Neural activity in the parietal priority map explains saccadic reaction times.

Abstract

Reaction times (RTs) are commonly used to infer the attentional state of the brain, however a direct neural correlate for RTs under these conditions is unknown, although there is growing evidence that neuronal activity can explain RTs in decision making tasks. We propose that reaction times directly represent the state of activity on a priority map, using inhibition of return (IOR) as an exemplar. We have previously shown that the neural responses in LIP play an important role in guiding efficient visual search by suppressing the responses to an inspected target. We suggested that this suppression is a neurophysiological correlate of IOR; by suppressing activity on the map, gaze should not return to items that have already been examined. In this study, we aimed to show that this activity can explain the slowing of RTs at a pre-attended location. We trained two animals to perform a visual foraging task in which they had to find a reward loaded T among 5Ts and 5 distractors. On 50 % of trials the search display disappeared and a probe flashed immediately at one of 10 locations. The animals' RTs to the probe were analyzed depending on the class of the object and whether it had been looked at prior to the probe appearing. We found that RTs were quickest to a T that had not been examined and significantly slower to Ts that had been looked at and distractors. We found that the results could be explained as a function of the neural activity in LIP based on a rise to threshold model incorporating neural adaptation. We conclude that RTs are a direct representation of activity in a priority map and that, under constrained conditions, RTs correlate with attention because priority maps are used to allocate attention.

NIH Grant EY019273, The McKnight Foundation.