Attentional Capture In Visual Search Research Articles

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

A recent study (Jung, Han, & Min, in press) reported that the extent to which attentional control is strained is a critical factor for observing stimulus-driven attentional capture in visual search. Expanding this study, we tested whether memory-driven attentional capture is also dependent on cognitive mechanism underlying visual search tasks. In our experiment, a group of participants performed a dual task, consisting of a working memory and a visual search task (memory-driven attention group), whereas the other performed only a visual search task (stimulus-driven attention group). Each group was further divided into two groups depending on the search task performed. For visual search tasks, we utilized two different search tasks; Landolt-C and orientation feature search tasks. For the former, participants searched for an outlined square with a top- or bottom-gap among left- or right-gap squares. For the latter, participants looked for a right- or left-tilted line among vertical lines. In a half of the total trials, a memory-matching/salient singleton distractor was present. In the remaining trials, no such a memory-matching/singleton distractor was present. As results, attentional capture by the singleton distractor was found under feature search task, p< .01. On the contrary, the task-irrelevant distractor did not capture when participants performed the Landolt-C search, p> .45. The memory-driven group showed a different pattern. A task-irrelevant, memory matching distractor captured attention when participants performed Landolt-C search task, p< .001. However, no memory-driven attentional capture was found under the feature search, p > .72. Our results demonstrate that the nature underlying visual search tasks is an important factor for observing both stimulus-driven and memory-driven attention. However, the specific patterns of the capture were opposite. These findings point to the role of interplay between the extent to which attentional control is strained and working memory in attentional capture.

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.

Attentional capture in visual search: Capture and post-capture dynamics revealed by EEG

Sometimes, salient-but-irrelevant objects (distractors) presented concurrently with a search target cannot be ignored and attention is involuntarily allocated towards the distractor first. Several studies have provided electrophysiological evidence for involuntary misallocations of attention towards a distractor, but much less is known about the mechanisms that are needed to overcome a misallocation and re-allocate attention towards the concurrently presented target. In our study, electrophysiological markers of attentional mechanisms indicate that (i) the distractor captures attention before the target is attended, (ii) a misallocation of attention is terminated actively (instead of attention fading passively), and (iii) the misallocation of attention towards a distractor delays the attention allocation towards the target (rather than just delaying some post-attentive process involved in response selection). This provides the most complete demonstration, to date, of the chain of attentional mechanisms that are evoked when attention is misguided and recovers from capture within a search display.

Priority of items in working memory affects attentional capture in visual search

Priority of items in working memory affects attentional capture in visual search

Effect of task set-modulating attentional capture depends on the distractor cost in visual search: evidence from N2pc.

Previous studies have confirmed that attention can be modulated by the current task set while involuntarily captured by salient items. However, little is known on which factors the modulation of attentional capture is dependent on when the same stimuli with different task sets are presented. In the present study, participants conducted two visual search tasks with the same search arrays by varying target and distractor settings (color singleton as target, onset singleton as distractor, named as color task, and vice versa). Ipsilateral and contralateral color distractors resulted in two different relative saliences in two tasks, respectively. Both reaction times (RTs) and N2-posterior-contralateral (N2pc) results showed that there was no difference between ipsilateral and contralateral color distractors in the onset task. However, both RTs and the latency of N2pc showed a delay to the ipsilateral onset distractor compared with the contralateral onset distractor. Moreover, the N2pc observed under the contralateral distractor condition in the color task was reversed, and its amplitude was attenuated. On the basis of these results, we proposed a parameter called distractor cost (DC), computed by subtracting RTs under the contralateral distractor condition from the ipsilateral condition. The results suggest that an enhanced DC might be related to the modification of N2pc in searching for the color target. Taken together, these findings provide evidence that the effect of task set-modulating attentional capture in visual search is related to the DC.

Neural correlates of reward-driven attentional capture in visual search

Event-related potentials (ERPs) were used to investigate whether a physically non-salient and task-irrelevant stimulus feature previously associated with reward can capture attention. In the training phase, participants implicitly associated a certain color with reward. In the subsequent test phase, participants searched for a uniquely shaped singleton among non-target shapes, with color completely irrelevant to the current task demand. Response time was delayed on trials wherein the target was simultaneously presented with an associated distracter, compared with trials without one. In ERPs, a lateralized reward-associated distracter elicited an N2pc component when a concurrent target was presented on the vertical meridian. The control experiment discounted the possibility that this N2pc was caused by familiarity of the reward-associated distracter. Presenting both the target and reward-associated distracter on the opposite side elicited N2pc, with the reward-associated distracter-elicited N2pc preceding the target-elicited N2pc, albeit only in trials with slow responses. These results show that the participants shifted their attention to the target only after noticing the task-irrelevant reward-associated distracter in slow trials. Therefore, task-irrelevant reward-driven salience can capture attention. Distracter positivity was observed in fast distracter-present trials presenting both a lateral distracter and a midline target. Thus, the reward-associated distracter should be actively suppressed to efficiently select the task-relevant target. Lastly, the distracter-elicited N2pc was negatively correlated with individual differences in reward drive score. This correlation may provide insight into reward sensitivity problems.

