Coding of 3D curvature in the parietal cortex (area CIP) of macaque monkey

We investigated responses of area CIP of macaque monkey to a set of 3D curvatures defined by random-dot stereogram (RDS). In 82 neurons recorded, 75 (91.5 %) had significant response to one of curvatures tested. Most of visually responsive neurons showed preference to curvature with convex or concave. To evaluate the strength of tuning to the shape, modulation index (MI) was computed for the responses of each neuron to the curvatures, and neuron with MI more than 0.6 was defined as ‘curvature selective neuron’. Of 75 visually responsive neurons, 20 (26.7 %) met the criterion. Five neurons had highly selective response to a particular curvature (MI >= 0.8). Then we plotted the preferred shape index of the curvature selective neurons computed from Gaussian function fit to the responses of neurons. The distribution of the preferred shape index was biased toward concave and convex ellipsoid, although it distributed over the range of shape index (−1.0 − 1.0). These results suggest that 3D curvatures might be represented in area CIP and this area plays a critical role in 3D vision.