Visual search for singleton feature targets across dimensions:: Stimulus and expectancy-driven effects in dimensional weighting

Four pop-out search experiments investigated whether dimension-based visual attention is top-down modulable. Observers searched for singleton feature targets defined, variably across trials, by a color or an orientation difference to nontargets. Observers were precued to the most probable target-defining dimension (e.g., by the word color) or feature (red) on a given trial. Results revealed expedited reaction times (RTs) for valid-dimension targets relative to neutral-cue conditions, and slowed RTs for invalid-dimension targets. Cue information as to precise target feature yielded some extra effect only for color targets. The dimensional cuing significantly reduced, but did not abolish, the dimension-specific influence of the previous target on detection of the current target (same-dimension RT < differentdimension RT). These findings confirm that top-down dimensional set modulates stimulus-driven processes in the detection of pop-out signals.