Perceptual decision influences V1 neuronal responses to ambiguous threedimensional objects

We studied spike responses of V1 superficial layer neurons in a perceptual decision task. A rhesus monkey was trained to hold fixation during presentations of a three-dimensional (structure-from-motion) object and to make a perceptual decisions in an alternative choice paradigm while extracellular responses were obtained by single electrode penetrations. The disparity of constituent dots was varied from trial-to-trial to render perceptually ambiguous or unambiguous objects. Neurons with modulated disparity responses were selected. We estimated the certainty at which the firing rate of a given V1 neuron would allow an ideal observer to predict the monkey's perceptual choice in the task. Neuronal responses to zero-disparity (ambiguous) objects were sorted according to the perceptual decision and the choice probability was determined for each neuron (Britten et al., 1996). Based on the sample of n>100 neurons the firing rate ROC curves showed significant bias from chance starting at 500 msec after the stimulus onset. The choice probability was different from 0.5 for the significant majority of cells. The long latency of the perceptual bias in the V1 responses suggests a feed-back from higher visual cortical areas including MT/MST that further raises the question of V1's involvement in perceptual awareness. (Supported by NEI and J.G. Boswell Professorship) Acknowledgments: We thank to Christof Koch and Melissa Saenz for useful discussion