MST NEURONS RESPOND TO OPTIC FLOW AND TRANSLATIONAL MOVEMENT

We recorded the responses of 189 medial superior temporal area (MST) n eurons by using optic flow, real translational movement, and combined stimuli in which matching directions of optic flow and real translatio nal movement were presented together. One-half of the neurons (48%) sh owed strong responses to optic flow simulating self-movement in the ho rizontal plane, and 24% showed strong responses to translational movem ent. Combining optic flow stimuli with matching directions of translat ional movement caused substantial changes in both the amplitude of the best responses (44% of neurons) and the strength of direction selecti vity (71% of neurons), with little effect on which stimulus direction was preferred. However, combining optic flow and translational movemen t such that opposite directions were presented together changed the pr eferred direction in 45% of the neurons with substantial changes in th e strength of direction selectivity. These studies suggest that MST ne urons combine visual and vestibular signals to enhance self-movement d etection and disambiguate optic flow that results from either self-mov ement or the movement of large objects near the observer.