Effects of abruptly appearing clutter on a peripherally precued covert attention shift.

The effects of clutter that appears abruptly with the target during covert shifts of attention to a precued target location in the visual field were studied. The delay between the appearance of the precue and that of the target with clutter was varied within each block. Blocked conditions included clutter density, the similarity between the shape of the clutter character and that of the target, and whether a clutter character appeared in each path between fixation and the target. Also, a no-clutter control condition was run in this totally within-subject design. Implications of the results for early versus late-selection models of attention were assessed.