Reset a task set after five minutes of mindfulness practice

Consciousness and Cognition 35 (2015) 98–109

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Consciousness and Cognition journal homepage: www.elsevier.com/locate/concog

Reset a task set after five minutes of mindfulness practice Chun-Yu Kuo a, Yei-Yu Yeh b,⇑ a b

Chung Yuan Christian University, Chung Li, Taiwan Department of Psychology, National Taiwan University, Taipei, Taiwan

a r t i c l e

i n f o

Article history: Received 1 November 2014

Keywords: Mindfulness Task-set inertia Attentional capture Attentional control

a b s t r a c t This study aimed to evaluate the impact of a brief mindfulness practice on reducing the carryover effect caused by a previous task set and to determine the mechanism for its effectiveness. Experiment 1 showed that a memorized color interfered with subsequent visual search as a singleton distractor only when color was a defining feature for the search target. In Experiment 2, three interventions (scene-viewing, distraction, and mindfulness practice) were implemented across three groups for five minutes between two blocks; color was relevant to search in the first block and irrelevant in the second. Only the mindfulness group showed a non-significant carryover effect. Experiment 3 demonstrated that the scene-viewing participants continued adopting a suppressive mode of attentional control on a previously distracting color during letter judgment. In contrast, mindfulness practice could reset a task set. Mindfulness practice could enhance concentration in the present moment via reconfiguring the mode of attentional control. Ó 2015 Elsevier Inc. All rights reserved.

1. Introduction What is on the mind may interfere with the present task even when the activated mental set is irrelevant to the current behavioral goal. Moreover, this processing mode may carry over to the subsequent task when the task shares similar elements. The current study is interested in how this carryover could be reset. Specifically, we investigate whether a brief period of mindfulness practice, attentional restoration, or distraction can disrupt a carryover effect induced by the previous task set. Given the effectiveness of mindfulness practice, we investigated the underlying mechanism for its effectiveness in a context that occurs in everyday life. 1.1. Task-set inertia (TSI) Imagine driving to work: you should focus on the current task-relevant stimuli involving the traffic lights, the pedestrians, and other cars on the road. In addition to all these current task-relevant stimuli, your attention may also be captured by many irrelevant stimuli lingering from previous episodes, such as a gift shop for holiday shopping that you were just discussing with your family. The interference caused by previous mental processes reflects task-set inertia (TSI); TSI results in poor performance when people must switch from one task to another in a similar context (see Monsell, 2003, for a review).

⇑ Corresponding author at: Department of Psychology, National Taiwan University, No. 1 Sec. 4 Roosevelt Rd., Taipei 106, Taiwan. Fax: +886 2362 9909. E-mail address: [email protected] (Y.-Y. Yeh). http://dx.doi.org/10.1016/j.concog.2015.04.023 1053-8100/Ó 2015 Elsevier Inc. All rights reserved.

