NEURONAL SELECTIVITIES TO COMPLEX OBJECT FEATURES IN THE VENTRAL VISUAL PATHWAY OF THE MACAQUE CEREBRAL-CORTEX

1. To infer relative roles of cortical areas at different stages of th e ventral visual pathway, we quantitatively examined visual responses of cells in V2, V4, the posterior part of the inferotemporal cortex (p osterior IT), and the anterior part of the inferotemporal cortex (ante rior IT), using anesthetized macaque monkeys. 2. The critical feature for the activation was first determined for each recorded cell by usin g a reduction method. We started from images of three-dimensional comp lex objects and simplified the image of effective stimuli step by step by eliminating a part of the features present in the image. The simpl est feature that maximally activated the cell was determined as the cr itical feature. The response to the critical feature was then compared with responses of the same cell to a routine set of 32 simple stimuli , which included white and black bars of four different orientations a nd squares or spots of four different colors. 3. Cells that responded maximally to particular complex object features were found in posterio r IT and V4 as well as in anterior IT. The cells in posterior IT and V 4 were, however, different from the cells in anterior IT in that many of them responded to some extent to some simple features, that the siz e of the receptive field was small, and that they intermingled in sing le penetrations with cells that responded maximally to some simple fea tures. The complex critical features in posterior IT and V4 varied; th ey consisted of complex shapes, combinations of a shape and texture, a nd combinations of a shape and color. 4. We suggest that local neurona l networks in V4 and posterior IT play an essential role in the format ion of selective responses to complex object features.