Representation of a perceptual decision in developing oculomotor commands

Behaviour often depends on the ability to make categorical judgements about sensory information acquired over time. Such judgements require a comparis on of the evidence favouring the alternatives(1-4), but how the brain forms these comparisons is unknown. Here we show that in a visual discrimination task, the accumulating balance of sensory evidence favouring one interpret ation over another is evident in the neural circuits that generate the beha vioural response. We trained monkeys to make a direction judgement about dy namic random-dot motion(5) and to indicate their judgement with an eye move ment to a visual target We interrupted motion viewing with electrical micro stimulation of the frontal eye field and analysed the resulting, evoked eye movements for evidence of ongoing activity associated with the oculomotor response(6-10). Evoked eye movements deviated in the direction of the monke y's judgement. The magnitude of the deviation depended on motion strength a nd viewing time. The oculomotor signals responsible for these deviations re flected the accumulated motion information that informed the monkey's choic es on the discrimination task. Thus, for this task, decision formation and motor preparation appear to share a common level of neural organization.