Visual perception of motion and 3-D structure from motion: an fMRI study

Functional magnetic resonance imaging was used to study the cortical bases of 3-D structure perception from visual motion in human. Nine subjects unde rwent three experiments designed to locate the areas involved in (i) motion processing (random motion versus static dots). (ii) coherent motion proces sing (expansion/contraction versus random motion) and (iii) 3-D shape from motion reconstruction (3-D surface oscillating in depth versus random motio n). Two control experiments tested the specific influence of speed distribu tion and surface curvature on the activation results. All stimuli consisted of random dots so that motion parallax was the only cue available for 3-D shape perception. As expected, random motion compared with static dots indu ced strong activity in areas V1/V2. V5+ and the superior occipital gyrus (S OG; presumptive V3/V3A). V1/V2 and V5+ showed no activity increase when com paring coherent motion (expansion or 3-D surface) with random motion. Conve rsely, V3/V3A and the dorsal parieto-occipital junction were highlighted in both comparisons and showed gradually increased activity for random motion , coherent motion and a curved surface rotating in depth, which suggests th eir involvement in the coding of 3-D shape from motion. Also, the ventral a spect of the left occipito-temporal junction was found to be equally respon sive to random and coherent motion stimuli, but showed a specific sensitivi ty to curved 3-D surfaces compared with plane surfaces. As this region is a lready known to be involved in the coding of static object shape, our resul ts suggest that it might integrate various cues for the perception of 3-D s hape.