and white surround rings, nor is an asynchrony perceived in gradient versions of the contrast asynchrony (like Shapiro et al, 2005). We compare these results to dichoptically presented brightness settings. Consistent with what has been reported elsewhere in the literature, black and white surround rings presented to one eye induce brightness changes in disks presented to the other eye. When we present demonstrations that compare the temporal response of the contrast asynchrony to the temporal response of dichoptic brightness induction, the contrast asynchrony occurs at rates much faster than brightness induction (as expected). The results give further evidence that the contrast response can be separated from brightness induction. The results are consistent with a retinal locus of the contrast asynchrony, whereas aspects of brightness induction may occur cortically. Background Shapiro et al (2004, 2005, 2008) presented two physically identical disks, one surrounded by a dark ring and the other by a light ring. The luminance levels of both disks are modulated simultaneously at 1 Hz. The luminance of the disks modulates in phase, while the contrast between the disks and the rings modulates in antiphase. Contrast asynchrony The stimulus leads to the paradoxical perception that the disks modulate in antiphase yet also get light and dark at the same time. The appearance The contrast asynchrony shows separable responses to color and to color contrast (Shapiro, 2008). What are the origins of the separate responses? There are three possible skeletal models: The Question Can the luminance contrast response be perceived dichoptically? Methods and Equipment Simple Contrast Asynchrony Monocular contrast Binocular contrast Contrast Asynchrony against gradient backgrounds