Journal of Experimental Psychology: Human Perception and Performance 2014, Vol. 40, No. 4, 1301-1307
© 2014 American Psychological Association 0096-1523/14/S12.00 http://dx.doi.org/10.1037/a0036451
OBSERVATION
Role of Attentional Tags in Working Memory-Driven Attentional Capture Chun-Yu Kuo
Hsuan-Fu Chao
National Taiwan University
Chung Yuan Christian University
Recent studies have demonstrated that the contents of working memory capture attention when perform ing a visual search task. However, it remains an intriguing and unresolved question whether all kinds of items stored in working memory capture attention. The present study investigated this issue by manip ulating the attentional tags (target or distractor) associated with information maintained in working memory. The results showed that working memory-driven attentional capture is a flexible process, and that attentional tags associated with items stored in working memory do modulate attentional capture. When items were tagged as a target, they automatically captured attention; however, when items were tagged as a distractor, attentional capture was reduced. Keywords: working memory, attentional tag, attentional capture
Over the last decade, numerous studies have been published showing that the contents of working memory can capture atten tion (e.g., Downing, 2000; Han & Kim, 2009; Houtkamp & Roelfsema, 2006; Kuo, Chao, & Yeh, 2013; Olivers, Meijer, & Theeuwes, 2006; Soto, Heinke, Humphreys, & Blanco, 2005; Soto, Hodsoll, Rotshtein, & Humphreys, 2008; Woodman & Luck, 2007). This is usually demonstrated by combining a working memory task with a visual search task. At the beginning of a trial, participants are instructed to remember an item for a memory test they will be given at the end of the trial. Between the study phase and the memory test, participants perform a separate visual search task. The critical finding is that although the memorized item is unrelated to the visual search task, it still captures the participants’ attention. For instance, when the memorized item and another item were presented simultaneously as uninformative cues before the onset of the visual search display, participants responded faster when the target was presented in the same location as where the memorized item had been (Downing, 2000). In addition, visual search was faster when the target was presented in a shape that matched the item held in working memory, whereas responses were slower when the distractor was presented in the shape of the memorized item (Soto et al., 2005). Olivers et al. (2006) also demonstrated that a singleton distractor produces more interfer ence when its color matches that of the memorized item.
The literature clearly supports the idea of working memorydriven attentional capture. However, it remains less clear whether all kinds of items held in working memory capture attention in the same manner. More specifically, in complex environments in daily life, we not only remember the people, objects, and events we wish to pay attention to, but also the stimuli to which we do not wish to attend to. The ability to distinguish between what we do and do not want to pay attention to is vital for efficient performance and overall well-being (Lee & Chao, 2012). To achieve this, items we wish to attend to may be tagged with a “target tag” in working memory, whereas those we choose to ignore are given a “distractor tag.” Stimuli matching the target items held in working memory should be attended to, whereas we should inhibit responses to stimuli matching the distractor items, disengaging our attention from them. Although there is ample evidence that the contents of working memory can capture our attention, the effect of target and distractor tags in working memory is yet to be determined. In previous studies investigating working memory-driven atten tional capture, participants were required to memorize items for a later recognition task. In this situation, the memorized items must be tagged as targets for the up-coming recognition task. In con trast, the role of distractor tags in working memory is not clear. Demonstrations of active inhibition (Chao, 2010, 2011) may pro vide indirect evidence for the existence of distractor tags in work ing memory. Chao demonstrated that when participants know the location or identity of the forthcoming distractor, responses to the target are faster than when people do not have information about the distractor in advance. In addition, effects of distractor precuing are reduced or even eliminated under high working memory load. Hence, it is possible that active inhibition of attention to a distrac tor occurs when the stimulus is deliberately allocated a distractor tag in working memory. Arita, Carlisle, and Woodman (2012) also showed that visual search was improved when a distractor was precued, implying that a distractor template in working memory can bias attention away from a stimulus matching that item.
This article was published Online First April 14, 2014. Chun-Yu Kuo, Department of Psychology, National Taiwan University, Taipei, Taiwan; Hsuan-Fu Chao, Department of Psychology, Chung Yuan Christian University, Chung Li, Taiwan. This work was supported by a grant from the National Science Council of Taiwan to Hsuan-Fu Chao, (NSC 99-2410-H-033-024-MY3). Correspondence concerning this article should be addressed to Hsuan-Fu Chao, Department of Psychology, Chung Yuan Christian University, No. 200, Chung Pei Road, Chung Li 32023, Taiwan. E-mail: hfchao@ cycu.edu.tw 1301
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In the current study, we systematically investigated whether items stored in working memory for different task goals influenced working memory-driven attentional capture. To this end, partici pants were required to memorize a color for a memory task at the end of each trial. In one block, the memorized color indicated what would be the target; in the other block, the memorized color signified the distractor. In both cases, the information had to be held in working memory while completing a separate motion discrimination or orientation discrimination task. If the contents of working memory capture attention regardless of the attentional tags assigned to them, working memory-driven attentional capture will be observed in both conditions. Conversely, if these tags play an important role in attention allocation, attentional capture will only be observed when the item held in working memory is associated with the target tag.
all items stored in working memory capturing attention regardless of the nature of the tag. Second, it is possible that the visual system works to inhibit attentional capture to stimuli matching items associated with a distractor tag.
Method Participants. Thirty-four undergraduate students from the National Taiwan University participated in this experiment for either course credit or NTS 100. All participants had normal or corrected-to-normal vision. Procedure. We modified Downing’s (2000) paradigm to ex amine how the information maintained in working memory for a different task influences motion discrimination in various contexts. Figure 1A shows the sequence of events in a trial. Each trial began with a fixation point presented for 500 ms. A colored circle was then presented at the center of the screen for 1,000 ms, and participants were instructed to memorize the color for a memory task at the end of each trial. A fixation point was then presented for 1,500 ms. Next, two colored circles were presented for the motion discrimination task, one on either side of the fixation point, for 187 ms. Then, one of the colored circles moved either upward or downward by 0.5 degrees. After 53 ms, the two colored circles disappeared and a question mark appeared, indicating that partic ipants should enter the motion direction (up or down) of the moving circle. After responding, two new colored circles (one of which matched the memorized color) were presented for the mem ory task, each with a notch on either the top or the bottom. Participants were required to search for the circle that matched (target-tag block) or mismatched (distractor-tag block) the mem orized color, and indicate whether the circle had a notch in its top or bottom.
Experiment 1 Experiment 1 was conducted to examine whether different tags in working memory have different effects on attention allocation. We modified Downing’s (2000) paradigm by combining a motion discrimination task and a memory task. The critical manipulation was whether the item stored in working memory was the target or distractor for the memory task. It should be noted that the items held in working memory and the target or distractor tags associated with each item were unre lated to the demands of the motion discrimination task. However, if these items still modulated performance in the motion discrim ination task, then the effect would be seen as involuntary. In addition, we were particularly interested in the mechanism involved in processing distractor tags. There are at least two possibilities in this regard. First, it is possible that the distractor tag has no effect on working memory-driven attentional capture, with
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Figure 1. The trial sequences in Experiments 1 to 4. Figure 1A is an example of an invalid trial in which the memorized prime was the distractor in the motion discrimination task in Experiments 1 and 2. Figure IB is an example of an invalid trial in which the memorized prime was the target in the orientation discrimination task in Experiment 3. Figure 1C is an example of an invalid trial in which the memorized prime was the distractor in the motion discrimination task in Experiment 4.
