The lateral intraparietal area (LIP) contains spatially selective neurons that are partly responsible for determining where to look next, and are thought to serve a variety of sensory, motor planning, and cognitive control functions within this role1,2,3. Notably, according to numerous studies in monkeys4,5,6,7,8,9,10,11,12, area LIP implements a fundamental perceptual process, the gradual accumulation of sensory evidence in favor of one choice (e.g., look left) over another (look right), which manifests as a slowly developing spatial signal during a motion discrimination task. However, according to recent inactivation experiments13,14, this signal is unnecessary for accurate task performance. Here we reconcile these contradictory findings. We designed an urgent version of the motion discrimination task in which there is no systematic lag between the perceptual evaluation and the motor action reporting it, and such that the evolution of the subject’s choice can be tracked millisecond by millisecond15,16,17,18. We found that while choice accuracy increased steeply with increasing sensory evidence, at the same time, the spatial signal became progressively weaker, as if it hindered performance. In contrast, in a similarly urgent task in which the discriminated stimuli and the choice targets were spatially coincident, the neural signal seemed to facilitate performance. The data suggest that the ramping activity in area LIP traditionally interpreted as evidence accumulation likely corresponds to a slow, post-decision shift of spatial attention from one location (where the motion occurs) to another (where the eyes land).
Some rats take more time to make easier perceptual decisions
