Date of Award


Degree Type


Degree Name

Doctor of Philosophy


When an observer's visual attention is involuntarily drawn to a particular spatial location by a highly salient cue, the processing of stimuli appearing at that location is facilitated. When attention is then disengaged from the cued location, subsequent shifts of attention (either voluntary or involuntary) to the same location are inhibited. This inhibition in returning attention to a previously attended location delays the processing of stimuli appearing there, a phenomenon known as inhibition of return (IOR). IOR is a particularly intriguing phenomenon because it suggests that the attentional system has some means of keeping track of previously attended locations. That is, if the "spotlight" of attention can avoid returning to a particular location, then the location in question must somehow be registered or "remembered." In this investigation, the relation between IOR and the visual indexing model of attentional allocation (Pylyshyn, 1989) was examined. According to the visual indexing model, the visual system uses a small number of indices or markers to mediate the engagement of visual attention, and the spotlight of attention can be directly and selectively allocated to multiple indexed locations. It was hypothesized that visual indexing may subserve IOR, in that visual indices could provide a means to register or "remember" previously attended cues. One of the principle findings reported herein is that visual attention can be inhibited from returning to multiple locations. Not only is this a novel empirical finding, it also strongly implies a relation between visual indexing and IOR.



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