Abstract
After the appearance of peripheral, non-predictive cues, participants respond faster to targets appearing at the cued location when the time that elapses in between the cue and target is short and they respond more slowly when this time is longer. Traditionally, this pattern of early facilitation and later inhibition has been interpreted as indexing two separate, but related, components of orienting spatial attention. Namely, after the peripheral cue catches the participants' attention (attentional capture), they are slower to reorient to this previously attended and unmeaningful location (inhibition of return). One problem with this interpretation is that inhibition of return can be observed when no evidence of attentional capture is obtained (e.g., Maylor, 1985). Here, we describe the neurophysiological correlates of these behavioral effects. The activity of single neurons in the superficial and intermediate layers of the superior colliculus was recorded while monkeys performed a non-predictive, cue-target task. In all experimental sessions, inhibition of return was obtained in behavior and was associated with attenuated target-aligned activity of visual and visuomotor neurons in the superficial and intermediate layers. In many sessions, attentional capture was also observed, which was associated with enhanced target-aligned activity because residual activity from the cue augmented the incoming activity from the target. In some sessions, however, attentional capture was not found. In these instances, the target-aligned signal tended to be reduced. Taken together, attentional capture, the absence of attentional capture, and inhibition of return arise from a continuum of sensory processing.