Testing for functional organization of three-dimensional surface tilt encoding within visual cortex

Abstract

Visual perception of three-dimensional structure is important for object recognition, grasping, and manipulation. The three-dimensional structure of a surface can be defined in terms of its slant and tilt. Previous work has shown that slant and tilt are represented in the posterior and ventral intraparietal sulcus of the human brain; however, it is unclear whether the representation of these features is functionally organized within this region. Here we use phase-encoded presentation of 3-D planar surfaces with linear gradients defined by horizontal binocular disparity while measuring fMRI activity to test whether the representation of 3-D orientation, both for slant and tilt, is functionally organized within the visual cortex. We find functionally defined structures within V3A and V7 for both slant and tilt. Most notably, in two participants we find that the tilt preference is unilaterally organized in a pinwheel-like structure, similar to those observed for orientation preference in V1, which encompasses most of area V3A. These findings indicate that 3-D orientation is functionally organized within the human visual cortex, and the evidence suggesting the presence of a large pinwheel-like structure indicates that this type of organization may be applied canonically within the brain at multiple scales.