Suk Won Han

Do the Contents of Working Memory Capture Attention? Yes, but Cognitive Control Matters.

There has been a controversy on whether working memory can guide attentional selection. Some researchers have reported that the contents of working memory guide attention automatically in visual search (D. Soto, D. Heinke, G. W. Humphreys, & M. J. Blanco, 2005). On the other hand, G.F. Woodman and S. J. Luck (2007) reported that they could not find any evidence of attentional capture by working memory. In the present study, we tried to find an integrative explanation for the different sets of results. We report evidence for attentional capture by working memory, but this effect was eliminated when search was perceptually demanding or the onset of the search was delayed long enough for cognitive control of search to be implemented under particular conditions. We suggest that perceptual difficulty and the time course of cognitive control as important factors that determine when information in working memory influences attention.

Functional Fractionation of the Stimulus-Driven Attention Network

A novel, salient event in the environment powerfully captures attention. This stimulus-driven attentional capture not only includes orienting of attention toward the event, but also an evaluative process to determine the behavioral significance and appropriate response to the event. Whereas a network of human brain regions composed of prefrontal and temporoparietal regions have been associated with stimulus-driven attention, the neural substrates of orienting have never been teased apart from those of evaluative processes. Here we used fMRI to measure the human brains response to the temporally extended presentations of salient, task-irrelevant stimuli, and found a clear functional dissociation in the stimulus-driven attention network; the anterior insula and cingulate cortex showed transient orienting responses to the onsets and offsets of the stimuli, whereas the temporoparietal cortex exhibited sustained activity throughout event evaluation. The lateral prefrontal cortex was implicated in both attentional and evaluative processes, pointing to its central, integrative role in stimulus-driven attention.

The source of dual-task limitations: serial or parallel processing of multiple response selections?

Although it is generally recognized that the concurrent performance of two tasks incurs costs, the sources of these dual-task costs remain controversial. The serial bottleneck model suggests that serial postponement of task performance in dual-task conditions results from a central stage of response selection that can only process one task at a time. Cognitive-control models, by contrast, propose that multiple response selections can proceed in parallel, but that serial processing of task performance is predominantly adopted because its processing efficiency is higher than that of parallel processing. In the present study, we empirically tested this proposition by examining whether parallel processing would occur when it was more efficient and financially rewarded. The results indicated that even when parallel processing was more efficient and was incentivized by financial reward, participants still failed to process tasks in parallel. We conclude that central information processing is limited by a serial bottleneck.

Spatial working memory load impairs signal enhancement, but not attentional orienting

The present study examined the effect of spatial working memory load on the attentional cuing effect. It is well-known that spatial working memory and spatial attention functionally overlap or share a common resource. Given this functional overlapping, it is possible that spatial working memory would also interact with the attentional cuing effect. Considering the distinction between channel selection and channel enhancement by attention (Prinzmetal, McCool, & Park, 2005), we expected that the interaction between spatial working memory and the cuing effect would differ with attentional processing type. Two experiments conducted with the spatial cuing paradigm showed that the magnitude of the cuing effect as measured by reaction time, reflecting channel selection, was uninfluenced by spatial working memory load. In contrast, spatial working memory load reduced the cuing effect as measured by accuracy, reflecting channel enhancement. These results suggest that spatial working memory load impairs signal enhancement by attention and does not influence attentional orienting per se. The interaction between spatial working memory and visual perception is also discussed.

The effects of stimulus-driven competition and task set on involuntary attention

It is well established that involuntary attention—the exogenous capture of attention by salient but task-irrelevant stimuli—can strongly modulate target detection and discrimination performance. There is an ongoing debate, however, about how involuntary attention affects target performance. Some studies suggest that it results from enhanced perception of the target, whereas others indicate instead that it affects decisional stages of information processing. From a review of these studies, we hypothesized that the presence of distractors and task sets are key factors in determining the effect of involuntary attention on target perception. Consistent with this hypothesis, here we found that noninformative cues summoning involuntary attention affected perceptual identification of a target when distractors were present. This cuing effect could not be attributed to reduced target location uncertainty or decision bias. The only condition under which involuntary attention improved target perception in the absence of distractors occurred when observers did not adopt a task set to focus attention on the target location. We conclude that the perceptual effects of involuntary attention depend on distractor interference and the adoption of a task set to resolve such stimulus competition.

Dissociation between process-based and data-based limitations for conscious perception in the human brain.

Successful performance of a cognitive task depends upon both the quality of the sensory information and the processing resources available to perform that task. Thus, task performance can either be data-limited or process-limited (D. A. Norman and D. G. Bobrow, 1975). Using fMRI, we show that these conceptual distinctions are neurally dissociable: A parieto-frontal network involved in conscious perception is modulated by target interference manipulations that strain attentional processing, but not by equally difficult manipulations that limit the quality of target information. These results suggest that limitations imposed by processing capacity have distinct neural effects from those arising from the quality of sensory input, and provide empirical support for an influential neurobiological theory of consciousness (S. Dehaene, J.-P. Changeux, L. Naccache, J. Sackur, and C. Sergent, 2006).

Search efficiency is not sufficient: The nature of search modulates stimulus-driven attention

It has long been debated whether or not a salient stimulus automatically attracts people’s attention in visual search. Recent findings showed that a salient stimulus is likely to capture attention especially when the search process was inefficient due to high levels of competition between the target and distractors. Expanding these studies, the present study proposes that a specific nature of visual search, as well as search efficiency, determines whether or not a salient, task-irrelevant singleton stimulus captures attention. To test this proposition, we conducted three experiments, in which participants performed two visual search tasks whose underlying mechanisms are known to be different: orientation-feature search and Landolt-C search tasks. We found that color singleton distractors captured attention when participants performed the orientation-feature search task. The magnitude of this capture effect increased as search efficiency decreased. On the contrary, the capture by singleton distractors was not observed under the Landolt-C search task. This differential pattern of capture effect was not due to differences in search efficiency across the search tasks; even when search efficiency was controlled for, stimulus-driven capture of attention by a salient distractor was found only under the feature search. Based on these results, the present study suggests that in addition to search efficiency, the nature of search strategy and the extent to which attentional control is strained play crucial roles in observing stimulus-driven attentional capture in visual search.