ROLE OF ATTENTIONAL TAGS
In half of all trials, the memorized item matched the distractor in the motion discrimination task (invalid condition); in the other half of the trials, the memorized color was not presented in the motion discrimination task (neutral condition). The trials were blocked by tag type, with each block containing 64 trials of either target- or distractor-tag conditions. There were two blocks each of target- and distractor-tag block, resulting in a total of four blocks. The target- and distractor-tag blocks were alternated and counter balanced, such that half of the participants started with target- and the other half started with distractor-tag block. The total number of experimental trials was 128, each experimental condition consist ing of 32 trials.
Results and Discussion Accuracy was at ceiling in both the motion discrimination task (99%) and the memory task (98%). Reaction time (RT) data from the motion discrimination task for trials where both motion dis crimination and memory recognition were correct were analyzed. Trials with RTs longer than 1,800 ms or shorter than 70 ms were excluded. Figure 2 shows the RTs in the motion discrimination task. A 2 (tag type: target tag or distractor tag) X 2 (trial type: invalid or neutral) repeated measures analysis of variance (ANOVA) on motion discrimination RTs showed that the main effect of trial type was significant, F (l, 33) = 9.08, p = .005, tip = .22. In addition, there was a significant interaction between tag type and trial type on RT, F (l, 33) = 9.38, p = .004, ^ = .22. Further analysis showed that performance was faster in the neutral condi tion than in the invalid condition in the target-tag block, F (l, 66) = 18.31, p < .001, r\2p = .22; but there was no difference between neutral and invalid condition in the distractor-tag block, F (l, 66) = 0.10, p = .75, ^p = .002. The main effect of tag type was not significant, F (l, 33) = 0.21, p > .10, rip = .006. Experiment 1 demonstrated the impact of attentional tags on working memory-driven attentional capture. Stimuli matching memorized items associated with target tags were more likely to
Tag T yp e
Figure 2. Mean correct response times (RTs) in the selection task as a function of trial type and tag type in Experiment 1. Error bars represent SEs. The black bars show the performance in the invalid condition, and the dark gray bars depict the performance in the neutral condition.
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capture attention than stimuli given distractor tags. This suggests that attentional capture by items tagged as distractors may be inhibited.
Experiment 2 Experiment 1 showed that there was no working memory-driven attentional capture when the items stored in working memory were associated with a distractor tag. However, because the memorized item was never the target in the motion discrimination task, and given that previous studies have had difficulty observing the effect of attentional capture in this type of situation (Woodman & Luck, 2007), it remained a question whether the findings of Experiment 1 was a special case. Hence, Experiment 2 was aimed at replicating the findings of Experiment 1 with the inclusion of valid trials, in which the target in the motion discrimination task matched the item held in working memory. We hypothesized that the contents of working memory would capture attention when they were associated with a target tag, and that in the valid condition, the responses would be faster than those in the neutral condition. Conversely, the benefit in the valid condition should be reduced when the item stored in working memory was associated with a distractor tag.
Method Participants. Twenty-six undergraduate participants from the National Taiwan University participated in Experiment 2 for either course credit or NT$100. All participants had normal or correctedto-normal vision. Procedure. All aspects of Experiment 2 were identical to Experiment 1, with two exceptions. In Experiment 2, three kinds of Uials (invalid, neutral, and valid) were presented with equal fre quency in random order. There were also now 24 trials in each condition, for a total of 144 experimental trials.
Results and Discussion Accuracy was at ceiling in both the motion discrimination task (98%) and the memory task (96%). Figure 3 shows the RTs in the motion discrimination task. A repeated measures ANOVA for RTs on the motion discrimination task revealed that the main effect of trial type was again significant, F(2, 50) = 7.02, p = .002, = .22. Performance was slower in the invalid condition than that of both the neutral (p < .01) and valid condition {p < .05). In addition, there was a significant interaction between tag type and trial type, F(2, 50) = 5.34, p = .008, i)2 = .18. This interaction arose because the effect of trial type was significant in the targettag block, F(2, 100) = 10.32, p < .001, tip = .17, but not in the distractor-tag block, F(2, 100) = 1.95, p = .19, rip = .04. The performance in the target-tag block was slower in the invalid condition than in the neutral and valid conditions {p < .01). The difference between the valid and neutral conditions was not sig nificant {p > .10). The main effect of tag type was not significant, F (l, 25) = 2.91, p > .10, T|p = .10. Experiment 2 replicated the major findings of Experiment 1: the contents of working memory captured attention when they were associated with a target tag, but not when they were associated with a distractor tag. It should be noted that although there was a
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Results and Discussion
Tag T y p e
Figure 3. Mean correct response times (RTs) in the selection task as a function of trial type and tag type in Experiment 2. Error bars represent SEs. The black bars show the performance in the invalid condition, the dark gray bars show the performance in the neutral condition, and the light gray bars depict performance in the valid condition.
trend of a response benefit (17 ms) in the valid condition when the items stored in working memory were associated with a target tag, this did not reach significance. Thus, the following experiments were conducted using the valid condition to examine whether there is a specific response benefit to stimuli matching the contents of working memory with the target tag.
Experiment 3 Experiment 3 aimed to test the generality of the results from Experiments 1 and 2. Although the motion discrimination task used in Experiments 1 and 2 has been used in several studies on working memory-driven attention capture (e.g., Downing, 2000; Kuo et al., 2013), the orientation discrimination task has also successfully been used to measure this effect (e.g., Soto et ah, 2005; Soto & Humphreys, 2007). Hence, we used the orientation discrimination task in Experiment 3 to replicate Experiments 1 and 2.
Accuracy was at ceiling in both the orientation discrimination task (99%) and the recognition task (98%). Figure 4 shows the RTs for the orientation discrimination task. A repeated measures ANOVA for orientation discrimination RTs revealed that the main effect of trial type was significant, F(2, 54) = 73.82, p < .001, -rip = .73. Specifically, RTs were faster in the valid condition than in the neutral condition (p < .01), and slower in the invalid than in the neutral condition (p < .01). More importantly, there was a significant interaction between tag type and trial type, F(2, 54) = 18.48, p < .001, rip = .41. This interaction suggests that although the effect of trial type was significant in both the target-tag block, F(2, 108) = 78.65, p < .001, rip = .59, and the distractor-tag block, F(2, 108) = 5.91, p < .01, = .10, the effect was larger for the target-tag block. Follow-up analyses indicated that in the target-tag block, the responses in the invalid condition were slower than those in the neutral condition (p < .01), whereas the re sponses were faster in the valid than the neutral condition (p < .01). In the distractor-tag block, although the responses were slower in the invalid condition in comparison with the neutral condition {p < .05), there was no difference between the valid and neutral conditions (p > .10). Again, the overall main effect of tag type was not significant, F (l, 27) = 0.93, p > .10, t^ = .03. Experiment 3 replicated the findings of Experiments 1 and 2 with an orientation discrimination task. The results showed that the tag associated with an item held in working memory affected working memory-driven attentional capture. This effect of attentional capture was greater when the item was associated with a target tag and less when the item was associated with a distractor tag. In addition, the response benefit in the valid condition compared with the neutral condition, which was a nonsignificant trend in Experiment 2, was reliable in the target-tag condition of the present experiment. This indicates that when the memorized item is associated with a target tag, stimuli matching the memorized item better capture attention.
