Differential processing of binocular and monocular gloss cues in human visual cortex

The visual impression of an object’s surface reflectance (‘gloss’) relies on a range of visual cues, both monocular and binocular. While previous imaging work has identified processing within ventral visual areas as important for monocular cues, little is known about cortical areas involved in processing binocular cues. Here we used human functional magnetic resonance imaging (fMRI) to test for brain areas selectively involved in the processing of binocular cues. We manipulated stereoscopic information to create four conditions that differed in their disparity structure and in the impression of surface gloss that they evoked. We performed multi-voxel pattern analysis to find areas whose fMRI responses allow classes of stimuli to be distinguished based on their depth structure vs. material appearance. We show that higher dorsal areas play a role in processing binocular gloss information in addition to known ventral areas involved in material processing, with ventral area LO responding to both object shape and surface material properties. Moreover, we tested for similarities between the representation of gloss from binocular cues and monocular cues. Specifically, we tested for transfer in the decoding performance of an algorithm trained on glossy vs. matte objects defined by either binocular or by monocular cues. We found transfer effects from monocular to binocular cues in V3B/KO, suggesting a shared representation of the two cues in this area. These results indicate the involvement of mid-to-high level visual circuitry in the estimation of surface material properties, with V3B/KO potentially playing a role in integrating monocular and binocular cues.This project was supported by fellowships to A.E.W. from the Wellcome Trust (095183/Z/10/Z) and to H.B. from the Japan Society for the Promotion of Science (JSPS KAKENHI (26870911)).This is the final version of the article. It first appeared from the American Physiological Society via https://doi.org/10.1152/jn.00829.201