Binocular contrast perception of gratings, noise, and natural images

Abstract

The visual system is tasked with combining the two eye’s views into a single percept of the world. To understand the principles that underlie this combination, dichoptic stimuli (stimuli that have different levels of luminance and/or contrast in the two eyes) can be used to probe how each eye’s input contributes to the ultimate binocular percept. For example, contrast perception of simple dichoptic stimuli, such as sine wave gratings, is well-predicted as a weighted combination of the two eyes inputs typically biased towards the eye seeing higher contrast. We aimed to examine contrast perception of more complex dichoptic stimuli to determine how higher-order visual properties may influence the binocular percept. Using a perceptual matching task in which participants adjusted one stimulus (which was non-dichoptic) to match the perceived contrast of another stimulus (which was dichoptic), we examined the perceived contrast of three classes of stimuli: gratings, 1/f noise, and natural image patches. In addition to finding the closest perceptual match, we also asked participants to report on whether and how the two stimuli differed in appearance. We found that: 1) Spatial variation in the stimuli modulated binocular contrast perception; however, the effect depended on the stimulus type. Specifically, spatial manipulations that affected the perceptual matches for gratings (i.e., increasing or decreasing the contrast of the surrounding area in either eye) did not have a systematic effect on the matches for the noise and natural images. 2) Across all stimulus types, however, spatial manipulations did affect the proportion of trials in which participants reported finding an “exact match”. These results suggest that spatial frequency interactions and higher-level inferences can modulate both the interocular weighting and the perceptual interpretation during binocular combination.