Method Participants. Twenty-eight undergraduate participants from the National Taiwan University participated in the current study for either course credit or NTS 100. All participants had normal or corrected-to-normal vision. Procedure. All aspects of the study were similar to those in Experiment 2, with a few exceptions. Namely, an orientation discrimination task replaced the motion discrimination task used in Experiments 1 and 2. In the current task, a line was presented through each of the colored circles. The participants were told to look for a tilted target line and to judge the orientation of the tilt. In addition, two squares with a notch in either the top or bottom were surrounded by colored circles, presented as the recognition display. Participants were required to indicate whether the square in the colored circle that matched (target-tag block) or mismatched (distractor-tag block) the memorized color had a notch on its top or bottom. Figure IB shows the sequence of events for a typical trial. The total number of experimental trials was 144, with each con dition consisting of 24 trials.
Tag T y p e
Figure 4. Mean correct response times (RTs) in the selection task as a function of trial type and tag type in Experiment 3. Error bars represent SEs. The black bars show the performance in the invalid condition, the dark gray bars show performance in the neutral condition, and the light gray bars show the performance in the valid condition.
ROLE OF ATTENTIONAL TAGS
Experiment 4 Experiments 1-3 clearly demonstrated the impact of attentional tags on working memory-driven attentional capture. Although items associated with a target tag captured attention, items asso ciated with a distractor tag produced a smaller effect in terms of attentional capture, or did not capture attention at all. Attentional tags may modulate attentional capture in at least two ways. First, it is possible that once a memorized item is associated with a distractor tag, attentional capture is reduced regardless of the time course. However, it is also possible that attention is automatically initially captured by stimuli matching items associ ated with the distractor tag, but that this is followed by a deliberate attentional inhibition and disengagement from those stimuli. For instance, assuming that attentional inhibition is a mechanism of cognitive control, Han and Kim (2009) demonstrated that the impact of cognitive control on working memory-driven attentional capture requires time to develop, consistent with the second the ory. To distinguish between these two possibilities, we manipulated the timing in the motion discrimination task of Experiments 1 and 2. In the original task, two colored circles were presented for 187 ms before one of them moved upward or downward. In Experi ment 4, the delay before the motion was either shortened (68 ms) or lengthened (340 ms). If attention is immediately captured by a stimulus that matches the distractor tag, attentional capture would only be expected in the short-delay condition. On the other hand, if attention capture is less likely to occur for distractor-related items, regardless of the time course, reduced or eliminated atten tional capture would be expected in both the short-delay and long-delay conditions.
Method Participants. Thirty volunteers received a NT$100 payment for their participation in Experiment 4. All participants had normal or corrected-to-normal vision. Procedure. All aspects of Experiment 4 were identical to Experiment 2, with the exception of the time manipulation. In Experiment 4, the two colored circles presented in the motion discrimination task appeared for either 68 ms (short delay) or 340 ms (long delay) before moving. Because of the addition of this new variable, the number of conditions in Experiment 4 was doubled, resulting in 12 conditions of 24 trials each, for a total of 288 trials.
Results and Discussion The accuracy was at ceiling in both the motion discrimination (99%) and recognition task (97%). Figure 5 shows RT data for the motion discrimination task. A 2 (tag type: target tag or distractor tag) X 2 (delay of motion: 68/340 ms) X 3 (trial type: invalid, neutral, or valid) repeated measures ANOVA on motion discrim ination RT revealed that the main effect of trial type was signifi cant, F(2, 58) = 8.97, p < .001, -r^ = .24. RTs were slower in the invalid condition than in the neutral condition (p < .05) and valid condition (p < .01). In addition, the main effect of delay of motion was also significant, F (l, 29) = 35.97, p < .001, rip = .55. More important, there was a significant two-way interaction between tag type and trial type, F(2, 58) = 18.59, p < .001, rip = .39. First,
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Figure 5. Mean correct response times (RTs) in the selection task as a function of trial type and delay time (short = 68 ms, long = 340 ms) in the target-tag and distractor-tag blocks in Experiment 4. Error bars represent SEs. The black bars depict performance in the invalid condition, the dark gray bars show the performance in the neutral condition, and the light gray bars show performance in the valid condition.
although significant in both blocks, the effect of trial type was larger in the target-tag block, F(2, 116) = 27.49, p < .001, -rip = .32, than in the distractor-tag block, F(2, 116) = 4.28, p = .02, T)p = .07. Second, the effect of trial type was different for the target-tag and distractor-tag conditions. In the target-tag con dition, RTs were faster in the valid condition than in the neutral and invalid conditions (ps < .01), and RTs in the invalid condition were slower than in the neutral condition (p < .01). Conversely, in the distractor-tag condition, RTs were slower in the valid than in the invalid condition (p < .05). In other words, a reversed pattern was observed for trial type in the distractortag and target-tag conditions. Other main effects and interac tions were not significant, ps > .10. Experiment 4 replicated the findings of Experiments 1 and 2. Although attention was captured by the stimuli matching the item associated with a target tag, this effect did not occur when the items held in working memory were associated with a distractor tag. In fact, responses to the stimuli matching the items associated with a distractor tag were delayed, suggesting a possible atten tional inhibition effect. In Experiment 4, the timing of the motion discrimination task was changed to either 68 ms or 340 ms before movement, com pared with 187 ms in Experiments 1 and 2. The influence of attentional tags on working memory-driven attentional capture was observed in all experiments, but there was no effect of timing in Experiment 4. These results suggest that, at least for the durations used in the current study, the impact of attentional tags on working memory-driven attentional capture remained similar irrespective of the timings used. The idea that attention is initially captured by a stimulus matching the item stored in working memory, regard less of the attentional tags, was not supported.