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Task set is a configuration of the perceptual, attentional, mnemonic, and motor processes required to perform a task (see Sakai, 2008, for a review). The appropriate configuration of the mental set (Jersild, 1927), mental resources, procedural schema or task-set (Monsell, 2003) is necessary to effectively select and process task-relevant information (Pashler, 1998). Once people have established a task set, they may continue using the same set when the subsequent task shares similar elements with the previous task. Empirical research on task switching has demonstrated this phenomenon, showing poor performance when people must switch from one task to another sharing the same set of stimuli (Allport, Styles, & Hsieh, 1994; Wylie & Allport, 2000; Yeung & Monsell, 2003). Switching to another task requires reconfiguration of the task rule, the attentional weighing of various perceptual features, and the stimulus-response mapping rule to delay responses. TSI, reflected by the switching cost, can be transient from one trial to the next (see Monsell, 2003, for a review) or long-term after performing one task through multiple trials or a block of trials (Mayr, 2002; Waszak, Hommel, & Allport, 2003). TSI may proceed without conscious awareness because unconscious representation can modulate TSI (Lau & Passingham, 2007; Reuss, Kiesel, Kunde, & Hommel, 2011; Weibel, Giersch, Dehaene, & Huron, 2013). Importantly, TSI is robust because a long preparation interval can reduce but not eliminate the inertia (see Monsell, 2003, for a review). 1.2. Mindfulness training improves general cognition If a long interval of preparation cannot eliminate TSI, what would be an effective intervention to eliminate TSI? We addressed this issue with a focus on mindfulness practice. Mindfulness practice requires self-regulating the focus of attention on the present moment without judgment while inhibiting the elaboration on irrelevant thoughts (Marlatt & Kristeller, 1999). Marlatt (1994) suggested that mindfulness can address changing situations in an adaptive way to focus on the present moment. Mindfulness-based interventions have been proven clinically effective for reducing pain, stress, anxiety, depressive relapse, and eating disorders (see Baer, 2003, for a review). It has also been demonstrated that mindfulness-based interventions can enhance cognitive abilities, including attention, memory and executive functions in non-clinic populations (see Chiesa, Calati, & Serretti, 2011, for a review). Mindfulness, as a promising strategy for improving task focus and performance, has been shown to reduce mind wandering in a vigilance task (Mrazek, Smallwood, & Schooler, 2012). Malinowski (2013) emphasized the central role of attentional control for the benefits of mindfulness practice on physical well-being, behaviors, or mental well-being. Mindfulness training, which focuses on ‘‘pay attention to the present experience’’, increases alertness (Anderson, Lau, Segal, & Bishop, 2007; Jha, Krompinger, & Baime, 2007), which may improve awareness of physical sensations (Dickenson, Berkman, Arch, & Lieberman, 2013). Mindfulness facilitates orienting and detecting new stimuli (Anderson et al., 2007; Fernandez-Duque & Posner, 1997). Mindfulness training also benefits attentional control functions such as voluntary attentional control, conflict monitoring (Jha et al., 2007), mental set shifting (Dickenson et al., 2013), flexibility in re-directing attention to new information (Hodgins & Adair, 2010) and the inhibition of non-relevant proponent responses (Heeren, Van Broeck, & Philippot, 2009). If mindfulness practice can improve attentional control and cognitive flexibility, this practice should be effective for reducing or eliminating TSI. After mindfulness practice, conscious awareness of the present moment should enable people to disengage from the previous task set and focus on the current task rule. Mindfulness practice should be an effective intervention to eliminate the TSI effect. However, evidence is equivocal in supporting the benefit of mindfulness training on task switching. Expert meditators were better at attentional switching than non-meditators (Hodgins & Adair, 2010), but the benefit of mindfulness training on attentional switching was not observed among new learners compared with the control group (Anderson et al., 2007; Chambers, Lo, & Allen, 2008; Heeren et al., 2009). Moreover, the contrast between experts and non-meditators may reflect an enhancement of general cognitive abilities rather than providing direct evidence supporting that people can reconfigure a task set after mindfulness practice. We aimed to provide direct evidence and uncover the mechanism underlying the effectiveness of mindfulness practice. 1.3. The current study To investigate whether mindfulness practice can reduce or eliminate TSI and to determine the mechanism underlying its effectiveness, we conducted three experiments. In all three experiments, a color set was introduced before the participants performed another task. In Experiment 1, the color set was established by requiring the participants to remember a color for subsequent recognition while performing a visual search task. The memory activation capture (MAC) effect, reflecting the interference caused by the memorized color as a distractor in visual search compared with the neutral condition in which the memorized color did not occur in visual search, was the result of validating the influence of a color set. Experiment 1 verified a hypothesis that the MAC effect would be observed in a demanding search task only when color was relevant to the search goal. Three interventions (mindfulness, scene-viewing, and distraction) were incorporated across three groups in Experiment 2; color was relevant to the search goal in the first block and irrelevant in the second block. The results of interest relate to the carryover effect, the TSI, in the second block. If an intervention is not effective for reducing or eliminating the TSI, we should observe the MAC effect in the second block due to continued operation of the task set established in the first block. If an intervention is effective, we should not observe the MAC in the second block. An intervention lasted for five minutes between the two blocks.

