Perceptual similarity representations beyond the sensory cortex

It is commonly thought that information supporting conscious perception is primarily represented in sensory cortices, whereas association cortex encodes more abstract, task-dependent information. However, this impression may partly stem from difficulties in experimentally assessing the functions of association areas characterized by mixed selectivity and complex spatial topography. Here, we combined repetition-suppression (RS) and multi-voxel pattern analysis (MVPA) to extract richer information from human fMRI. With this approach, we asked whether association regions represent the perceptual similarity structure among color stimuli, although this perceptual similarity information was task-irrelevant in the experiment. Our analysis revealed such representations beyond the visual cortex, in lateral prefrontal, and parietal regions. We further demonstrated an electrophysiological complement to the fMRI findings by applying the same approach to local field potentials recorded in the macaque dorsomedial parietal cortex. Our findings suggest that higher-order areas beyond the visual cortex may play a key role in subjective color perception.