General Discussion According to the biased competition model (Desimone & Dun can, 1995), a target template stored in working memory biases
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attention toward a stimulus that matches that template. Consistent with this model, it has been demonstrated that the contents of working memory can capture attention (e.g., Downing, 2000; Han & Kim, 2009; Houtkamp & Roelfsema, 2006; Kuo et al., 2013; Olivers et al., 2006; Soto et al., 2005; Woodman & Luck, 2007). In daily life, people remember not only the objects they wish to pay attention to but also items they do not mean to attend to. In other words, distractors as well as targets are maintained in work ing memory. This raises an intriguing and important issue: because items held in working memory may be associated with different task demands and attentional tags, do items associated with a target tag (i.e., this item is the target in a follow-up task) and items associated with a distractor tag (i.e., this item is the distractor in a follow-up task) capture attention in the same manner? In the present study, a memory task was combined with a motion discrimination task (Experiments 1, 2, and 4) or an orien tation discrimination task (Experiment 3) to examine working memory-driven attentional capture. The item held in working memory was either the target or the distractor for the memory task. Hence, the working memory items were associated with a target tag or a distractor tag. The results showed that not all items stored in working memory capture attention. When a stimulus matched a memorized item associated with a target tag, it captured attention. In contrast, when a stimulus matched a memorized item associated with a distractor tag, it was less effective at capturing attention. Thus, these findings demonstrate that the interaction between working memory and attention is flexible and modulated by the attentional tags associated with the memorized items. The attention system may process the distractor tags in two ways. First, it is possible that all items in working memory initially automatically capture attention, but a secondary control mecha nism that is sensitive to attentional tags later suppresses this attentional capture when the items are associated with a distractor tag. Second, it is possible that when using the contents of working memory to guide attention, the items and the attentional tags in working memory are processed together. Thus, when items are associated with a distractor tag, attentional capture by stimuli matching this tag is suppressed. In Experiment 4 of the present study, the variation of delay time before object motion did not affect working memory-driven attentional capture. Therefore, the findings are consistent with the idea that the memorized item and its associated attentional tags are processed together, dictating the potential for attentional capture. When items are associated with distractor tags, the attentional system may either not attend to, or even inhibit (be biased against), stimuli matching these items. The idea of not attending to is consistent with the model in which multiple items can be stored in working memory, but only the item currently being focused on captures attention (Downing & Dodds, 2004). It is possible that when an item is associated with a distractor tag, that item is less likely to be moved into the focus of attention. Hence, a stimulus matching the distractor-tagged item in working memory does not capture attention. Alternatively, the idea of inhibition is consistent with the recent findings that knowledge about an upcoming dis tractor can facilitate responses to a target either by deliberately avoiding that distractor (Arita et al., 2012), or by actively inhib iting attention to it (Chao, 2010, 2011). In the present study, the results were conflicting in this regard. In Experiment 4, slower responses to valid trials in the distractor-tag condition suggests that
items associated with distractor tags may result in an inhibition of responses to matched items. However, in Experiments 2 and 3, this pattern was either nonsignificant (Experiment 2) or not observed (Experiment 3). Hence, it appears that the theory of inhibition is possible but requires further investigation. The flexible use of working memory in guiding attention can be achieved by altering memory representations in at least two ways. Olivers (2009) found that the memorized item did not capture attention in the visual search task when the visual search target was altered trial-by-trial, therefore, requiring the participants to main tain two items in their working memory. Because multiple items were stored in working memory, the participants had to assign different priorities to these items, or make a clear distinction between the item for the visual search task and that for the final memory task. In this scenario, because the to-be-memorized item was given a lower priority during the visual search task, it had less of an effect on visual search performance. In other words, working memory-driven attentional capture can be adjusted according to the priority assigned to the memorized item. In a second experi ment, Olivers and Eimer (2011) manipulated the order of the visual search task and the memory test, as well as altering whether the trials were blocked or mixed. The most critical finding was that when there was the potential for the to-be-memorized item to be the target in the first task (i.e., when the orders of these two tasks were mixed) and the visual search task was the first task, the to-be-memorized item had greater effect on visual search perfor mance. Such findings indicate that working memory-driven atten tional capture is greater when the to-be-memorized item is given a higher priority. It should be noted that the role of attentional tags is different from the role of priority or weighting in working memory-driven attentional capture. In the present study, both the targets and the distractors in the memory task were used as targets for the motion and orientation discrimination tasks with equal frequency. Hence, their priority in these tasks should be the same. As a result, the attentional tags, rather than the task priorities, should modulate the working memory-driven attentional capture in the motion and orientation discrimination tasks. Taken together, this demonstrates that items are stored in working memory in a flexible manner: their priority or weighting can be adjusted, and they can be associated with a variety of attentional tags. Both properties are important in modulating attentional capture. In addition to flexibility in the content of working memory (i.e., adjustable priorities and attentional tags), there may be a control mechanism that allows working memory-driven attentional cap ture to also operate in a flexible manner. Woodman and Luck (2007) found that when memorized items for a later memory test were the never target for a visual search task, the contents of working memory did not affect visual search performance. Fur ther, Carlisle and Woodman (2011) found that increasing the probability that a memorized item would be the target in a visual search task resulted in a larger effect of working memory-driven attentional capture. Finally, Kiyonaga, Egner, and Soto (2012) found that the probability that the memorized item was the target or distractor in the visual search task not only affected working memory-driven attentional capture, but also affected working memory performance. In other words, the memory representations of items stored in working memory were altered. These findings imply that a control mechanism, which is sensitive to the contin-
ROLE OF ATTENTIONAL TAGS
gency between the memorized item and the to-be-searched-for item (and is perhaps sensitive to the priorities and attentional tags discussed above), can modulate how the contents of working memory are used in a visual search task, as well as how the representations are held in working memory. Taken together, items are not simply maintained in working memory, and items in working memory do not capture attention in a uniform manner. Instead, items stored in working memory can be assigned different priorities (Olivers, 2009) and associated with different attentional tags (such as target or distractor tags). This implies that there is a control mechanism that can modulate how the contents of working memory capture our attention.
References Arita, J. T., Carlisle, N„ & Woodman, G. F. (2012). Templates for rejection: Configuring attention to ignore task-irrelevant features. Jour nal o f Experimental Psychology: Human Perception and Performance, 38, 580-584. doi:10.1037/a0027885 Carlisle, N. B., & Woodman, G. F. (2011). Automatic and strategic effects in the guidance of attention by working memory representations. Acta Psychologica, 137, 217-225. doi: 10.1016/j.actpsy.2010.06.012 Chao, H.-F. (2010). Top-down attentional control for distractor locations: The benefit of precuing distractor locations on target localization and discrimination. Journal o f Experimental Psychology: Human Perception and Performance, 36, 303-316. doi:10.1037/a0015790 Chao, H.-F. (2011). Active inhibition of a distractor word: The distractor precue benefit in the Stroop color-naming task. Journal o f Experimental Psychology: Human Perception and Performance, 37, 799-812. doi: 10.1037/a0022191 Desimone, R., & Duncan, J. (1995). Neural mechanisms of selective visual attention. Annual Review o f Neuroscience, 18, 193-222. doi: 10.1146/ annurev.ne. 18.030195.001205 Downing, P. E. (2000). Interactions between visual working memory and selective attention. Psychological Science, 11, 461-473. doi:10.1111/ 1467-9280.00290 Downing, P. E., & Dodds, C. M. (2004). Competition in visual working memory for control of search. Visual Cognition, 11, 689-703. doi: 10.1080/13506280344000446 Han, S. W., & Kim, M. S. (2009). Do the contents of working memory capture attention? Yes, but cognitive control matters. Journal o f Exper imental Psychology: Human Perception and Performance, 35, 12921302. doi: 10.1037/a0016452
