a1 Department of Neurobiology, Stanford University School of Medicine, Stanford
a2 Howard Hughes Medical Institute and Center for Neural Science, New York University, New York
We have previously documented the exquisite motion sensitivity of neurons in extrastriate area MT by studying the relationship between their responses and the direction and strength of visual motion signals delivered to their receptive fields. These results suggested that MT neurons might provide the signals supporting behavioral choice in visual discrimination tasks. To approach this question from another direction, we have now studied the relationship between the discharge of MT neurons and behavioral choice, independently of the effects of visual stimulation. We found that trial-to-trial variability in neuronal signals was correlated with the choices the monkey made. Therefore, when a directionally selective neuron in area MT fires more vigorously, the monkey is more likely to make a decision in favor of the preferred direction of the cell. The magnitude of the relationship was modest, on average, but was highly significant across a sample of 299 cells from four monkeys. The relationship was present for all stimuli (including those without a net motion signal), and for all but the weakest responses. The relationship was reduced or eliminated when the demands of the task were changed so that the directional signal carried by the cell was less informative. The relationship was evident within 50 ms of response onset, and persisted throughout the stimulus presentation. On average, neurons that were more sensitive to weak motion signals had a stronger relationship to behavior than those that were less sensitive. These observations are consistent with the idea that neuronal signals in MT are used by the monkey to determine the direction of stimulus motion. The modest relationship between behavioral choice and the discharge of any one neuron, and the prevalence of the relationship across the population, make it likely that signals from many neurons are pooled to form the data on which behavioral choices are based.
(Received February 24 1995)
(Accepted May 30 1995)
p1 Present address of K.H. Britten: Center for Neuroscience, University of California, Davis, Davis, CA 95616, USA.
p2 Present address of M.N. Shadlen: Department of Physiology, and Washington Regional Primate Research Center, University of Washington, Seattle, WA 98195, USA.
p3 Present address of S. Celebrini: Centre de Recherche Cerveau et Cognition, CNRS-UPS, Faculte de Medecine Rangueil, 31062 Toulouse, France.
Reprint requests to: William T. Newsome, Department of Neurobiology, Stanford University School of Medicine, Stanford, CA 94305, USA.