Integration of local features into global shapes: monkey and human fMRI studies

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Summary the properties of neurons in different visual areas (Hubel and Wiesel, 1968; Felleman and Van Essen, 1991; Van The integration of local image features into global Essen et al., 1992), and in humans, where recent fMRI shapes was investigated in monkeys and humans us- studies provide evidence for functional organization of ing fMRI. An adaptation paradigm was used, in which the visual cortex (Wandell, 1999, for review). The strong stimulus selectivity was deduced by changes in the correlation between the fMRI signal and the underlying course of adaptation of a pattern of randomly oriented neural responses (Logothetis et al., 2001) emphasizes elements. Accordingly, we observed stronger activity the importance of such studies for bridging the gap when orientation changes in the adapting stimulus between the extensive neurophysiological findings in resulted in a collinear contour than a different random monkeys and those reported in combined psychophysipattern. This selectivity to collinear contours was ob- cal and imaging investigations with humans. Our goal served not only in higher visual areas that are impli- was to investigate the visual integration processes in cated in shape processing, but also in early visual both the monkey and the human brain by using the same areas where selectivity depended on the receptive fMRI technique and similar experimental paradigms. field size. These findings suggest that unified shape We tested responses across visual areas to collinear perception in both monkeys and humans involves mul- contours versus random patterns. The collinear patterns tiple visual areas that may integrate local elements to consisted of a number of similarly oriented elements global shapes at different spatial scales. embedded into a background of randomly oriented elements, while the random patterns consisted of a field of randomly oriented elements. Such displays yield the