Salience-based integration of redundant signals in visual pop-out search: evidence from behavioral and electrophysiological measures

Behavioral and electrophysiological evidence is presented suggesting that, in visual search for feature singleton targets, multidimensional signals are integrated at a preselective stage of processing. Observers searched for a target that was consistently defined by the same features, but differed from the variable context either nonredundantly by one or redundantly by two dimensionally different features. The behavioral results showed reaction time redundancy gains and evidence of coactive processing, and the electrophysiological analyses revealed the latency of the N2pc component of the event-related potential (ERP) to be expedited by redundant relative to nonredundant displays, while the response-related lateralized readiness potential (LRP) remained unaffected. These findings suggest that target signal integration in singleton search paradigms occurs pre-attentively, that is, prior to focal-attentional target selection, with observers basing their responses on the detection of featureless saliency signals, even under conditions in which the target features remain constant and are known in advance. These results have implications for theories assuming top-down influences in feature detection.