Opposing effects of stimulus-driven and memory-driven attention in visual search.

When one searches for a specific target in a cluttered visual scene, a perceptually salient stimulus or a stimulus that matches working memory's contents is prioritized for attentional selection. In the present study, we aimed at clarifying under which circumstance stimulus-driven attention or memory-driven attention is more pronounced. We hypothesized that one crucial factor affecting stimulus-driven versus memory-driven attention is how a concurrent visual search task is performed. To address this issue, we employed two visual search tasks whose underlying mechanisms are known to be different: Landolt-C search and orientation feature search. One group of participants performed visual search tasks containing a memory-matching stimulus, and the other group conducted searches in the presence of a salient singleton distractor. The results showed that the effects of stimulus-driven and memory-driven attention differed, depending on the cognitive mechanisms underlying the visual search tasks. A memory-matching stimulus captured attention when participants performed the Landolt-C search, whereas this capture was diminished under feature search. In contrast, capture by the salient singleton distractor was found only under feature search. These results demonstrate that the nature of the underlying visual search tasks is an important factor for observing stimulus-driven versus memory-driven attention. Our results also provide a potential solution to resolve current debate regarding memory-driven attention in visual search.