Chandrasekaran C, Canon V, Dahmen JC, Kourtzi Z, Welchman AE. Neural correlates of disparity-defined shape discrimination in the human brain. J Neurophysiol 97: [1553][1554][1555][1556][1557][1558][1559][1560][1561][1562][1563][1564][1565] 2007. First published December 6, 2006; doi:10.1152/jn.01074.2006. Binocular disparity, the slight differences between the images registered by our two eyes, provides an important cue when estimating the three-dimensional (3D) structure of the complex environment we inhabit. Sensitivity to binocular disparity is evident at multiple levels of the visual hierarchy in the primate brain, from early visual cortex to parietal and temporal areas. However, the relationship between activity in these areas and key perceptual functions that exploit disparity information for 3D shape perception remains an important open question. Here we investigate the link between human cortical activity and the perception of disparity-defined shape, measuring fMRI responses concurrently with psychophysical shape judgments. We parametrically degraded the coherence of shapes by shuffling the spatial position of dots whose disparity defined the 3D structure and investigated the effect of this stimulus manipulation on both cortical activity and shape discrimination. We report significant relationships between shape coherence and fMRI response in both dorsal (V3, hMTϩ/V5) and ventral (LOC) visual areas that correspond to the observers' discrimination performance. In contrast to previous suggestions of a dichotomy of disparity-related processes in the ventral and dorsal streams, these findings are consistent with proposed interactions between these pathways that may mediate a continuum of processes important in perceiving 3D shape from coarse contour segmentation to fine curvature estimation. I N T R O D U C T I O NEveryday human behavior depends on the brain estimating the depth structure of the nearby environment so that we can avoid dangers and exploit opportunities. A powerful source of information to depth structure is provided by the slight differences between the retinal images registered by our two eyes (binocular disparity). The brain's use of binocular disparity has been studied extensively Howard and Rogers 2002), largely because of the quantitative relation between disparity and the depth structure of the environment (Longuet-Higgins 1982), the exquisite sensitivity of the brain to disparity (Westheimer and McKee 1978), and the observation that horizontal binocular disparity provides a powerful impression of depth even under impoverished viewing conditions (Julesz 1971).Neurophysiological and imaging studies revealed selectivity for binocular disparity at multiple levels of the visual hierarchy in the monkey and the human brain from early visual areas, to object-and motion-selective areas and the parietal cortex (for reviews see Cumming and DeAngelis 2001;Neri 2005; Orban et al. 2006a,b;Parker 2004). However, understanding how activity in these multiple disparity-selectivity regions relates to k...