No Functional Magnetic Resonance Imaging Evidence for Brightness and Color Filling-In In Early Human Visual Cortex

Abstract

The brightness and color of a surface depends on its contrast with nearby surfaces. For example, a gray surface can appear very light when surrounded by a black surface or dark when surrounded by a white surface. Some theories suggest that perceived surface brightness and color is represented explicitly by neural signals in cortical visual field maps; these neural signals are not initiated by the stimulus itself but rather by the contrast signals at the borders. Here, we use functional magnetic resonance imaging (fMRI) to search for such neural "filling-in" signals. Although we find the usual strong relationship between local contrast and fMRI response, when perceived brightness or color changes are induced by modulating a surrounding field, rather than the surface itself, we find there is no corresponding local modulation in primary visual cortex or other nearby retinotopic maps. Moreover, when we model the obtained fMRI responses, we find strong evidence for contributions of both local and long-range edge responses. We argue that such extended edge responses may be caused by neurons previously identified in neurophysiological studies as being brightness responsive, a characterization that may therefore need to be revised. We conclude that the visual field maps of human V1 and V2 do not contain filled-in, topographical representations of surface brightness and color.

Neural Correlates of Color-Selective Metacontrast in Human Early Retinotopic Areas

“…The extent of spread was comparable to that found in V1 and V2 for responses to luminance and color edges (Cornelissen et al 2006). The spread would thus not necessarily imply suppression of maskrelated activity.…”

Dynamic brightness induction in V1: Analyzing simulated and empirically acquired fMRI data in a “common brain space” framework

“…The most convincing evidence comes from neurophysiological recordings in the cat (Rossi and Paradiso, 1999;Rossi et al, 1996), which showed that in about 10% of area 17 neurons with their receptive fields (RFs) placed within the probing region, activity was modulated in anti-phase to inducer luminance (i.e., activity correlated to perceived brightness changes). Two human studies using functional magnetic resonance imaging (fMRI) have reported data that appear in agreement with the neurophysiological data (Pereverzeva and Murray, 2008; van de Ven et al, in preparation), whereas a third fMRI study (Cornelissen et al, 2006) did not observe a brightness induction correlate in early visual cortex.The model we propose contains three main parts (Fig. 1).…”

Early Human Visual Cortex Encodes Surface Brightness Induced by Dynamic Context

“…Peters, Jans, van de Ven, De Weerd, & Goebel, 2010;Roe et al, 2005;Ramsden et al, 2001), although this effect may be smaller compared with V2, and our paradigm or stimulus may not have been sensitive enough to pick up the effect in V1. Some fMRI studies, in fact, did not find a brightness correlate in neither V1 nor extrastriate cortex using brightness induction (Cornelissen et al, 2006;Perna et al, 2005) as experimental paradigms.…”

“…Antiphase signals attenuate each other when they spread into each otherʼs retinotopic territory. Point spread of the fMRI signal has been estimated to be on the order of just a few millimeters (Engel, Glover, & Wandell, 1997;Sereno et al, 1995), but recent estimates suggested spread of approximately 7 mm at half-width-at-half-maximum (HWHM; Cornelissen et al, 2006). According to an estimate of V1 cortical magnification (Sereno et al, 1995), the distance from the inner to the outer border of the probing region projected on V1 is about 15 mm.…”

“…To demonstrate this property in human visual cortex with fMRI, we used a slow event-related design in which changes between high and low inducer luminance levels were separated by several seconds, thereby taking into account the slow fMRI hemodynamic signal (Logothetis, Pauls, Augath, Trinath, & Oeltermann, 2001;Boynton, Engel, Glover, & Heeger, 1996). Furthermore, we optimized the spatial dimensions of the stimulus to take into account the spatial resolution limits of the fMRI signal (Cornelissen, Wade, Vladusich, Dougherty, & Wandell, 2006;Sereno et al, 1995) and limits in the spatial extent of brightness induction (Pereverzeva & Murray, 2008). A possible brightness-related antiphase signal in the probing Maastricht University *These authors contributed equally to the study.…”