Neuronal encoding of the distance traversed by covert shifts of spatial attention.

Neurons in monkey medial superior temporal cortex selectively respond to the patterned visual motion in optic flow that simulates observer self-movement. We trained monkeys in a task that required behavioral responses indicating the location of a precue or the simulated heading direction in a subsequent optic flow stimulus. Medial superior temporal neuronal responses contained transient peaks at latencies proportionate to the distance from the precue to the heading direction represented by the subsequent optic flow. We conclude that these response transients reveal neural mechanisms underlying covert shifts of spatial attention and that the varying latency of these transients reflect the time required for reorientation between attentional targets.