An event-related brain potential study of inhibition of return

Event-related brain potentials (ERPs) were recorded during two spatial-cuin g experiments using nonpredictive cues. Our primary goal was to determine t he electrophysiological consequences of inhibition of return (IOR). At long (>500 msec) cue-target intervals, subjects responded more slowly to target s that appeared at or near the cued location, relative to targets that appe ared on the opposite side of fixation from the cue. This behavioral IOR eff ect was associated with cue-validity effects on several components of the t arget-elicited ERP waveforms. The earliest such effect was a smaller occipi tal P1 on valid-cue trials, which we interpret as a P1 reduction. The P2 co mponent was also smaller on valid-cue trials, indicating that nonpredictive spatial cues influence multiple stages of information processing at long c ue-target intervals. Both of these effects were observed when sensory inter actions be tween cue and target were likely to be negligible, indicating th at they were not caused by sensory refractoriness. A different effect of cu e validity, the posterior negative difference, was found when sensory inter actions were likely to be greatest, indicating that it could arise from sen sory refractoriness.