Functional brain imaging of the Rotating Snakes illusion by fMRI

The neural basis of illusory motion perception evoked from static images has not been established well. We examined changes in neural activity in motion sensitive areas of the human visual cortex by using functional magnetic resonance imaging (fMRI) technique when a static illusory-motion image ('Rotating Snakes') was presented to participants. The blood-oxygenation-level dependent (BOLD) signal changes were compared between the test stimulus that induced illusory motion perception and the control stimulus that did not. Comparison was also made between those stimuli with and without eye movements. Signal changes for the test stimulus were significantly larger than those for the control stimulus, if accompanied by eye movements. On the other hand, the difference in signal changes between test and control stimuli was smaller, if steady fixation was required. These results support the empirical finding that this illusion is related to some component of eye movements.