Multisensory enhancement of attentional capture in visual search

Multisensory integration increases the salience of sensory events and, therefore, possibly also their ability to capture attention in visual search. This was investigated in two experiments where spatially uninformative color change cues preceded visual search arrays with color-defined targets. Tones were presented synchronously with these cues on half of all trials. Spatial-cuing effects indicative of cue-triggered capture of attention were larger on tone-present than on tone-absent trials, demonstrating multisensory enhancements of attentional capture. Larger capture effects for audiovisual events were found when cues were color singletons, and also when they appeared among heterogeneous color distractors. Tone-induced increases of attentional capture were independent of color-specific top-down task sets, suggesting that this multisensory effect is a stimulus-driven bottom-up phenomenon.

The effect of motion onset and motion quality on attentional capture in visual search

The effect of motion onset and motion quality on attentional capture in visual search

Top-down search strategies determine attentional capture in visual search: Behavioral and electrophysiological evidence

To investigate how attentional capture in visual search is affected by generalized top-down search strategies, ERPs and behavioral performance were measured in two experiments where spatially nonpredictive color singleton cues preceded visual search arrays that contained one of two equally likely color singletons. When both singletons served as targets, irrelevant-color singleton cues produced behavioral attentional capture effects and elicited an N2pc component, indicative of a singleton search mode. When responses were required to only one of the two color singletons, the same cues no longer elicited behavioral spatial cuing effects, and the N2pc to these cues was attenuated and delayed, in line with the hypothesis that search was now guided by a feature-specific search strategy. Results demonstrate that the ability of visual singleton stimuli to capture attention is not simply determined by their bottom-up salience, but strongly modulated by top-down task sets.

Driven to less distraction: rTMS of the right parietal cortex reduces attentional capture in visual search by eliminating inter-trial priming

Driven to less distraction: rTMS of the right parietal cortex reduces attentional capture in visual search by eliminating inter-trial priming

Driven to Less Distraction: rTMS of the Right Parietal Cortex Reduces Attentional Capture in Visual Search

In visual search, the presence of a highly salient color singleton can slow or facilitate search for a shape target depending on whether the singleton is a distractor or coincides with the target. This is consistent with an attentional shift (attentional capture) to the salient item. This attentional capture can be driven by bottom-up or top-down processes or both. We investigated the role of the parietal cortex in attentional capture by a singleton using repetitive transcranial magnetic stimulation. Following disruption to the right posterior parietal cortex by sustained transcranial magnetic stimulation, the reaction time (RT) cost of the singleton distractor was reduced. At least part of this lessening of singleton distraction was due to the elimination of priming (top-down) effects between target and distractor singletons on consecutive trials. In Experiment 2, we presented the different conditions in separate blocks meaning any effects of the distractor can most likely be attributed to bottom-up processes. Nevertheless, there was still a decrease in RT interference from the distractor so that a reduction in priming cannot provide a full account of the results. The data are consistent with previous work positing that the right parietal cortex directs attention to salient stimuli (e.g., Constantinidis 2005, Mevorach et al. 2006), while also suggesting a role for the right parietal cortex in the integration of bottom-up salience information with memories for salient features on prior trials.

Frontal control of attentional capture in visual search

Lavie and colleagues recently suggested that cognitive control functions that are mediated by frontal cortex provide goal-directed control of selective attention, serving to minimize interference by goal-irrelevant distractors. Here we provide new evidence for this claim from an attentional capture paradigm. An event-related fMRI experiment shows that the presence (vs. absence) of an irrelevant colour singleton distractor in a visual search task was not only associated with activity in superior parietal cortex, in line with a psychological attentional capture account, but was also associated with frontal cortex activity. Moreover, behavioural interference by the singleton was negatively correlated with frontal activity, suggesting that frontal cortex is involved in control of singleton interference. Behavioural tests confirmed that singleton interference depends on availability of cognitive control to the search task: Singleton interference was significantly increased by high working memory load. These results demonstrate the important role of frontal cognitive control of attention by working memory in minimizing distraction.

Selectivity in distraction by irrelevant featural singletons: evidence for two forms of attentional capture.

Four experiments addressed the degree of top-down control over attentional capture in visual search for featural singletons. In a modified spatial cuing paradigm, the spatial relationship and featural similarity of target and distractor singletons were systematically varied. Contrary to previous studies, all 4 experiments showed that when searching for a singleton target, an irrelevant featural singleton captures spatial attention only when defined by the same feature value as the target. Experiments 2, 3 and 4 provided a potential explanation for the discrepancy with previous studies by showing that irrelevant singletons can produce distraction effects that are dissociable from shifts of spatial attention. The results suggest the existence of 2 distinct forms of attentional capture.