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Abstract

Slowly alternating, instead of rapidly flickering, fused colors are perceived when two equiluminant but chromatically rivalrous stimuli (e.g. one “pink” and one “blue-green” disc) are presented separately to each eye and then swapped interocularly several times a second. This is a visual illusion induced by chromatic interocular-switch rivalry (CISR) (Christiasen, D’Antona & Shevell, 2014). Since CISR creates steady-state ambiguous neural representations of color beyond the level of the eye, it provides a novel approach to studying how the visual system interprets color in mid-level vision. Experiment 1 investigated CISR at several different temporal frequencies to determine the frequency range over which relatively long-lasting color percepts are seen. The results showed that, in general, 3.13 Hz, 3.75 Hz and 4.69 Hz CISR resulted in stable long-duration color percepts. Experiment 2 investigated whether grouping contributes to the long-lasting color percepts during CISR. This question was tested using two different paradigms with either two or four independent CISR stimuli. The results showed that grouping contributes to the resolution of the objects’ colors. Experiments 3, 4 and 5 investigated what feature-based object properties contribute to grouping in the resolution of CISR. The features tested included synchronized temporal phase at a common frequency (experiment 3), identical temporal frequencies (experiment 4), and equal stereoscopic disparity (experiment 5). The results did not show evidence that grouping was affected by these object features. Experiment 6 investigated whether ambiguity-based features affect grouping of two separate objects presented with CISR. Coherent ambiguity was tested with two CISR stimuli, compared to one object with CISR and the other object non-rivalrous (so no ambiguity). The results showed that the resolution of CISR by grouping depends on coherent ambiguity of the two objects. Experiment 7 investigated chromatic adaptation during CISR to test whether a predominant color percept is related to the state of chromatic adaptation. The results showed that the color percept during CISR affected chromatic adaptation for two of the three observers. Taken together, these experiments show that perceptual resolution of chromatic neural ambiguity, created with CISR, depends on object grouping. Therefore, the results demonstrate the importance of grouping for resolving ambiguous chromatic neural representations.

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