The perception of moving objects and our successful interaction with them entail that the visual system integrates shape and motion information about objects. However, neuroimaging studies have implicated different human brain regions in the analysis of visual motion1,2 (medial temporal cortex; MT/MST) and shape3,4 (lateral occipital complex; LOC), consistent with traditional approaches in visual processing that attribute shape and motion processing to anatomically and functionally separable neural mechanisms. Here we demonstrate object-selective fMRI responses (higher responses for intact than for scrambled images of objects) in MT/MST, and especially in a ventral subregion of MT/MST, suggesting that human brain regions involved mainly in the processing of visual motion are also engaged in the analysis of object shape.
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We would like to thank A. Dale, B. Fischl, D. Greve, A. van der Kouwe and T. Kammer for their help with imaging, A. Höpfner for technical help with the data collection and N. Aguilar and M. Thangarajh for their help with data analysis. We would also like to thank the following people for comments and suggestions: D. Cunningham, N. Kanwisher, N. Logothetis, M. Sereno, N. Sigala, S. Smirnakis, and A. Tolias. This work was supported by the Max Planck Society and a Mc Donnell-Pew grant # 3944900 to Z.K.
Examples of stimuli used in the study. Intact and scrambled images of two-dimensional silhouettes of the objects used. The variety of the stimuli used indicates that the results observed were not due to visual or semantic properties associated with a specific stimulus type, but were due to the different properties defining the object shape across conditions (that is, motion, disparity, shading, two-dimensional contours).
Event-related time courses. Time courses (percent signal change from the fixation baseline trials for 10 time points) selectively averaged for each stimulus condition (intact and scrambled images of 2D objects, moving objects, stereo objects and shaded objects) across trials, scans and subjects in (a) MT/MST and (b) the LOC. Trials start at time = 0 s.
Object-selective responses in MT/MST subregions. Object-selectivity index (percent signal change for intact images percent signal change for scrambled images) for each object type (2D objects, moving objects, stereo objects, shaded objects) in the overlap region between MT/MST and the LOC, and the non-overlap region (that is, voxels in MT/MST that did not overlap with voxels in the LOC). These regions were defined based on the functional maps shown in Fig. 1 (see text). The error bars indicate standard errors on the percent signal change averaged across scans and subjects.
Shape-selective responses for grayscale images versus outlines. Average percent signal increases (from the fixation baseline trials) for intact and scrambled grayscale photographs and outlines of objects in MT/MST (a) and the LOC (b). These stimuli were used to localize independently the LOC in each subject. A similar pattern of results was observed for these stimuli as the findings described in the manuscript. Specifically, significantly stronger responses to intact than to scrambled images were observed in MT/MST for grayscale images of objects that contain 3D information (F1,19 = 165.1, p = 0.001) but not for 2D outlines (F1,19 < 1, p = 0.40). In contrast, the responses in the LOC were stronger for intact than for scrambled images for both grayscale pictures (F1,19 = 532.2, p = 0.001) and outlines (F1,19 = 101.3, p = 0.001). The graphs show the average of the percent signal change across four 16-s blocks for each stimulus condition across scans and 20 subjects (8 subjects that participated in the experiment reported in this manuscript and 12 additional subjects). The error bars indicate standard errors on the percent signal change averaged across scans and subjects.