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

Hua-Chun Sun,Hiroshi Ban,Massimiliano Di Luca,Andrew E Welchman,Alexander Muryy,Roland W Fleming

doi:10.1152/jn.00829.2015

Abstract

The visual impression of an object's surface reflectance (“gloss”) relies on a range of visual cues, both monocular and binocular. Whereas 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 MRI (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 multivoxel 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 lateral occipital 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 dorsal visual area V3B/kinetic occipital (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.

Highlights

SURFACE GLOSS PROVIDES IMPORTANT information about the characteristics of visual objects: for instance, shiny metal objects are usually manufactured recently and have better conductance than rusty metal, whereas fresh apples have glossier skin than rotten ones
We tested for responses related to surface gloss, contrasting the mirror and anti-mirror conditions [both perceived as glossy (Fig. 2), and their averaged, overall disparity is the same as in the painted condition] against the painted object
We contrasted the painted and flat conditions, which provides the maximal change in 3D shape, whereas both are interpreted as not evoking a strong impression of gloss (Fig. 2)

Summary

Introduction

SURFACE GLOSS PROVIDES IMPORTANT information about the characteristics of visual objects: for instance, shiny metal objects are usually manufactured recently and have better conductance than rusty metal, whereas fresh apples have glossier skin than rotten ones. A number of investigators have studied the neural basis of gloss computations by manipulating the specular and diffuse surface-reflectance properties of objects (Kentridge et al 2012; Nishio et al 2012, 2014; Okazawa et al 2012; Sun et al 2015; Wada et al 2014). Human studies suggested that specular highlight cues to gloss are primarily processed in the ventral processing stream: V4, ventral occipital 1/2 area, lateral occipital (LO) area, collateral sulcus, and posterior fusiform sulcus (pFs) (Sun et al 2015; Wada et al 2014). Work characterizing the properties of binocular reflections has shown that the disparities evoked by such stimuli often differ substantially from the disparities evoked when viewing matte objects: disparity gradients are larger, and there can be large, vertical offsets between corresponding image features (Muryy et al 2013, 2014)

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