Activity in monkey V4 reflects target identification and saccade direction in free viewing visual search

Abstract

We studied the activity of V4 neurons in a free viewing visual search task, in which monkeys reported the orientation of a target among distractors and were free to move their eyes. Previously, we reported that activity in the macaque lateral intraparietal area (LIP) in the search task predicted the saccade goal and latency, and also discriminated between targets and distractors even when the monkey made a saccade away from the receptive field. There is a known anatomical connection between V4, an extrastriate area involved in object processing, and LIP. In this experiment, we examined the role of V4 in identification of the target and representation of the saccade direction and compared it to the role of LIP in an identical search task. We trained monkeys on a free viewing visual search task in which they reported the orientation of a target among distractors with a non-targeting hand movement. After the stimuli appeared, the monkeys were free to move their eyes, and they made a first saccade to the target about half the time. We also trained monkeys on a saccade task in which they made a saccade to a single object which could be a target or a distractor from the search task. In the saccade task there was no difference in the early responses evoked by the search target or the search distractor. Here, the monkey attended to the objects by making a saccade, but did not have to discriminate them. When the monkey had to discriminate the objects in the search task, the target evoked a greater response, independent of the direction of the saccade. Like LIP, V4 also displayed a separate signal reflecting the direction of the impending saccade but unlike LIP, this saccadic signal did not correlate with saccadic latency.