Art - Thompson (B)

283 Neural correlates of perceptual decisions have been identified in the visual cortex of monkeys observing weak or ambiguous stimuli1–4. Implicit in such studies is a behavioral report about a sensory event that allows an inference about the subject’s perceptual state. To examine the link between sensation and action, we have used a signal-detection protocol to investigate visual signals in an area of the brain known to be involved in generating behavioral reports. Backward masking by light was used to create a condition in which the same physical stimulus might or might not be detected and localized. Monkeys decided whether and where to shift gaze based on variable neural responses to a visual stimulus with fixed physical properties. We recorded the visual responses of neurons located in the frontal eye field (FEF). FEF is an area located in the prefrontal cortex that is reciprocally connected with many extrastriate visual areas5 and is central to the generation of voluntary eye movements6. We compared neuronal responses during correct and error trials and when the target stimulus was either present or not. This experiment had three purposes. The first was to evaluate the hypothesis that neurons in prefrontal cortex respond only to stimuli that guide action7,8. Visual responses in frontal cortex are dictated more by meaning or by value than by visual features of a stimulus6, but there has been no systematic study of frontal cortex using intermittently visible stimuli that support two alternative reports. The second purpose was to expand on earlier studies of visual cortex using ambiguous stimuli by monitoring sensoryrelated neural activity in an area that is involved in producing the behavioral report. Specifically, we tested the hypothesis that the representation of the visual stimulus by FEF neurons in a backward masking task is sufficient to explain the behavioral response. The third purpose was to better understand the phenomenon of backward masking by testing the proposal that responses to stimuli that are effectively masked by light do not leave the retina9.