A large proportion of the neurons in the rostral lower bank of the Superior Temporal Sulcus, which is part of IT, respond selectively to disparity-defined 3D shape (Janssen et al., 1999; Janssen et al., 2000). These IT neurons preserve their selectivity for different positions-in-depth, which proves that they respond to the spatial variation of disparity along the vertical axis of the shape (higher-order disparity selectivity). We have studied the responses of neurons in parietal area AIP, the end stage of the dorsal visual stream and crucial for object grasping, to the same disparity-defined 3D shapes (Srivastava et al., 2009). In this presentation I will review the differences between IT and AIP in the neural representation of 3D shape. More recent studies have investigated the role of AIP and IT in the perceptual discrimination of 3D shape using simultaneous recordings of spikes and local field potentials in the two areas, psychophysics and reversible inactivations. AIP and IT show strong synchronized activity during 3D-shape discrimination, but only IT activity correlates with perceptual choice. Reversible inactivation of AIP produces a deficit in grasping but does not affect the perceptual discrimination of 3D shape. Hence the end stages of both the dorsal and the ventral visual stream process disparity-defined 3D shape in clearly distinct ways. In line with the proposed behavioral role of the two processing streams, the 3D-shape representation in AIP is action-oriented but not crucial for 3D-shape perception.
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