Tight correlation between the time course of sensory and motor estimates

Leslie Osborne,1 William Bialek,2 and Steve Lisberger1

2Princeton University

The sensory task of the smooth pursuit system is to extract an estimate of target velocity from image motion on the retina, and its motor task is to accelerate the eyes to match target velocity. We have quantified the directional accuracy of early pursuit eye movements and related this to the cortical sensory signals in visual area MT likely to mediate the behavior. We computed the signal-to-noise ratio as a function of time in primate eye velocity responses to visual targets whose trajectories differ by small angles. We found that about 80% of the final directional accuracy of the eye movement is achieved within its first 100ms. In seperate experiments in anesthetized macaques, we measured the responses of single units in MT to moving stimuli differing by small angles. Computing the time course of direction information available in MT responses, we found that neurons also provide about 80% of their maximal information within the first 100ms of their responses. Therefore, target direction information can be extracted from single units as quickly as behavioral performance requires it. Individual MT neurons were much less directionally accurate than the eye movement itself, necessitating a mechanism for pooling information from many neurons to achieve the observed behavioral accuracy.