Covert and overt attention and the processing of cues for location and target identification

The authors compared covert and overt attention in a series of experiments designed to test some assumptions of space-based theories of visual attention. In Experiment 1, they measured reaction times (RTs) tc, a scaled letter presented at varied eccentricities. When the letter's location was cued in advance by a bar marker, identification responses were found to be similar across a 20 degrees area to the right and left of fixation. When related distracters were added to the display in Experiments 2 and 3, RTs were longer than in Experiment 1 and showed a U-shaped relationship with target and distracter distance. Only when the target letter appeared consistently in the center of the display was there evidence for a traditional spotlight with a unitary focus of attention. When both overt and covert attention conditions included multiple target locations, the data suggested that the distracter competed for attention and lengthened RTs in relationship to its distance from and compatibility with the target. The findings support an attentional mechanism that permits parallel access to noncontingent areas of the visual field.