Studies in primate physiology and human functional neuroimaging have convincingly shown that the area of the brain termed MT/V5+-which includes the middle temporal visual area MT/V5 along with adjacent motion-sensitive areas such as MST-is involved in the processing of motion information. Tootell et al.  showed that the blood oxygenation level dependent (BOLD) signal measured by functional magnetic resonance imaging (fMRI) in the human MT/V5+ seemingly correlates with the strength of perceived motion aftereffect (MAE), the illusory motion of a stationary pattern that one sees after adapting to a moving pattern. The signal in MT/V5+ decayed slowly during the period when the MAE was seen. It is possible that this slow decrease in MT/V5+ activity was unrelated to the perceptual experience of motion. After replicating Tootell et al.'s experiment, a modified version of the experiment was concluded in which a blank period was inserted between the adapting motion stimulus and the stationary testing pattern. The results demonstrated that MT/V5+ activity indeed decayed more slowly after an effective unidirectional motion adaptation than after bidirectional adaptation, without corresponding perception of MAE. Nevertheless, in a more conclusive experiment, we adapted observers to a unidirectional motion for a very long period and showed that the activity in MT/V5+ changed in synchrony with the presence and absence of perceived MAE, simply as a result of presenting a stationary visual stimulus in and out of the adapted retinal region.
Bibliographical noteFunding Information:
We thank Patty Costello and Essa Yacoub for their help in running the fMRI experiments, Patrick Cavanagh for commenting on the manuscript, and our volunteers for their cooperation. Supported by University of Minnesota start-up fund, Grant-in-Aid to S.H. and NIH grant R01 MH55346 to X.H.