Functional organization of three-dimensional orientation encoding within the visual cortex

Visual perception of three-dimensional (3D) structure is important for object recognition, grasping, and manipulation. The 3D 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 3D planar surfaces with linear gradients defined by horizontal binocular disparity while measuring fMRI activity to test whether the representation of 3D surface tilt is functionally organized within visual cortex. We find functionally defined structures within V3A and V7. Most notably, in one participant 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 3D 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.