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In Experiment 3, we investigated whether reconfiguration of the mode of attentional control underlies the effectiveness of mindfulness practice. The color set was introduced through a contingency that related a memorized color to the target or a distractor in a singleton visual search. The influence of this color set was measured in a subsequent letter judgment task that required the participants to judge the identity of a colored letter. On the basis of Moher, Lakshmanan, Egeth, and Ewen’s study (2014), we expected poor performance when the letter was printed in the distractor color, as the participants would carry the inhibitory processes to the letter judgment. Two interventions (mindfulness and scene-viewing) were adopted. The carryover effect was the result of interest. If an intervention is effective for reconfiguring the mode of attentional control, we should not observe the interference in judgment when the letter is printed in the distractor color. 2. Experiment 1 The objective of this experiment is to investigate a constraint of the MAC effect. In many MAC studies, participants need to maintain an item in working memory while searching for a target (Downing, 2000; Olivers, Meijer, & Theeuwes, 2006; Soto, Heinke, Humphreys, & Blanco, 2005; Soto, Hodsoll, Rotshtein, & Humphreys, 2008). The memorized item, irrelevant to the search goal, is presented as a distractor in the search array in the invalid condition. The slowing of performance in the invalid condition compared with the neutral condition (the memorized item is not presented) reflects the interference from the memorized item, that is the MAC effect. The MAC effect provides a dynamic ‘‘snapshot’’ of the contents activated in working memory at the present moment (Lange, Thomas, Buttaccio, & Davelaar, 2012). The MAC effect has its boundaries. When the search task is highly demanding, the content maintained in working memory may not capture attention. Woodman and Luck (2007) in their first experiment showed that a color maintained in working memory does not capture attention when the participants must search through a display of six colored squares for a notched target and judge the direction of the notch. A color maintained in working memory does not interfere with visual search as a distractor when color is no longer a part of the task set configured for the demanding search task. We hypothesized that a color maintained in working memory captures attention in a demanding search task only when color is a defining feature of the search target. The MAC effect should not occur when color is irrelevant to the search task set. To verify this hypothesis, we adopted the paradigm that measures the MAC effect with the content maintained in working memory being a singleton distractor in a search task (Olivers et al., 2006) compared with a neutral condition. We recruited two groups of participants in this experiment, with color being relevant to the search task for one group and irrelevant for the other. 2.1. Methods 2.1.1. Participants Thirty-six undergraduate students (n = 18 in each group) at National Taiwan University participated in the experiment for course credit or a NT$120 monetary reward. All participants had normal or corrected-to-normal visual acuity and normal color vision. 2.1.2. Design The experimental design followed a 2 (color relevancy)  2 (trial type) mixed factorial design, with color relevancy as a between-subjects factor and trial type as a within-subjects factor. Participants were randomly assigned to either the color-relevant condition or the color-irrelevant condition. Both groups of participants performed a dual task. They were required to remember a color feature for later recognition and to search for a specific target among colored disks during the maintenance interval. In the color-relevant condition, the search target was a yellow disk with a notch at the top or bottom. In the color-irrelevant condition, the search target was a disk with a notch at the top or bottom. There were two trial types (invalid and neutral) that occurred in a random order with equal frequencies in each condition. In the invalid condition, a color singleton matching the memorized color occurred as a distractor disk; in the neutral condition, the memorized color was not shown in the search array. The MAC effect was measured by the contrast between the invalid and neutral conditions, which reflected the interference caused by the memorized color. 2.1.3. Stimuli All stimuli were presented on a gray background at a viewing distance of 75 cm. A string of ‘‘ABCD’’ or ‘‘1234’’, with 0.2° in height for each alphanumeric stimulus, was presented at the center of the screen for the participants to recite aloud throughout a trial to suppress vocal articulation. The presentation of letters or digits was randomized between trials for each participant. The memory display consisted of one colored disk (a radius of 1.5° visual angle) at the center of the display. The memorized color was randomly chosen from five possible colors (red, orange, green, blue, and purple) in the color-relevant block and from six colors (including yellow) in the color-irrelevant block. The visual search display consisted of nine colored disks with a squared notch (0.5  0.5°) cut out from one of the four sides. The nine disks were equidistantly placed on the rim of an imaginary circle (a radius of 5.3° visual angle). In the color-relevant block, yellow and three other colors randomly selected from the color set (excluding the memorized one) repeated twice in the search array. In the color-irrelevant block, four colors were randomly selected from five colors (excluding the memorized one) to repeat twice

