Brightness Induction: A Study of Correlates of Surface Brightness in Early Visual Areas

Abstract

The neural mechanisms of surface perception are surprisingly poorly understood and ongoing research both in the domain of neurophysiology with animal models and fMRI in humans has led to conflicting results. In the domain of surface brightness perception, it is debated whether surface perception depends on the interpolation of brightness in early visual areas across regions in the visual field, where that information is physically absent. We used functional Magnetic Resonance Imaging (fMRI) in human subjects to test for a possible contribution of early visual areas to the perception of surface brightness. A brightness induction paradigm was employed in which counterphase illusory brightness changes on a grey surface are induced by dynamic luminance changes in the surround. We found fMRI activity in area V2 that may be attributable to the perceived brightness modulation of the constant, grey surface. This finding suggests a role of early visual cortex in the perception of surface brightness. The data are presented within the context of related neurophysiological studies in cat and monkey, as well as other human fMRI studies. Further experiments have to be performed to conclusively demonstrate a correlate of brightness interpolation during surface perception in humans.