Abstract: The current study investigated the interaction between the perceptual load in searching for a target and the distance between the target and a task-irrelevant singleton in regulating stimulus-driven attentional capture. Participants were asked to search for a target letter among nontarget letters and were instructed to ignore a differently colored task-irrelevant singleton letter, which was compatible, neutral or incompatible with the response to the target letter. The perceptual load of the search display was low (with set size of 4), medium (with set size of 8) or high (with set size of 12). The target and the task-irrelevant singleton were close to or distant from each other. Results showed that the flanker interference effect, in terms of the reaction times (RTs) in neutral condition subtracted from that in incompatible condition, was significant for the low perceptual load condition, but was reduced for the medium and the high load conditions. Moreover, for the medium and the high load conditions, the flanker effect was significantly larger when the target and the task-irrelevant singleton were distant from each other than when they were close to each other. The flanker effect thus was affected by both the perceptual load of the search display and the distance between the target and the task-irrelevant singleton. These results indicate that whether the task-irrelevant singleton captures attention and causes interference with the current target processing is not only affected by whether there are overall spare attentional resources left from processing the current task, but is also affected by whether there are spare attentional resources at the subregion where the singleton is located.

Key words: perceptual load, attentional capture, singleton, localized attentional interference, attentional resource