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Houtkamp, R., & Roelfsema, P. R. (2006). The effect of items in working memory on the deployment of attention and the eyes during visual search. Journal of Experimental Psychology: Human Perception and Performance, 32, 423-442. doi: 10.1037/0096-1523.32.2.423 Kiyonaga, A., Egner, T., & Soto, D. (2012). Cognitive control over working memory biases of selection. Psychonomic Bulletin & Review, 19, 639-646. doi:10.3758/sl3423-012-0253-7 Kuo, C.-Y., Chao, H.-F., & Yeh, Y.-Y. (2013). Strategic control modulates working memory-driven attentional capture. Experimental Psychology, 60, 3-11. doi: 10.1027/1618-3169/a000167 Lee, Y.-C., & Chao, H.-F. (2012). The role of active inhibitory control in psychological well-being and mindfulness. Personality and Individual Differences, 53, 618-621. doi:10.1016/j.paid.2012.05.001 Olivers, C. N. L. (2009). What drives memory-driven attentional capture? The effects of memory type, display type, and search type. Journal of Experimental Psychology: Human Perception and Performance, 35, 1275-1291. doi: 10.1037/a0013896 Olivers, C. N. L., & Eimer, M. (2011). On the difference between working memory and attentional set. Neuropsychologia, 49, 1553-1558. doi: 10.1016/j .neuropsychologia.2010.11.033 Olivers, C. N. L., Meijer, F., & Theeuwes, J. (2006). Feature-based working memory driven attentional capture: Visual working memory content affects visual attention. Journal o f Experimental Psychology: Human Perception and Performance, 32, 1243-1265. doi: 10.1037/ 0096-1523.32.5.1243 Soto, D., Heinke, D., Humphreys, G. W„ & Blanco, M. J. (2005). Early, involuntary top-down guidance of attention from working memory. Journal of Experimental Psychology: Human Perception and Perfor mance, 31, 248-261. doi: 10.1037/0096-1523.31.2.248 Soto, D., Hodsoll, J., Rotshtein, P„ & Humphreys, G. W. (2008). Auto matic guidance of attention from working memory. Trends in Cognitive Sciences, 12, 342-348. doi:10.1016/j.tics.2008.05.007 Soto, D., & Humphreys, G. W. (2007). Automatic guidance of visual attention from verbal working memory. Journal o f Experimental Psy chology: Human Perception and Performance, 33, 730-737. doi: 10.1037/0096-1523.33.3.730 Woodman, G. F„ & Luck, S. J. (2007). Do the contents of visual working memory automatically influence attentional selection during visual search? Journal o f Experimental Psychology: Human Perception and Performance, 33, 363-377. doi:10.1037/0096-1523.33.2.363
Received March 27, 2013 Revision received February 14, 2014 Accepted February 18, 2014 ■
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© 2014 American Psychological Association 0096-1523/14/S12.00 http://dx.doi.org/10.1037/a0036451
OBSERVATION
Role of Attentional Tags in Working Memory-Driven Attentional Capture Chun-Yu Kuo
Hsuan-Fu Chao
National Taiwan University
Chung Yuan Christian University
Recent studies have demonstrated that the contents of working memory capture attention when perform ing a visual search task. However, it remains an intriguing and unresolved question whether all kinds of items stored in working memory capture attention. The present study investigated this issue by manip ulating the attentional tags (target or distractor) associated with information maintained in working memory. The results showed that working memory-driven attentional capture is a flexible process, and that attentional tags associated with items stored in working memory do modulate attentional capture. When items were tagged as a target, they automatically captured attention; however, when items were tagged as a distractor, attentional capture was reduced. Keywords: working memory, attentional tag, attentional capture
Over the last decade, numerous studies have been published showing that the contents of working memory can capture atten tion (e.g., Downing, 2000; Han & Kim, 2009; Houtkamp & Roelfsema, 2006; Kuo, Chao, & Yeh, 2013; Olivers, Meijer, & Theeuwes, 2006; Soto, Heinke, Humphreys, & Blanco, 2005; Soto, Hodsoll, Rotshtein, & Humphreys, 2008; Woodman & Luck, 2007). This is usually demonstrated by combining a working memory task with a visual search task. At the beginning of a trial, participants are instructed to remember an item for a memory test they will be given at the end of the trial. Between the study phase and the memory test, participants perform a separate visual search task. The critical finding is that although the memorized item is unrelated to the visual search task, it still captures the participants’ attention. For instance, when the memorized item and another item were presented simultaneously as uninformative cues before the onset of the visual search display, participants responded faster when the target was presented in the same location as where the memorized item had been (Downing, 2000). In addition, visual search was faster when the target was presented in a shape that matched the item held in working memory, whereas responses were slower when the distractor was presented in the shape of the memorized item (Soto et al., 2005). Olivers et al. (2006) also demonstrated that a singleton distractor produces more interfer ence when its color matches that of the memorized item.
The literature clearly supports the idea of working memorydriven attentional capture. However, it remains less clear whether all kinds of items held in working memory capture attention in the same manner. More specifically, in complex environments in daily life, we not only remember the people, objects, and events we wish to pay attention to, but also the stimuli to which we do not wish to attend to. The ability to distinguish between what we do and do not want to pay attention to is vital for efficient performance and overall well-being (Lee & Chao, 2012). To achieve this, items we wish to attend to may be tagged with a “target tag” in working memory, whereas those we choose to ignore are given a “distractor tag.” Stimuli matching the target items held in working memory should be attended to, whereas we should inhibit responses to stimuli matching the distractor items, disengaging our attention from them. Although there is ample evidence that the contents of working memory can capture our attention, the effect of target and distractor tags in working memory is yet to be determined. In previous studies investigating working memory-driven atten tional capture, participants were required to memorize items for a later recognition task. In this situation, the memorized items must be tagged as targets for the up-coming recognition task. In con trast, the role of distractor tags in working memory is not clear. Demonstrations of active inhibition (Chao, 2010, 2011) may pro vide indirect evidence for the existence of distractor tags in work ing memory. Chao demonstrated that when participants know the location or identity of the forthcoming distractor, responses to the target are faster than when people do not have information about the distractor in advance. In addition, effects of distractor precuing are reduced or even eliminated under high working memory load. Hence, it is possible that active inhibition of attention to a distrac tor occurs when the stimulus is deliberately allocated a distractor tag in working memory. Arita, Carlisle, and Woodman (2012) also showed that visual search was improved when a distractor was precued, implying that a distractor template in working memory can bias attention away from a stimulus matching that item.
This article was published Online First April 14, 2014. Chun-Yu Kuo, Department of Psychology, National Taiwan University, Taipei, Taiwan; Hsuan-Fu Chao, Department of Psychology, Chung Yuan Christian University, Chung Li, Taiwan. This work was supported by a grant from the National Science Council of Taiwan to Hsuan-Fu Chao, (NSC 99-2410-H-033-024-MY3). Correspondence concerning this article should be addressed to Hsuan-Fu Chao, Department of Psychology, Chung Yuan Christian University, No. 200, Chung Pei Road, Chung Li 32023, Taiwan. E-mail: hfchao@ cycu.edu.tw 1301
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In the current study, we systematically investigated whether items stored in working memory for different task goals influenced working memory-driven attentional capture. To this end, partici pants were required to memorize a color for a memory task at the end of each trial. In one block, the memorized color indicated what would be the target; in the other block, the memorized color signified the distractor. In both cases, the information had to be held in working memory while completing a separate motion discrimination or orientation discrimination task. If the contents of working memory capture attention regardless of the attentional tags assigned to them, working memory-driven attentional capture will be observed in both conditions. Conversely, if these tags play an important role in attention allocation, attentional capture will only be observed when the item held in working memory is associated with the target tag.
all items stored in working memory capturing attention regardless of the nature of the tag. Second, it is possible that the visual system works to inhibit attentional capture to stimuli matching items associated with a distractor tag.
Method Participants. Thirty-four undergraduate students from the National Taiwan University participated in this experiment for either course credit or NTS 100. All participants had normal or corrected-to-normal vision. Procedure. We modified Downing’s (2000) paradigm to ex amine how the information maintained in working memory for a different task influences motion discrimination in various contexts. Figure 1A shows the sequence of events in a trial. Each trial began with a fixation point presented for 500 ms. A colored circle was then presented at the center of the screen for 1,000 ms, and participants were instructed to memorize the color for a memory task at the end of each trial. A fixation point was then presented for 1,500 ms. Next, two colored circles were presented for the motion discrimination task, one on either side of the fixation point, for 187 ms. Then, one of the colored circles moved either upward or downward by 0.5 degrees. After 53 ms, the two colored circles disappeared and a question mark appeared, indicating that partic ipants should enter the motion direction (up or down) of the moving circle. After responding, two new colored circles (one of which matched the memorized color) were presented for the mem ory task, each with a notch on either the top or the bottom. Participants were required to search for the circle that matched (target-tag block) or mismatched (distractor-tag block) the mem orized color, and indicate whether the circle had a notch in its top or bottom.
