A neural code for three-dimensional object shape in macaque inferotemporal cortex

Previous investigations of the neural code for complex object shape have focused on two-dimensional (2D) pattern representation. This might be the primary mode for object vision, based on simplicity and direct relation to the retinal image. In contrast, 3D shape representation requires higher-dimensional coding based on extensive computation. Here, for the first time, we provide evidence of an explicit neural code for complex 3D object shape. We used a novel evolutionary stimulus strategy and linear/nonlinear response models to characterize 3D shape responses in macaque monkey inferotemporal cortex (IT). We found widespread tuning for 3D spatial configurations of surface fragments characterized by their 3D orientations and joint principal curvatures. Configural representation of 3D shape could provide specific knowledge of object structure critical for guidance of complex physical interactions and evaluation of object functionality and utility.