Decoding chromatically-tuned suppressive fields in early visual cortex

Abstract

Visual cortex is known to contain neurons with extended, suppressive, extraclassical receptive fields. The effects of these fields on neural responses are poorly understood at a population level. For example, if these extraclassical receptive fields are chromatically tuned, neuronal populations whose surrounds lie within directly-stimulated regions might contain information about stimulus chromaticity even though their classical receptive fields are not stimulated directly. Here, we tested this hypothesis using an fMRI multivariate pattern classification technique. We showed that fMRI BOLD signals in both peripheral V1 and V2 carry information about foveal stimulus color. These regions, containing neurons whose classical receptive fields do not overlap with the stimulus location, were as informative about stimulus color as regions driven by the stimulus directly. Most voxels in the periphery exhibited a reduction in their BOLD signal in response to the central stimulus and classification was supported by these suppressed voxels alone. The ability to classify chromatic and achromatic stimuli based on these population responses agrees with recent electrophysiological studies showing that many V1 and V2 neurons have large, chromatically-tuned suppressive surrounds.