Visual selection mediated by location: Feature-based selection of noncontiguous locations

Abstract

Experiments using two different methods and three types of stimuli tested whether stimuli at non- adjacent locations could be selected simultaneously. In one set of experiments, subjects attended to red digits presented in multiple frames with green digits. Accuracy was no better when red digits ap- peared successively than when pairs of red digits occurred simultaneously, implying allocation of at- tention to the two locations simultaneously. Different tasks involving oriented grating stimuli produced the same result. The final experiment demonstrated split attention with an array of spatial probes. When the probe at one of two target locations was correctly reported, the probe at the other target lo- cation was more often reported correctly than were any of the probes at distractor locations, includ- ing those between the targets. Together, these experiments provide strong converging evidence that when two targets are easily discriminated from distractors by a basic property, spatial attention can be split across both locations. Visual processing generally requires that important parts of the visual input be selected and processed more thoroughly than the rest. In many circumstances, the most important visual stimulus for a particular task will occupy a single undivided region of the visual field. In these cir- cumstances, selection can be accomplished effectively on the basis of location. In other words, all the information from one location is selected, and information from all other locations is excluded. Often, though, the important stimuli will occupy noncontiguous regions. For instance,