Human visual cortical responses to specular and matte motion flows.

Tae-Eui Kam,Katja Doerschner,Daniel J Kersten,Damien J Mannion,Seong-Whan Lee

doi:10.3389/fnhum.2015.00579

Abstract

Determining the compositional properties of surfaces in the environment is an important visual capacity. One such property is specular reflectance, which encompasses the range from matte to shiny surfaces. Visual estimation of specular reflectance can be informed by characteristic motion profiles; a surface with a specular reflectance that is difficult to determine while static can be confidently disambiguated when set in motion. Here, we used fMRI to trace the sensitivity of human visual cortex to such motion cues, both with and without photometric cues to specular reflectance. Participants viewed rotating blob-like objects that were rendered as images (photometric) or dots (kinematic) with either matte-consistent or shiny-consistent specular reflectance profiles. We were unable to identify any areas in low and mid-level human visual cortex that responded preferentially to surface specular reflectance from motion. However, univariate and multivariate analyses identified several visual areas; V1, V2, V3, V3A/B, and hMT+, capable of differentiating shiny from matte surface flows. These results indicate that the machinery for extracting kinematic cues is present in human visual cortex, but the areas involved in integrating such information with the photometric cues necessary for surface specular reflectance remain unclear.

Highlights

Experiencing visual qualities, such as the glossiness of polished marble or the smoothness of silk, are an integral part of human conscious experience
We examined the response characteristics of the low and mid-level regions of human visual cortex during observation of blob-like objects with motion properties consistent with different surface attributes
The renderings were presented in four quadrants of the visual field while functional magnetic resonance imaging (fMRI) was used to measure the BOLD activity from within the posterior region of human visual cortex

Summary

Introduction

Experiencing visual qualities, such as the glossiness of polished marble or the smoothness of silk, are an integral part of human conscious experience. The automaticity with which this perceptual process occurs belies the computational difficulty that the brain is faced with in its task to extract meaningful information from the ambiguous retinal signal. The ambiguity lies in whether the pattern of light arriving at the retinae originates from variations in illumination, shape, mesoscale geometrical structure, or the material of the object. Despite this computational challenge humans can effortlessly visually sense dynamic physical properties such as viscosity, elasticity, or stiffness and optical properties such as transparency, glossiness, shininess, or roughness and discriminate between material classes. While there is a growing body of research on how the visual system extracts optical material qualities such as surface glossiness, roughness or translucency

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