Experiment 1 Experiment 1 was conducted to examine whether different tags in working memory have different effects on attention allocation. We modified Downing’s (2000) paradigm by combining a motion discrimination task and a memory task. The critical manipulation was whether the item stored in working memory was the target or distractor for the memory task. It should be noted that the items held in working memory and the target or distractor tags associated with each item were unre lated to the demands of the motion discrimination task. However, if these items still modulated performance in the motion discrim ination task, then the effect would be seen as involuntary. In addition, we were particularly interested in the mechanism involved in processing distractor tags. There are at least two possibilities in this regard. First, it is possible that the distractor tag has no effect on working memory-driven attentional capture, with
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Figure 1. The trial sequences in Experiments 1 to 4. Figure 1A is an example of an invalid trial in which the memorized prime was the distractor in the motion discrimination task in Experiments 1 and 2. Figure IB is an example of an invalid trial in which the memorized prime was the target in the orientation discrimination task in Experiment 3. Figure 1C is an example of an invalid trial in which the memorized prime was the distractor in the motion discrimination task in Experiment 4.
ROLE OF ATTENTIONAL TAGS
In half of all trials, the memorized item matched the distractor in the motion discrimination task (invalid condition); in the other half of the trials, the memorized color was not presented in the motion discrimination task (neutral condition). The trials were blocked by tag type, with each block containing 64 trials of either target- or distractor-tag conditions. There were two blocks each of target- and distractor-tag block, resulting in a total of four blocks. The target- and distractor-tag blocks were alternated and counter balanced, such that half of the participants started with target- and the other half started with distractor-tag block. The total number of experimental trials was 128, each experimental condition consist ing of 32 trials.
Results and Discussion Accuracy was at ceiling in both the motion discrimination task (99%) and the memory task (98%). Reaction time (RT) data from the motion discrimination task for trials where both motion dis crimination and memory recognition were correct were analyzed. Trials with RTs longer than 1,800 ms or shorter than 70 ms were excluded. Figure 2 shows the RTs in the motion discrimination task. A 2 (tag type: target tag or distractor tag) X 2 (trial type: invalid or neutral) repeated measures analysis of variance (ANOVA) on motion discrimination RTs showed that the main effect of trial type was significant, F (l, 33) = 9.08, p = .005, tip = .22. In addition, there was a significant interaction between tag type and trial type on RT, F (l, 33) = 9.38, p = .004, ^ = .22. Further analysis showed that performance was faster in the neutral condi tion than in the invalid condition in the target-tag block, F (l, 66) = 18.31, p < .001, r\2p = .22; but there was no difference between neutral and invalid condition in the distractor-tag block, F (l, 66) = 0.10, p = .75, ^p = .002. The main effect of tag type was not significant, F (l, 33) = 0.21, p > .10, rip = .006. Experiment 1 demonstrated the impact of attentional tags on working memory-driven attentional capture. Stimuli matching memorized items associated with target tags were more likely to
Tag T yp e
Figure 2. Mean correct response times (RTs) in the selection task as a function of trial type and tag type in Experiment 1. Error bars represent SEs. The black bars show the performance in the invalid condition, and the dark gray bars depict the performance in the neutral condition.
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capture attention than stimuli given distractor tags. This suggests that attentional capture by items tagged as distractors may be inhibited.
Experiment 2 Experiment 1 showed that there was no working memory-driven attentional capture when the items stored in working memory were associated with a distractor tag. However, because the memorized item was never the target in the motion discrimination task, and given that previous studies have had difficulty observing the effect of attentional capture in this type of situation (Woodman & Luck, 2007), it remained a question whether the findings of Experiment 1 was a special case. Hence, Experiment 2 was aimed at replicating the findings of Experiment 1 with the inclusion of valid trials, in which the target in the motion discrimination task matched the item held in working memory. We hypothesized that the contents of working memory would capture attention when they were associated with a target tag, and that in the valid condition, the responses would be faster than those in the neutral condition. Conversely, the benefit in the valid condition should be reduced when the item stored in working memory was associated with a distractor tag.
Method Participants. Twenty-six undergraduate participants from the National Taiwan University participated in Experiment 2 for either course credit or NT$100. All participants had normal or correctedto-normal vision. Procedure. All aspects of Experiment 2 were identical to Experiment 1, with two exceptions. In Experiment 2, three kinds of Uials (invalid, neutral, and valid) were presented with equal fre quency in random order. There were also now 24 trials in each condition, for a total of 144 experimental trials.
Results and Discussion Accuracy was at ceiling in both the motion discrimination task (98%) and the memory task (96%). Figure 3 shows the RTs in the motion discrimination task. A repeated measures ANOVA for RTs on the motion discrimination task revealed that the main effect of trial type was again significant, F(2, 50) = 7.02, p = .002, = .22. Performance was slower in the invalid condition than that of both the neutral (p < .01) and valid condition {p < .05). In addition, there was a significant interaction between tag type and trial type, F(2, 50) = 5.34, p = .008, i)2 = .18. This interaction arose because the effect of trial type was significant in the targettag block, F(2, 100) = 10.32, p < .001, tip = .17, but not in the distractor-tag block, F(2, 100) = 1.95, p = .19, rip = .04. The performance in the target-tag block was slower in the invalid condition than in the neutral and valid conditions {p < .01). The difference between the valid and neutral conditions was not sig nificant {p > .10). The main effect of tag type was not significant, F (l, 25) = 2.91, p > .10, T|p = .10. Experiment 2 replicated the major findings of Experiment 1: the contents of working memory captured attention when they were associated with a target tag, but not when they were associated with a distractor tag. It should be noted that although there was a
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Results and Discussion
Tag T y p e
Figure 3. Mean correct response times (RTs) in the selection task as a function of trial type and tag type in Experiment 2. Error bars represent SEs. The black bars show the performance in the invalid condition, the dark gray bars show the performance in the neutral condition, and the light gray bars depict performance in the valid condition.
trend of a response benefit (17 ms) in the valid condition when the items stored in working memory were associated with a target tag, this did not reach significance. Thus, the following experiments were conducted using the valid condition to examine whether there is a specific response benefit to stimuli matching the contents of working memory with the target tag.
Experiment 3 Experiment 3 aimed to test the generality of the results from Experiments 1 and 2. Although the motion discrimination task used in Experiments 1 and 2 has been used in several studies on working memory-driven attention capture (e.g., Downing, 2000; Kuo et al., 2013), the orientation discrimination task has also successfully been used to measure this effect (e.g., Soto et ah, 2005; Soto & Humphreys, 2007). Hence, we used the orientation discrimination task in Experiment 3 to replicate Experiments 1 and 2.
Accuracy was at ceiling in both the orientation discrimination task (99%) and the recognition task (98%). Figure 4 shows the RTs for the orientation discrimination task. A repeated measures ANOVA for orientation discrimination RTs revealed that the main effect of trial type was significant, F(2, 54) = 73.82, p < .001, -rip = .73. Specifically, RTs were faster in the valid condition than in the neutral condition (p < .01), and slower in the invalid than in the neutral condition (p < .01). More importantly, there was a significant interaction between tag type and trial type, F(2, 54) = 18.48, p < .001, rip = .41. This interaction suggests that although the effect of trial type was significant in both the target-tag block, F(2, 108) = 78.65, p < .001, rip = .59, and the distractor-tag block, F(2, 108) = 5.91, p < .01, = .10, the effect was larger for the target-tag block. Follow-up analyses indicated that in the target-tag block, the responses in the invalid condition were slower than those in the neutral condition (p < .01), whereas the re sponses were faster in the valid than the neutral condition (p < .01). In the distractor-tag block, although the responses were slower in the invalid condition in comparison with the neutral condition {p < .05), there was no difference between the valid and neutral conditions (p > .10). Again, the overall main effect of tag type was not significant, F (l, 27) = 0.93, p > .10, t^ = .03. Experiment 3 replicated the findings of Experiments 1 and 2 with an orientation discrimination task. The results showed that the tag associated with an item held in working memory affected working memory-driven attentional capture. This effect of attentional capture was greater when the item was associated with a target tag and less when the item was associated with a distractor tag. In addition, the response benefit in the valid condition compared with the neutral condition, which was a nonsignificant trend in Experiment 2, was reliable in the target-tag condition of the present experiment. This indicates that when the memorized item is associated with a target tag, stimuli matching the memorized item better capture attention.