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Fig. 1. An example of the color-relevant condition (top) and color-irrelevant condition (bottom). In the color-relevant condition, participants were required to search for a yellow disk with a squared notch cut out from the top or bottom and to respond to its orientation. In the color-irrelevant condition, participants were required to search for the only disk with a squared notch and to respond to its orientation.

in the search display. The color of the 9th item, the singleton distractor, was the memorized color in the invalid condition and was the 6th unchosen color in the neutral condition. Disks with different colors were randomly placed at the nine possible locations. The color of the recognition probe was randomly chosen under the constraint that the color matched the memorized item in half of the trials and did not match in the other half. 2.1.4. Procedure After signing informed consent, participants were randomly assigned to the color-relevant or the color-irrelevant condition. All participants performed 16 practice and 60 experimental trials. Fig. 1 depicts the sequence of a trial event. Each trial began with a 600 ms display of four numbers or letters. Participants were instructed to recite them out aloud throughout the trial. Thereafter, a colored disk was presented at the center of the screen for 1000 ms. Participants were instructed to memorize the color for later recognition. After a 1500 ms delay, the visual search display, which consisted of nine colored disks, was shown. Participants were required to search for the target disk as quickly and as accurately as possible and to respond to its notch orientation by pressing the ‘‘k’’ key for top or the ‘‘m’’ key for bottom. Following a 500 ms delay, the memory probe was presented and participants had to decide whether the color was identical to the memorized color by pressing the ‘‘z’’ key for same or the ‘‘x’’ key for different. 2.2. Results and discussion Errors in the search task were minimal in both the color-relevant condition (M = 0.42%, SD = 0.87%) and the color-irrelevant condition (M = 1.31%, SD = 1.43%). Performance on memory recognition was high in both the color-relevant (M = 97.28%, SD = 2.54%) and the color-irrelevant conditions (M = 96.50%, SD = 3.19%). In the following analyses, we analyzed the reaction times (RTs) only for correct responses in both the visual search task and the recognition task, and any RTs for the visual search task longer than 2500 ms or shorter than 70 ms were excluded from analysis (6%). Fig. 2 shows mean RTs for the search task. A 2 (condition: color-relevant and color-irrelevant)  2 (trial type: invalid and neutral) mixed-design analysis of variance (ANOVA) showed a significant interaction effect: F(1, 34) = 6.77, p = .01, g2p ¼ :166. This interaction arose because the effect of trial type was significant in the color-relevant condition, F(1, 34) = 27.59, p < .001, g2p ¼ :448, and not in the color-irrelevant condition, F(1, 34) = 2.48, p = .136, g2p ¼ :068. To rule out the role of task difficulty that results from a smaller relevant set size in the color-relevant condition than in the color-irrelevant condition, we used a ratio measure, (invalid–neu tral)/neutral, to reflect the MAC effect in another analysis. The results showed the same pattern that the capture effect is larger in the color-relevant condition than in the color-irrelevant condition, t(34) = 3.33, p = .002, d = 1.110. The MAC effect was observed in the color-relevant condition and not in the color-irrelevant condition. As predicted, the color representation maintained in working memory can bias attention in visual search only when color is a defining feature of the search target. In contrast, the memorized color representation cannot bias attentional allocation when it is irrelevant to the current search task. The finding in the color-irrelevant condition replicates the results of the first experiment in Woodman and Luck’s (2007) study. The MAC effect may not occur when visual search is demanding. 3. Experiment 2 The purpose of this experiment is to investigate whether mindfulness practice can reduce or eliminate TSI compared with two other interventions. Following the instructions used in Dunn, Hartigan, and Mikulas’s study (1999), participants were

