Abstract
It is widely agreed that encoding information into working memory (WM) depends on attention allocation processes. We examined the hypothesis that the temporal dynamics of attentional engagement determine the outcome of WM encoding in RSVP tasks. We employed a task where two lateralized streams containing letters and digits appeared in rapid succession. A target object was closely followed by a (post-target) distractor that shared the target’s response dimension, such that participants often erroneously report its identity. In a series of three experiments, the speed of attentional engagement was tracked by measuring N2pc components, separately for trials where participants correctly identified the target and intrusion trials where participants reported the digit that followed the target. Across experiments, the onset of the target-locked N2pc was correlated with the speed the target-defining feature was detected. Within each experiment, intrusions were associated with later target-locked N2pc onsets relative to correct trials. Thus, these experiments showed that distractor intrusions occur when attentional engagement is slow and enhances the distractor instead of the target. In a second series of experiments, we examined the fate of the target on trials where participants committed distractor intrusions. When participants were given the opportunity to provide two distinct responses, intrusions were followed by above-chance target identification. When the post-target distractor was excluded as a possible response, accuracy improved but was below baseline performance. A final experiment revealed that the presence of the distractor did not affect the representational quality of the target, but instead blocked WM encoding on part of trials. Together, these findings suggest the existence of a mechanism in which perceptual information is accumulated and compared to the attentional set prior to attentional engagement. This mechanism introduces variability in the speed of attentional engagement that affects feature activation, which in turn determines WM encoding and perceptual reports.