Perceptual resolution of color for multiple chromatically ambiguous objects

Abstract

In a classic study, Kovács et al. [Proc. Natl. Acad. Sci. USA 93, 15508 (1996)] used an array of many disks presented dichoptically with half of the disks in one eye “red” and the other half “green;” disk chromaticities in the fellow eye were reversed, resulting in binocular color rivalry for every disk, thus creating color ambiguity. Surprisingly, the binocularly fused percept sometimes was all disks of the same color (red or green), which showed that perceptual resolution of the many ambiguous neural representations did not rely completely on monocular dominance or on independent resolution for each disk. The present study replicates and expands on the original with the aim to isolate binocularly driven neural mechanisms of perceptual resolution without contamination from monocular dominance. Observers viewed a color-rivalrous array with 16 disks presented either steadily to each eye, as in Kovács et al., or with chromatic interocular-switch rivalry (CISR), which swaps the two images between the eyes every 133 ms. The total proportion of viewing time when the 16 disks were perceived to be all red or all green was measured. For three observers, the disks all appeared the same color more often with CISR than with steady rivalrous presentation, suggesting that monocular dominance interferes with grouped perceptual resolution of ambiguous stimuli in the Kovács paradigm. This conclusion was supported by an additional condition using CISR, but with every disk the same color in one eye at each instant (e.g., all “red” disks in one eye and all “green” in the other). This condition was never significantly different from the original CISR condition, as expected if CISR reveals only binocularly mediated perceptual resolution of the disks’ color, irrespective of monocular neural representations. In conclusion, chromatically tuned binocularly driven neurons account for perceptual resolution of CISR.

Perceptual resolution of ambiguous neural representations for form and chromaticity

“…Previous work has shown that multiple chromatically rivalrous discs viewed simultaneously and presented with ISR all appear the same color far more often than chance (Slezak & Shevell, 2018). This implies grouping among the discs; that is, the color of each rivalrous disc in view is not determined independently of the others.…”

“…In ISR, luminance-defined form also has been found to produce percepts consistent with dominance of monocularly driven neural representations (Lee & Blake, 1999; Denison & Silver, 2012; Brascamp, Sohn, Lee, & Blake, 2013). Equiluminant chromatic stimuli presented in ISR, however, give percepts accounted for by competition between binocularly driven neurons and minimize or eliminate the monocular dominance found with SBR (Slezak & Shevell, 2018). The current study did not find evidence for monocular cues influencing grouping during chromatic ISR, as there never was a significant difference between conventional and patchwork rivalrous stimuli (Experiment 1).…”

“…This method, when used with equiluminant rivalrous chromaticities, produces slowly alternating color percepts lasting about 2 s on average (that is, longer than six or more chromaticity swaps in each eye). These sustained color percepts can be accounted for by competition between binocularly driven neurons without any monocular rivalry mechanism (Christiansen et al, 2017; Slezak & Shevell, 2018). Equiluminant chromatic ISR causes slow alternating color percepts without adding higher frequency on-off flicker, as required for luminance-defined switch rivalry (Logothetis et al, 1996, Lee & Blake, 1999; Denison & Silver, 2012).…”

“…Apparatus and stimulus arrangements. (a) A mirror haploscope display (as in Slezak & Shevell, 2018). The black rectangle represents the CRT monitor, the solid gray lines represent front-surface mirrors, and the dashed lines indicate the light paths.…”

“…While grouping of ambiguous visual representations (of chromaticity or form) is well known (e.g., Kovács, Papathomas, Yang, & Fehér, 1996; Ngo, Miller, Liu, & Pettigrew, 2000; Slezak & Shevell, 2018), fundamental questions remain about grouping with multiple stimulus features. Must neural representations have all features matching in order to be grouped?…”