The effects of implicit attentional learning and habituation on inhibition of return.

In two experiments, the effects of implicit attentional learning and habituation on inhibition of return (IOR) were assessed. Experiment 1 consisted of an informative variant of the spatial cuing paradigm (Posner, 1980), with the target appearing most often at the location next to the cue. Short-term as well as long-term learning of the regularities could be observed. This learning took place even though the participants were not able to verbalize the learned information, suggesting that the learning was implicit. By spatially separating the effects of implicit learning and IOR, we demonstrated that the magnitude of IOR slightly decreased because of long-term implicit orienting. In Experiment 2, a noninformative variant of the spatial cuing paradigm, IOR was still found to decrease over the course of the experiment. This suggests that habituation due to the mere repeated initiation of IOR also affects the magnitude of the IOR. This theory is supported by the finding that IOR recovered after short breaks in Experiment 2. However, habituation presumably only played a secondary role in Experiment 1. In sum, IOR was abolished by neither implicit attentional learning nor habituation. Here, the finding that IOR is not easily replaced by implicitly learned orienting clearly indicates that IOR is a powerful, low-level mechanism. We discuss implications of these results for the debate on the function of IOR.