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