THE CONSTRUCTIVE NATURE OF VISION - DIRECT EVIDENCE FROM FUNCTIONAL MAGNETIC-RESONANCE-IMAGING STUDIES OF APPARENT MOTION AND MOTION IMAGERY

Echoplanar functional magnetic resonance imaging was used to monitor a ctivation changes of brain areas while subjects viewed apparent motion stimuli and while they were engaged in motion imagery. Human cortical areas MT (V5) and MST were the first areas of the 'dorsal' processing stream which responded with a clear increase in signal intensity to a pparent motion stimuli as compared with flickering control conditions. Apparent motion of figures defined by illusory contours evoked greate r activation in V2 and MT/MST than appropriate control conditions. Sev eral areas of the dorsal pathway (V3A, MT/MST, areas in the inferior a nd superior parietal lobule) as well as prefrontal areas including FEF and BA 9/46 responded strongly when subjects merely imagined moving s timuli which they had seen several seconds before. The activation duri ng motion imagery increased with the synaptic distance of an area from V1 along the dorsal processing stream. Area MT/MST was selectively ac tivated during motion imagery but not during a static imagery control condition. The comparison between the results obtained with objective motion, apparent motion and imagined motion provides further insights into a complex cortical network of motion-sensitive areas driven by bo ttom-up and top-down neural processes.