Ideally, both enhancement of relevant and suppression of irrelevant information contribute to the deployment of visual selective attention. When stimuli are sufficiently salient, however, they can capture attention automatically before they are suppressed and thus interfere with the selection relevant stimuli. Here we analyzed how much interference is induced by distractors of varying distance to a target stimulus and how the visual system responds to that interference. We used an additional singleton visual search task in which participants had to search for a target and ignore a salient distractor presented at different distances to the target. We found behavioral evidence for spatial filtering costs: distractor interference increased with distractor proximity to the target, distractor interference was reduced when the target and distractor spatially coincided, and responses were slowed down when distractor and target were incompatible. Event-related potentials of the EEG paralleled this pattern: N2pc amplitude (reflecting target enhancement) increased while Pd amplitude (reflecting distractor suppression) decreased as the distance increased between target and distractor. This suggests less efficient enhancement of relevant and more effortful suppression of irrelevant information when target and singleton are closer, in line with the idea of increased neural competition for stimuli within the same receptive field. Distractors elicited an N2pc that was not affected by target-distractor distance, suggesting that varying attentional capture does not contribute to filtering costs. Importantly, when the distractor was presented in the same position as the target, we observed robust interference relative to a no-distractor condition. This evidence against a pure-capture account and suggests nonspatial interference contributes to the overall increased processing time when salient stimuli are presented. We additionally applied an inverted encoding model to track attentional subprocesses in a more fine-grained manner. Alpha-band topography tracked sustained top-down attention deployment towards targets, and transient but more pronounced attentional capture by the distractor. Below-baseline channel activity for distractors in the theta-band topography of the EEG signal tracked spatial suppression. In sum, our results show that salient distractors induce both spatial and nonspatial interference and that the visual system responds with a gradient of suppression that can account for distance-variant processing costs.
bioRxiv Subject Collection: Neuroscience