Method Participants. Twenty-eight undergraduate participants from the National Taiwan University participated in the current study for either course credit or NTS 100. All participants had normal or corrected-to-normal vision. Procedure. All aspects of the study were similar to those in Experiment 2, with a few exceptions. Namely, an orientation discrimination task replaced the motion discrimination task used in Experiments 1 and 2. In the current task, a line was presented through each of the colored circles. The participants were told to look for a tilted target line and to judge the orientation of the tilt. In addition, two squares with a notch in either the top or bottom were surrounded by colored circles, presented as the recognition display. Participants were required to indicate whether the square in the colored circle that matched (target-tag block) or mismatched (distractor-tag block) the memorized color had a notch on its top or bottom. Figure IB shows the sequence of events for a typical trial. The total number of experimental trials was 144, with each con dition consisting of 24 trials.
Tag T y p e
Figure 4. Mean correct response times (RTs) in the selection task as a function of trial type and tag type in Experiment 3. Error bars represent SEs. The black bars show the performance in the invalid condition, the dark gray bars show performance in the neutral condition, and the light gray bars show the performance in the valid condition.
ROLE OF ATTENTIONAL TAGS
Experiment 4 Experiments 1-3 clearly demonstrated the impact of attentional tags on working memory-driven attentional capture. Although items associated with a target tag captured attention, items asso ciated with a distractor tag produced a smaller effect in terms of attentional capture, or did not capture attention at all. Attentional tags may modulate attentional capture in at least two ways. First, it is possible that once a memorized item is associated with a distractor tag, attentional capture is reduced regardless of the time course. However, it is also possible that attention is automatically initially captured by stimuli matching items associ ated with the distractor tag, but that this is followed by a deliberate attentional inhibition and disengagement from those stimuli. For instance, assuming that attentional inhibition is a mechanism of cognitive control, Han and Kim (2009) demonstrated that the impact of cognitive control on working memory-driven attentional capture requires time to develop, consistent with the second the ory. To distinguish between these two possibilities, we manipulated the timing in the motion discrimination task of Experiments 1 and 2. In the original task, two colored circles were presented for 187 ms before one of them moved upward or downward. In Experi ment 4, the delay before the motion was either shortened (68 ms) or lengthened (340 ms). If attention is immediately captured by a stimulus that matches the distractor tag, attentional capture would only be expected in the short-delay condition. On the other hand, if attention capture is less likely to occur for distractor-related items, regardless of the time course, reduced or eliminated atten tional capture would be expected in both the short-delay and long-delay conditions.
Method Participants. Thirty volunteers received a NT$100 payment for their participation in Experiment 4. All participants had normal or corrected-to-normal vision. Procedure. All aspects of Experiment 4 were identical to Experiment 2, with the exception of the time manipulation. In Experiment 4, the two colored circles presented in the motion discrimination task appeared for either 68 ms (short delay) or 340 ms (long delay) before moving. Because of the addition of this new variable, the number of conditions in Experiment 4 was doubled, resulting in 12 conditions of 24 trials each, for a total of 288 trials.
Results and Discussion The accuracy was at ceiling in both the motion discrimination (99%) and recognition task (97%). Figure 5 shows RT data for the motion discrimination task. A 2 (tag type: target tag or distractor tag) X 2 (delay of motion: 68/340 ms) X 3 (trial type: invalid, neutral, or valid) repeated measures ANOVA on motion discrim ination RT revealed that the main effect of trial type was signifi cant, F(2, 58) = 8.97, p < .001, -r^ = .24. RTs were slower in the invalid condition than in the neutral condition (p < .05) and valid condition (p < .01). In addition, the main effect of delay of motion was also significant, F (l, 29) = 35.97, p < .001, rip = .55. More important, there was a significant two-way interaction between tag type and trial type, F(2, 58) = 18.59, p < .001, rip = .39. First,
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Figure 5. Mean correct response times (RTs) in the selection task as a function of trial type and delay time (short = 68 ms, long = 340 ms) in the target-tag and distractor-tag blocks in Experiment 4. Error bars represent SEs. The black bars depict performance in the invalid condition, the dark gray bars show the performance in the neutral condition, and the light gray bars show performance in the valid condition.
although significant in both blocks, the effect of trial type was larger in the target-tag block, F(2, 116) = 27.49, p < .001, -rip = .32, than in the distractor-tag block, F(2, 116) = 4.28, p = .02, T)p = .07. Second, the effect of trial type was different for the target-tag and distractor-tag conditions. In the target-tag con dition, RTs were faster in the valid condition than in the neutral and invalid conditions (ps < .01), and RTs in the invalid condition were slower than in the neutral condition (p < .01). Conversely, in the distractor-tag condition, RTs were slower in the valid than in the invalid condition (p < .05). In other words, a reversed pattern was observed for trial type in the distractortag and target-tag conditions. Other main effects and interac tions were not significant, ps > .10. Experiment 4 replicated the findings of Experiments 1 and 2. Although attention was captured by the stimuli matching the item associated with a target tag, this effect did not occur when the items held in working memory were associated with a distractor tag. In fact, responses to the stimuli matching the items associated with a distractor tag were delayed, suggesting a possible atten tional inhibition effect. In Experiment 4, the timing of the motion discrimination task was changed to either 68 ms or 340 ms before movement, com pared with 187 ms in Experiments 1 and 2. The influence of attentional tags on working memory-driven attentional capture was observed in all experiments, but there was no effect of timing in Experiment 4. These results suggest that, at least for the durations used in the current study, the impact of attentional tags on working memory-driven attentional capture remained similar irrespective of the timings used. The idea that attention is initially captured by a stimulus matching the item stored in working memory, regard less of the attentional tags, was not supported.
