Abstract
A new illusion demonstrates the difference between how achromatic and chromatic neural signals from the two eyes are combined binocularly. Two spatially homogeneous circles were presented separately to each eye at corresponding retinal locations. Each eyes circle alternated over time between the same two lights (either between 2 equiluminant or 2 achromatic lights). Temporal oscillation in the two eyes was always at the same frequency but opposite in phase. Square-wave frequencies ranged from 1.5 to 9.4 Hz. Equiluminant chromaticities oscillated around equal-energy-spectrum (EES) white along one cardinal color direction (L/(L+M) or S/(L+M)) or along a diagonal direction that varied both cardinal directions simultaneously. Surprisingly, equiluminant modulation often resulted in very slow perceptual color alternation, with one or the other chromaticity remaining continuously visible for several seconds or longer. Oscillation along the achromatic axis, however, never resulted in slow perceptual alternation. Known neurophysiology of binocular integration of chromatic versus achromatic stimuli may explain the properties of the illusion. Peirce et al. (2008) recorded from binocular neurons in macaque V1 while presenting to each eye a spatially homogeneous field that alternated between two equiluminant chromaticities, or between two achromatic luminances. The color-tuning of the two monocular receptive fields of binocular neurons was well matched for neurons preferring chromatic stimulation but poorly matched for neurons preferring achromatic stimulation. In our illusion, stable periods of perceptual dominance of only one or the other chromaticity can occur because, when switching chromaticities between eyes, the response from binocular neurons preferring chromatic stimulation will be fairly stable. In contrast, binocular neurons preferring achromatic stimulation will have an unstable response and therefore cannot support a stable percept.
Meeting abstract presented at VSS 2014