Comparing the temporal dynamics and efficacy of task-relevant and task-irrelevant memory-driven attention.

People's attention is well attracted to a stimulus matching their memory. For example, when people are required to remember the color of a visual object, stimuli matching the memory color powerfully capture attention. Remarkably, stimuli with the shape of the memory object, that is, irrelevant-matching stimuli were also found to capture attention. Here, we examined how task relevance affects the temporal dynamics and the strength of memory-driven attention. In the experiment, participants performed a visual search task while maintaining the color or shape of a colored shape. When participants were required to memorize the color of the memory sample, the shape of the sample stimulus is task-irrelevant feature and vice versa. Importantly, while a search item matching working memory in the task-relevant dimension was presented for one group of participants, an irrelevant-matching search item appeared for the other group of participants. Further, we varied stimulus onset asynchrony (SOA) between the memory sample and search items. We found that relevant-matching stimuli captured attention regardless of whether the SOA was short or long. However, attentional capture by irrelevant-matching stimuli depended on the SOA; no memory-driven capture was observed at the shortest SOA, but significant capture was found at longer SOAs. Further, the capture effects by relevant-matching stimuli were greater than that of irrelevant-matching stimuli. These findings suggest both task-relevant and -irrelevant features in working memory affect the attentional selection in visual search task, but its temporal dynamics and strength are modulated by the task-relevance.