My dissertation research is aimed at understanding the attentional mechanisms that mediate visual search. More specifically, my research focuses on a phenomenon called inhibition of return (IOR) where people are slower to respond to a stimulus if it is presented in a location that was previously attended. This delay in response time (RT) is thought to reflect a bias to attend novel locations which, in turn, should serve to improve visual search efficiency. However, the question of whether IOR really plays an important role in visual search has been debated in the literature. My research addresses this question from several angles. One line of research examines whether the bias to attend novel locations reflects facilitation at unattended locations, inhibition at attended locations or both. A second line of research employs a novel paradigm to investigate the role attention has in multiple IOR and the causes of the apparent decline in IOR over multiple locations. A third line of research couples the novel paradigm for investigating multiple location IOR with more traditional visual search paradigms. And a fourth line of research examines whether multiple IOR is location-based, object-based or both.; The first section of this thesis presents the paradigms used to study attention, and IOR, in particular. The second section reviews the evidence supporting a functional role of IOR in visual search. The third section presents my own studies that demonstrate that attention is important for establishing multiple IOR, that both the addition of cued locations and decay processes are responsible for the decline in IOR across cued back locations, that IOR is of greater benefit when visual search is difficult, and that multiple location IOR is coded in spatial coordinates.
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