Attentional Capture by Working Memory Contents

Article excerpt

There has been controversy on whether working memory (WM) contents automatically guide attention. The present study tried to replicate the effect of WM-based attentional capture using an adaption of Downing's (2000) paradigm, in which WM and attentional capture were combined. Subjects were presented with an attention display containing two objects, one of which could be precued by a matching item being held in WM. As measured by a probe discrimination task, the memory-matching object had a privileged status to capture attention regardless of the stimulus onset asynchronies between the memory cue and the attention display, even when there was absolutely no benefit for subjects to bias attention in favour of the memory match. These results suggest that WM contents guide attention in an involuntary manner. The implications of current findings for understanding of WM effects on visual selection are discussed.

Keywords: working memory, attentional capture, automaticity

Because there are usually much more stimuli in the scene than the limited capacity visual system can process at any moment, visual attention selects only a minority of them for further processing. Many models of attention in visual search suggest that working memory (WM) contents play an important role in the guidance of visual attention (e.g., Bundesen, 1990; Desimone & Duncan, 1995; Duncan & Humphreys, 1989; Wolfe, 1994). The target template held in WM serves to bias attention in a top-down manner to process target-like objects in the visual scene. Singleunit recording studies provide the strongest evidence for the maintenance of target template in WM and its key role in the guidance of attention during visual search (e.g., Chelazzi, Miller, Duncan, & Desimone, 1993, 2001). For example, Chelazzi et al. (1993) recorded neural activity in the temporal lobe of monkeys while they performed a delayed match-to-sample task. Chelazzi et al. found that the neurons coded for the target maintained an elevated firing rate during the delay interval. This was interpreted as evidence that the target template was being actively held in WM during the retention interval. Also, the target template provides a bias signal to the neurons that perform perceptual analysis, inducing a competitive advantage for neurons that selectively respond to the target.

Items held in WM should be deliberately used by observers to bias the allocation of attention when they are related to the target of the task at hand. However, what will happen when the memory items match the task-irrelevant stimuli (memory-matching distractors)? Do the memory-matching distractors involuntarily capture attention? Previous studies testing effects of WM on attention have reported contradictory findings. Some researchers have reported that the contents of WM guided attention in an involuntary fashion (e.g., Downing, 2000; Soto, Heinke, Humphreys, & Blanco, 2005). On the other hand, Woodman and Luck (2007) argued that WM did not automatically guide attention, but rather, WM contents could be used in a flexible manner according to their relationship with the search task at hand. The present study aimed to replicate the automatic effect of WM on visual selection using a task paradigm similar to that used by Downing (2000).

In the first experiment of Downing's (2000) study, participants were shown a face at the beginning of each trial and were instructed to hold it in WM throughout the trial. After the offset of the memory face, two prime faces were simultaneously presented, one of which matched the memory face and the other novel. This was followed by a probe briefly presented at the location of one of the previous prime faces. The results showed that performance was faster to the probe at the location of the memory-matching face than to the probe at the location of the nonmatching face. Since participants were told that the two prime faces were task irrelevant, Downing suggested that this pattern of results reflected the automatic guidance of visual spatial attention from WM. …