Curvature-processing network in macaque visual cortex

Significance The brain processes visual stimuli along different feature dimensions, including edge orientation, visual motion, and color. To expedite visual processing, cells that process a common visual dimension are often anatomically grouped in cortical columns, patches, and/or areas. Here, we tested the hypothesis that (i) image curvature is one of these fundamental visual dimensions and, as such, (ii) curvature-selective cells are grouped together in discrete cortical areas. Using neuroimaging techniques, we confirmed this hypothesis and localized the curvature-processing sites in extrastriate visual cortex. These sites lay along a common cortical strip, spanning lower- to higher-level processing stages. Furthermore, the curvature-processing sites are adjacent to the well-known face-processing cortical areas, suggesting a possible functional link between them. Our visual environment abounds with curved features. Thus, the goal of understanding visual processing should include the processing of curved features. Using functional magnetic resonance imaging in behaving monkeys, we demonstrated a network of cortical areas selective for the processing of curved features. This network includes three distinct hierarchically organized regions within the ventral visual pathway: a posterior curvature-biased patch (PCP) located in the near-foveal representation of dorsal V4, a middle curvature-biased patch (MCP) located on the ventral lip of the posterior superior temporal sulcus (STS) in area TEO, and an anterior curvature-biased patch (ACP) located just below the STS in anterior area TE. Our results further indicate that the processing of curvature becomes increasingly complex from PCP to ACP. The proximity of the curvature-processing network to the well-known face-processing network suggests a possible functional link between them.