General Discussion According to the biased competition model (Desimone & Dun can, 1995), a target template stored in working memory biases
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attention toward a stimulus that matches that template. Consistent with this model, it has been demonstrated that the contents of working memory can capture attention (e.g., Downing, 2000; Han & Kim, 2009; Houtkamp & Roelfsema, 2006; Kuo et al., 2013; Olivers et al., 2006; Soto et al., 2005; Woodman & Luck, 2007). In daily life, people remember not only the objects they wish to pay attention to but also items they do not mean to attend to. In other words, distractors as well as targets are maintained in work ing memory. This raises an intriguing and important issue: because items held in working memory may be associated with different task demands and attentional tags, do items associated with a target tag (i.e., this item is the target in a follow-up task) and items associated with a distractor tag (i.e., this item is the distractor in a follow-up task) capture attention in the same manner? In the present study, a memory task was combined with a motion discrimination task (Experiments 1, 2, and 4) or an orien tation discrimination task (Experiment 3) to examine working memory-driven attentional capture. The item held in working memory was either the target or the distractor for the memory task. Hence, the working memory items were associated with a target tag or a distractor tag. The results showed that not all items stored in working memory capture attention. When a stimulus matched a memorized item associated with a target tag, it captured attention. In contrast, when a stimulus matched a memorized item associated with a distractor tag, it was less effective at capturing attention. Thus, these findings demonstrate that the interaction between working memory and attention is flexible and modulated by the attentional tags associated with the memorized items. The attention system may process the distractor tags in two ways. First, it is possible that all items in working memory initially automatically capture attention, but a secondary control mecha nism that is sensitive to attentional tags later suppresses this attentional capture when the items are associated with a distractor tag. Second, it is possible that when using the contents of working memory to guide attention, the items and the attentional tags in working memory are processed together. Thus, when items are associated with a distractor tag, attentional capture by stimuli matching this tag is suppressed. In Experiment 4 of the present study, the variation of delay time before object motion did not affect working memory-driven attentional capture. Therefore, the findings are consistent with the idea that the memorized item and its associated attentional tags are processed together, dictating the potential for attentional capture. When items are associated with distractor tags, the attentional system may either not attend to, or even inhibit (be biased against), stimuli matching these items. The idea of not attending to is consistent with the model in which multiple items can be stored in working memory, but only the item currently being focused on captures attention (Downing & Dodds, 2004). It is possible that when an item is associated with a distractor tag, that item is less likely to be moved into the focus of attention. Hence, a stimulus matching the distractor-tagged item in working memory does not capture attention. Alternatively, the idea of inhibition is consistent with the recent findings that knowledge about an upcoming dis tractor can facilitate responses to a target either by deliberately avoiding that distractor (Arita et al., 2012), or by actively inhib iting attention to it (Chao, 2010, 2011). In the present study, the results were conflicting in this regard. In Experiment 4, slower responses to valid trials in the distractor-tag condition suggests that
items associated with distractor tags may result in an inhibition of responses to matched items. However, in Experiments 2 and 3, this pattern was either nonsignificant (Experiment 2) or not observed (Experiment 3). Hence, it appears that the theory of inhibition is possible but requires further investigation. The flexible use of working memory in guiding attention can be achieved by altering memory representations in at least two ways. Olivers (2009) found that the memorized item did not capture attention in the visual search task when the visual search target was altered trial-by-trial, therefore, requiring the participants to main tain two items in their working memory. Because multiple items were stored in working memory, the participants had to assign different priorities to these items, or make a clear distinction between the item for the visual search task and that for the final memory task. In this scenario, because the to-be-memorized item was given a lower priority during the visual search task, it had less of an effect on visual search performance. In other words, working memory-driven attentional capture can be adjusted according to the priority assigned to the memorized item. In a second experi ment, Olivers and Eimer (2011) manipulated the order of the visual search task and the memory test, as well as altering whether the trials were blocked or mixed. The most critical finding was that when there was the potential for the to-be-memorized item to be the target in the first task (i.e., when the orders of these two tasks were mixed) and the visual search task was the first task, the to-be-memorized item had greater effect on visual search perfor mance. Such findings indicate that working memory-driven atten tional capture is greater when the to-be-memorized item is given a higher priority. It should be noted that the role of attentional tags is different from the role of priority or weighting in working memory-driven attentional capture. In the present study, both the targets and the distractors in the memory task were used as targets for the motion and orientation discrimination tasks with equal frequency. Hence, their priority in these tasks should be the same. As a result, the attentional tags, rather than the task priorities, should modulate the working memory-driven attentional capture in the motion and orientation discrimination tasks. Taken together, this demonstrates that items are stored in working memory in a flexible manner: their priority or weighting can be adjusted, and they can be associated with a variety of attentional tags. Both properties are important in modulating attentional capture. In addition to flexibility in the content of working memory (i.e., adjustable priorities and attentional tags), there may be a control mechanism that allows working memory-driven attentional cap ture to also operate in a flexible manner. Woodman and Luck (2007) found that when memorized items for a later memory test were the never target for a visual search task, the contents of working memory did not affect visual search performance. Fur ther, Carlisle and Woodman (2011) found that increasing the probability that a memorized item would be the target in a visual search task resulted in a larger effect of working memory-driven attentional capture. Finally, Kiyonaga, Egner, and Soto (2012) found that the probability that the memorized item was the target or distractor in the visual search task not only affected working memory-driven attentional capture, but also affected working memory performance. In other words, the memory representations of items stored in working memory were altered. These findings imply that a control mechanism, which is sensitive to the contin-
ROLE OF ATTENTIONAL TAGS
gency between the memorized item and the to-be-searched-for item (and is perhaps sensitive to the priorities and attentional tags discussed above), can modulate how the contents of working memory are used in a visual search task, as well as how the representations are held in working memory. Taken together, items are not simply maintained in working memory, and items in working memory do not capture attention in a uniform manner. Instead, items stored in working memory can be assigned different priorities (Olivers, 2009) and associated with different attentional tags (such as target or distractor tags). This implies that there is a control mechanism that can modulate how the contents of working memory capture our attention.
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Houtkamp, R., & Roelfsema, P. R. (2006). The effect of items in working memory on the deployment of attention and the eyes during visual search. Journal of Experimental Psychology: Human Perception and Performance, 32, 423-442. doi: 10.1037/0096-1523.32.2.423 Kiyonaga, A., Egner, T., & Soto, D. (2012). Cognitive control over working memory biases of selection. Psychonomic Bulletin & Review, 19, 639-646. doi:10.3758/sl3423-012-0253-7 Kuo, C.-Y., Chao, H.-F., & Yeh, Y.-Y. (2013). Strategic control modulates working memory-driven attentional capture. Experimental Psychology, 60, 3-11. doi: 10.1027/1618-3169/a000167 Lee, Y.-C., & Chao, H.-F. (2012). The role of active inhibitory control in psychological well-being and mindfulness. Personality and Individual Differences, 53, 618-621. doi:10.1016/j.paid.2012.05.001 Olivers, C. N. L. (2009). What drives memory-driven attentional capture? The effects of memory type, display type, and search type. Journal of Experimental Psychology: Human Perception and Performance, 35, 1275-1291. doi: 10.1037/a0013896 Olivers, C. N. L., & Eimer, M. (2011). On the difference between working memory and attentional set. Neuropsychologia, 49, 1553-1558. doi: 10.1016/j .neuropsychologia.2010.11.033 Olivers, C. N. L., Meijer, F., & Theeuwes, J. (2006). Feature-based working memory driven attentional capture: Visual working memory content affects visual attention. Journal o f Experimental Psychology: Human Perception and Performance, 32, 1243-1265. doi: 10.1037/ 0096-1523.32.5.1243 Soto, D., Heinke, D., Humphreys, G. W„ & Blanco, M. J. (2005). Early, involuntary top-down guidance of attention from working memory. Journal of Experimental Psychology: Human Perception and Perfor mance, 31, 248-261. doi: 10.1037/0096-1523.31.2.248 Soto, D., Hodsoll, J., Rotshtein, P„ & Humphreys, G. W. (2008). Auto matic guidance of attention from working memory. Trends in Cognitive Sciences, 12, 342-348. doi:10.1016/j.tics.2008.05.007 Soto, D., & Humphreys, G. W. (2007). Automatic guidance of visual attention from verbal working memory. Journal o f Experimental Psy chology: Human Perception and Performance, 33, 730-737. doi: 10.1037/0096-1523.33.3.730 Woodman, G. F„ & Luck, S. J. (2007). Do the contents of visual working memory automatically influence attentional selection during visual search? Journal o f Experimental Psychology: Human Perception and Performance, 33, 363-377. doi:10.1037/0096-1523.33.2.363
Received March 27, 2013 Revision received February 14, 2014 Accepted February 18, 2014 ■
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