MT cells respond to retinal image motion, whether the motion results from stimulus movement or eye movement (Bair and O'Keefe, Vis. Nsci. 1988; Ilg, EBR 1997). But experiments in area MT have identified extra-retinal signals related to eye position and eye velocity (Squatrito and Maoli, J. Neurosci 1997.; Bremmer, et al. J. Neurophys. 1997). These signals suggest that MT cells may modify their visual responses during eye movements. We have therefore studied the way that responses to visual motion in MT cells change during smooth pursuit eye movements. We recorded responses from direction-selective MT neurons in two rhesus macaques. We measured speed tuning along the preferred-null axis for random texture stimuli presented during both fixation and pursuit. Receptive field stimulation was constant across eye movement conditions. We also assessed the extra-retinal inputs for different eye positions and smooth eye velocities in the absence of receptive field stimuli. Most MT cells' visual responses did not change during pursuit. In a minority of cells, responses increased or decreased during pursuit, but selectivity for the speed of retinal motion did not change. A few cells also responded systematically to changes in eye velocity or position in the absence of a receptive field stimulus. The visual response changes we observed in area MT during smooth pursuit were similar in kind, but smaller in both frequency and magnitude than those in neighboring area MST (Chukoskie and Movshon, VSS 2001). These results suggest that although most area MT cells encode retinal image motion veridically, other MT cells may contribute to motion processing in a observer-centered coordinate frame.
ASJC Scopus subject areas
- Sensory Systems