Brain areas sensitive to coherent visual motion

Detection of coherent motion versus noise is widely used as a measure of gl obal visual-motion processing. To localise the human brain mechanisms invol ved in this performance, functional magnetic resonance imaging (fMRI) was u sed to compare brain activation during viewing of coherently moving random dots with that during viewing spatially and temporally comparable dynamic n oise, Rates of reversal of coherent motion and coherent-motion velocities ( 5 versus 20 deg s(-1)) were also compared. Differences in local activation between conditions were analysed by statistical parametric mapping. Greater activation by coherent motion compared to noise was found in V5 and putati ve V3A, but not in V1. In addition there were foci of activation on the occ ipital ventral surface, the intraparietal sulcus, and superior temporal sul cus. Thus, coherent-motion information has distinctive effects in a number of extrastriate visual brain areas. The rate of motion reversal showed only weak effects in motion-sensitive areas. V1 was better activated by noise t han by coherent motion, possibly reflecting activation of neurons with a wi der range of motion selectivities. This activation was at a more anterior l ocation in the comparison of noise with the faster velocity, suggesting tha t 20 deg s(-1) is beyond the velocity range of the V1 representation of cen tral visual field. These results support the use of motion-coherence tests for extrastriate as opposed to V1 function. However, sensitivity to motion coherence is not confined to V5, and may extend beyond the classically defi ned dorsal stream.