Abstract
In order to attain a correct interpretation of an ambiguous visual stimulus, the brain may have to elaborate on the sensory evidence. Are the same neurons that carry the sensory evidence also involved in generating an interpretation? To address this question, we study the activity of neurons in the primary visual cortex of macaque monkeys involved in a task in which they have to trace a curve mentally, without moving their eyes. Previous results showed that responses of neurons in area V1 to a curve that is traced are enhanced relative to responses to other, distracting curves. This response enhancement provides a correlate of visual attention that is directed to the traced curve. In the present study we investigate whether the response modulation in area V1 depends on the monkey's interpretation, by an analysis of perceptual errors. Monkeys had to trace a curve that came close to another, distracting curve. At this location the two curves could intersect each other, or stay separate. The difficulty of this distinction was varied, and the monkeys therefore ‘took a wrong turn’ on a fraction of the trials. These errors were reflected by alterations in the attentive modulation of neuronal responses in area V1. Indeed, activity in area V1 predicted whether the monkey was going to make an error, and even indicated the location where the monkey lost track of the curve that had to be traced. Receptive fields in area V1 are relatively small, and attentional selection of curve segments may occur at a high spatial resolution. We speculate that the participation of area V1 in perceptual decisions allows this high spatial resolution information to enter into the decision process. We conclude that area V1 contains a high resolution version of the actual interpretation, which may be essential for flawless curve-tracing at locations where different curves come close together.