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Fig. 2. Mean correct response times (RTs) for the search task as a function of color relevancy and trial type in Experiment 1. Error bars represent standard errors. The black bars show the performance in the invalid condition, and the dark gray bars depict the performance in the neutral condition.

required to sit quietly with eyes closed and to concentrate on deep breathing in mindfulness practice. With this practice, the participants do not receive any external stimulation, focus on internal states moment by moment, disengage from mind wandering whenever it occurs, and sustain their effort on concentration. The second intervention is attentional restoration induced by viewing images of natural scenes. According to the attention restoration theory (Kaplan, 1995; Kaplan, 2001), attention resources can be restored by exposure to nature. Empirical evidence has shown that viewing images of natural scenes can produce cognitive improvements, including increasing working memory capacity and resolving conflict (Berman, Jonides, & Kaplan, 2008). If viewing images of natural scenes can release the mental resources that support cognitive operations, passive viewing of these images may be able to reduce TSI. No prior study has investigated whether viewing images of natural scenes can benefit the reconfiguration of a task set. The third intervention is distraction by engaging participants in a task that is very different from the previous task. In this context, the participants must reload a different task set to accomplish the intervention task. It is likely that reloading a different mental set can overwrite a previous task set. While empirical research has studied distraction as a strategy for emotional regulation (Blair et al., 2007; Erk, Kleczar, & Walter, 2007; Pessoa, McKenna, Gutierrez, & Ungerleider, 2002; Van Dillen & Koole, 2007), no prior study has investigated whether distraction is effective for reconfiguring a task set. On the basis of the results observed in Experiment 1, we required all participants to perform the dual tasks in the first block with color being relevant in the search task. The MAC effect should manifest. Afterward, participants experienced an intervention before the second block in which color is irrelevant to the search task. If the participants continued the same processing mode based on the task set established in the first block, the MAC effect would manifest in the second block. The MAC effect in the second block reflects the TSI. If an intervention is effective for reducing or eliminating the TSI, we should not observe the MAC effect in the second block. 3.1. Method 3.1.1. Participants Forty-eight participants (n = 16 in each group) volunteered in the experiment for course credit or for a NT$120 monetary reward. All participants had normal or corrected-to-normal visual acuity and normal color vision. 3.1.2. Design The experiment consisted of two blocks, a color-relevant block and a color-irrelevant block. The participants performed the color-relevant block first and then performed the color-irrelevant block. The participant’s task was to remember a color patch, search for a target in an array of colored disks, and recognize whether a probe matched the memorized color patch. In the color-relevant block, the search target was a yellow disk with a notch at the top or bottom. In the color-irrelevant block, the search target was a disk with a notch at the top or bottom. In both blocks, the memorized color was irrelevant to the search goal. A color distractor singleton was presented in each search display. In the invalid condition, the color singleton matched the memorized color; in the neutral condition, the memorized color was not presented in the search array. The two conditions occurred with equal frequency within each block. 3.1.3. Stimuli and procedure All stimulus aspects were identical to those of Experiment 1. All participants participated in two blocks of trials. The procedure of Block 1 was identical to the color-relevant condition in Experiment 1, and the procedure of Block 2 was identical to the color-irrelevant condition. Between the two blocks, the participants in different groups were required to perform different tasks for five minutes.

