| Inhibition of return (IOR) refers to the finding that targets at cued locations are responded to more slowly than targets at uncued locations when a relatively long interval occurs between the two events. An early and still dominant explanation is that IOR is a mechanism that biases us toward novelty to increase the efficiency of search. This idea has rarely been explicitly tested, however, given a lack of agreement regarding how to measure IOR in search tasks. The present thesis uses variations of the multiple cuing paradigm to address two noticeable gaps in the IOR literature relating to visual search.; First, although there is some evidence consistent with IOR influencing visual search, there is no explicit evidence that IOR can accrue to a recently attended location if attention is rapidly shifted to new locations every 50 ms---the speed at which attention is thought to shift in normal visual search. In Experiments 1-3, participants observed cues that were of either a short (50 ms) or long (500 ms) duration prior to a detection target. The results showed that IOR can accrue at up to four locations with multiple rapid shifts of attention, quickly enough to facilitate visual search.; Second, the magnitude of IOR is greater at more recently cued locations. Experiments 4-7 attempted to discriminate two explanations for this pattern: decay as a function of time vs. interference from intervening cues. Across experiments, time was held constant and the number of cues preceding target onset was manipulated. Counter-intuitively, the results demonstrated that IOR increased as the number of cues on a trial increased, suggesting that IOR might actually increase as attention continually shifts during visual search. Accordingly, IOR is observed outside of the normal temporal parameters with continual shifts of attention in Experiment 8.; These results fit with both attentional and oculomotor accounts of IOR, and suggest a strong role for IOR in visual search, with its influence increasing as the number of shifts of attention increases. Collectively, these findings shed considerable light on IOR: It appears to be faster acting, longer lasting, and more pervasive than originally thought. |
