PD components and distractor inhibition in visual search: new evidence for the Signal Suppression Hypothesis

The hypothesis that salient distractors in visual search are actively suppressed is supported by the fact that these objects elicit PD components believed to be associated with inhibition. This account was challenged by Kerzel and Burra (2020), who found that a PD to lateral colour singleton distractors was followed by a contralateral negativity, which they interpreted as an N2pc indicative of attentional capture. As this would be at odds with successful distractor suppression, they proposed an alternative lateral-first serial scanning hypothesis, which assumes that the PD might actually be an N2pc elicited when a lateral context item is selected. We tested this hypothesis by measuring lateralized ERP components to search displays with two lateral and two vertical midline items, including a colour singleton and a shape-defined target. Colour singletons triggered PD components not only in blocks where attention was unfocused because target location was unpredictable, but critically also in blocks where targets only appeared on the midline and participants had no reason to attend to lateral items. This is inconsistent with the serial scanning hypothesis and supports the idea that the PD reflects signal suppression. PD components to singleton distractors were followed by a contralateral negativity, which we interpreted as a second PD elicited by non-salient distractors on the opposite side. Our sequential inhibition account reconciles conflicting results of recent studies and emphasizes the role of inhibitory processes during attentional target selection in visual search