RESPONSES OF NEURONS IN MACAQUE MT TO STOCHASTIC MOTION SIGNALS

Dynamic random-dot stimuli have been widely used to explore central me chanisms of motion processing. We have measured the responses of neuro ns in area MT of the alert monkey while we varied the strength and dir ection of the motion signal in such displays. The strength of motion i s controlled by the proportion of spatiotemporally correlated dots, wh ich we term the correlation of the stimulus. For many MT cells, respon ses varied approximately linearly with stimulus correlation. When they occurred, nonlinearities were equally likely to be either positively or negatively accelerated. We also explored the relationship between r esponse magnitude and response variance for these cells and found, in general agreement with other investigators, that this relationship con forms to a power law with an exponent slightly greater than 1. The var iance of the cells' discharge is little influenced by the trial-to-tri al fluctuations inherent in our stochastic display, and is therefore l ikely to be of neural origin. Linear responses to these stochastic mot ion stimuli are predicted by simple, low-level motion models incorpora ting sensors having relatively broad spatial and temporal frequency tu ning.