Brain Areas Sensitive to Coherent Visual Motion

Abstract

Detection of coherent motion versus noise is widely used as a measure of global visual-motion processing. To localise the human brain mechanisms involved in this performance, functional magnetic resonance imaging (fMRI) was used to compare brain activation during viewing of coherently moving random dots with that during viewing spatially and temporally comparable dynamic noise. 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 putative V3A, but not in V1. In addition there were foci of activation on the occipital ventral surface, the intraparietal sulcus, and superior temporal sulcus. 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 than by coherent motion, possibly reflecting activation of neurons with a wider range of motion selectivities. This activation was at a more anterior location in the comparison of noise with the faster velocity, suggesting that 20 deg s−1 is beyond the velocity range of the V1 representation of central 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 defined dorsal stream.