Abstract
Predictive coding theories of perception posit that visual stimuli are processed differently when they are expected than when they are unexpected. In this study, we extend that investigation into a new domain: covert exogenous spatial attention. It has long been known that the onsets of task-irrelevant stimuli (“cues”) cause reflexive shifts of attention towards their locations. We asked, do implicit expectations about the likelihood of task-irrelevant cues modulate how strongly they capture attention? Participants discriminated the orientation of a simple line that was preceded, on some trials, by a task-irrelevant disk (the exogenous cue). The color of the fixation dot (red or green) implicitly signaled the probability that a disk would appear (0.8, “expected”, or 0.2, “unexpected”). When presented, this disk flashed briefly, either near the target line (valid cue) or near a distractor line (invalid cue, equally likely). Across several experiments, we varied how much time participants were given to process the stimuli before responding. In short, we found that unexpected disks generated significantly larger cueing effects (discrimination accuracy, valid–invalid) than expected disks, but only when participants responded during the initial phase of visual processing (within 500 ms). Intriguingly, in post-experiment surveys, we found that participants were unable to report what the color of the fixation dot signaled about the likelihood of the cues. Therefore, our data demonstrate that implicitly learned contingencies between irrelevant visual events form expectations that modulate the deployment of attention.