Abstract
Purpose: Selective attention can be employed to a restricted region in space or to specific objects. We have provided evidence that endogenously cued attention can be confined to a particular shape and location (VSS 2002). In the past, we also found that irrelevant stimuli interfered with the search task with location cueing but not with shape cueing. We hypothesize that this is due to the perceptual load of the task, cueing for shape being more attentionally demanding than cueing for location. We tested this idea by examining the effect of an irrelevant background on location cueing with two search tasks differing in difficulty. Methods: A feature search and a conjunction search involving relevant stimuli, one of which was the target, were presented either to the left or right of fixation, and were sometimes embedded among irrelevant background stimuli. The subject's task was to decide if the target was present (50%) or absent. A variable time before the stimuli, either a valid or invalid endogenous cue was given (an arrow pointing in the correct or incorrect location). Results: Valid cueing produced faster response times than invalid cueing. Response times were slower when the irrelevant stimuli were present. Most importantly, the irrelevant stimuli interfered more with the feature search task than with the conjunction search task. Conclusion: We concluded that with the easier feature search task, but not the conjunction task, some attentional resources remain available that allow irrelevant information to be processed, thus interfering with the search task.
Supported by NSERC and FCAR (MvG) and CNPq and Fapesp (CG)