Abstract
Inhibition of return (IOR), the slowing of reaction times to a target presented at a location that was cued more than some 300 ms earlier, is usually attributed to attentional or oculomotor mechanisms. The sensory influence of the cue (i.e. masking) is ignored as such sensory effects are believed to occur within a much shorter time-range. The attentional and oculomotor accounts of IOR would predict independence of IOR from similarity between the cue and the target, as long as the cue is equally effective in drawing attention and the target is equally detectable. We asked whether saccadic reaction times (SRT) to a pre-cued location are sensitive to a difference in orientation between the cue and the saccade target; in particular for stimulus timings that are common in IOR paradigms. We first tested the influence of the brief bilateral presentation of oriented stimuli (Gaussian windowed sine-wave gratings) on SRT to a unilateral grating presented at a stimulus-onset-asynchrony (SOA) of 100, 250, 450 or 650 ms. The target was similar to the cue(s), but of a lower contrast and rotated by 0°, 45° or 90°. SRT showed a strong dependence on rotation for the shortest SOAs, as can be expected from masking of the target by the cue. More interestingly, some dependence on rotation was still found with the 450 and 650-ms SOA. In a subsequent experiment we tested the effect of rotation on IOR (uncued location – cued location SRT) by presenting a single cue (the proper IOR paradigm), with an SOA of 650 ms. We observed that IOR was larger when the orientation of the cue was the same as the orientation of the target. Our results indicate that inhibited visual processing of a repeated stimulus can contribute to IOR independently of a spatial attention bias.
Swiss National Sicence Foundatoin Project PBGEP1-125961.