Can multiple equally salient distractors be suppressed simultaneously?

While unique salient items tend to “pop out” from a visual scene, capturing our attention, there is a growing body of research suggesting that task-irrelevant salient items can instead be suppressed. Previous research has primarily focused on the suppression of one salient item. Using behavioural and electrophysiological (PD component) measures, we recently showed that, for displays with two salient items, suppression was stronger for the more salient item (Drisdelle & Eimer, 2023). Here, we compared displays with one salient item and two salient items using behavioural (Experiment 1) and electrophysiological (Experiment 2) measures. In both tasks, participants searched for a shape-defined target among target-coloured distractors and zero (Experiment 1 only), one, or two different-coloured (salient) distractors. Salient distractors were always the same colour. Experiment 1 employed a capture-probe paradigm, where participants reported probe letters superimposed on all shapes. Critically, suppression effects (an impaired ability to report letters at a salient distractor location) were equally strong regardless of whether another salient distractor was present, indicating efficient multiple-item suppression. Experiment 2 provided converging electrophysiological evidence, based on PD components (ERP markers of suppression) elicited by displays with one or two lateral salient distractors. Lateralised distractor related activity was isolated from target related activity by only examining displays where the target was absent or on the midline. Critically, the PD elicited by displays with two lateral salient distractors was significantly larger than the PD elicited by displays with a single lateral salient distractor. This indicated that PD components can reflect the combined contribution of suppression that is applied simultaneously to multiple salient distractors. Taken together, our results suggest that it is possible to suppress multiple distractor items that are equally salient, and that this suppression does not result in any behavioural costs relative to single-item suppression.