Redundancy gains in pop-out visual search are determined by top-down task set: behavioral and electrophysiological evidence.

We combined behavioral and electrophysiological measures to find out whether redundancy gain effects in pop-out visual search are exclusively determined by bottom-up salience or are modulated by top-down task search goals. Search arrays contained feature singletons that could be defined in a single dimension (color or shape) or redundantly in both dimensions. In the baseline condition, both color and shape were task-relevant, and behavioral redundancy gain effects were accompanied by an earlier onset of the N2pc component for redundant as compared to single-dimension targets. This demonstrates that redundancy gains are generated at an early visual-perceptual level of processing. In the color target and shape target conditions, only one dimension was task-relevant, while the other could be ignored. In these two conditions, behavioral and electrophysiological redundancy gains were eliminated. We conclude that redundant-signals effects in pop-out visual search are not driven by bottom-up salience but are instead strongly dependent on top-down task set.