Abstract
One can perceive the motion of a visual object independent of eye movements that cause additional virtual motions on the retina. To understand the underlying neural mechanisms, we recorded neuronal responses in cortical MT/MST areas to a moving random dot pattern (-160 to 160deg/sec) that appeared briefly on the screen while monkeys performed smooth pursuit or stationary fixation. Although neurons in both areas exhibited substantial responses to the motion of the textured image in the preferred direction, the responses of the MST neurons were mostly correlated with the motion of the image on the screen, independent of pursuit, whereas the responses of MT neurons were mostly correlated with the motion of the image on the retina. When a check pattern of 0.5 cycles/deg was used instead of the random dots and its temporal frequency exceeded 20Hz (0.5 cycles/deg x 40 deg/sec) on the retina, neuronal responses in both areas decreased independent of pursuit eye movements. To confirm this observation, we replaced the check pattern with a different spatial frequency (0.25 cycles/deg). The stimulus speed that gave the best response was 80deg/sec on the retina independent of pursuit eye movements, and the temporal frequency of the visual stimulus was 20Hz (0.25 cycles/deg x 80 deg/sec). The decreased neuronal responses at higher temporal frequencies (>20Hz) supports the idea that the MST neurons code visual motion in the external world while compensating for the eye movements by utilizing the information of the visual motion on the retina and of the eye movements. [J Physiol Sci. 2007;57 Suppl:S101]