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For the mindfulness practice group, the participants were required to sit quietly with eyes closed and to concentrate on deep breathing for five minutes. The instruction was as follows: ‘‘Please find a comfortable position in which to sit. Over the next five minutes, please close your eyes and concentrate on deep and slow breathing. Try breathing in through your nose and exhaling through your mouth as slowly and deeply as possible. I will measure the time, so please don’t worry about the time limitation. If there are no other questions, please close your eyes and start to take deep breaths.’’ For the scene-viewing group, the participants passively viewed images of natural scenes for five minutes. Each image was displayed once on the screen for 5 seconds, and a total of 60 natural scenes were presented. For the distraction group, participants experienced a localization task. In this task, a display with four white placeholders was presented on the screen for 1000 ms at the beginning of each trial. After this, a white ‘‘O’’, which served as a target, was presented at one of the four possible locations, and a white ‘‘X’’, which served as a distractor, was presented at another. The probability of the target and the distractor being presented at each of the locations was equal. The participants were required to indicate the target location while ignoring the distractor by pressing the spatially corresponding keys on the keyboard. This display was presented on the screen until one of the keys was pressed or for 3000 ms. 3.2. Results and discussion Errors in the search task were minimal (M = 0.82%, SD = 1.46%). Performance on memory recognition was high (M = 96%, SD = 4.36%). In the following analyses, we analyzed the RT data only for correct responses in both the visual search task and the recognition task, and any RTs in the visual search task longer than 2500 ms or shorter than 70 ms were excluded from analysis (6%). A one-way between-subjects design ANOVA was then conducted to examine whether the MAC effect in the first block (color-relevant condition) varied across different intervention groups. The MAC effect was calculated by subtracting the RTs in the neutral condition from the RTs in the invalid condition. The results showed that there was no significant difference in the MAC effect among the three groups, F(2, 45) = 0.53, p = .59, g2p ¼ :023. We also examined whether the three groups differed in the neutral condition of the second block to validate equivalent baseline performance across groups. The results showed a non-significant group effect, p = .399. Fig. 3 shows the MAC effect between the color-relevant block and the color-irrelevant block among the three groups. A 3 (intervention groups: mindfulness, scene-viewing, and distraction)  2 (block type: color-relevant and color-irrelevant)  2 (trial type: invalid and neutral) mixed-design did not show a significant three-way interaction effect (p = .428). Given the prior hypothesis, we conducted an analysis for each group. There was a reliable main effect of block type for all groups, all ps < .001, with faster RTs in the color-relevant block than in the color-irrelevant block. The faster RTs in the color-relevant block arise because the color rule (i.e., search for the yellow disk) constrains the relevant set size to a relatively small number. The validity effect reached significance in all groups (ps < .01). The validity effect showed slower RTs in the invalid condition than in the neutral condition, reflecting the MAC effect and suggesting active maintenance of the memorized color in working memory. The result of interest is the interaction between block type and trial type, which reached significance only in the mindfulness group, F(1, 15) = 6.36, p = .02, g2p ¼ :298. Further analysis showed a significant MAC effect in the color-relevant block, F(1, 30) = 20.85, p < 0.001, g2p ¼ :41; the effect was not significant in the color-irrelevant block, F(1, 30) = 1.06, p = 0.31,

g2p ¼ :034. The results suggested that TSI was eliminated by mindfulness intervention, as the color task set established in the first block did not influence search performance in the second block. The MAC effect, the contrast between the invalid and neutral condition, was 48 ms in the first block and 11 ms in the second block.

Fig. 3. The MAC effect, the interference cost of the invalid condition compared with the neutral condition, in the color-relevant block and color-irrelevant block as a function of intervention type. Bars depict standard errors.

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The scene-viewing and distraction groups showed similar results, with a non-significant interaction effect between block type and trial type, F(1, 15) = 0.07, p = 0.79, g2p ¼ :005 for the scene-viewing group and F(1, 15) < 0.001, p > 0.99, g2p < :001 for the distraction group. For the scene-viewing group, the MAC effect was 48 ms and 48 ms in the first and second block, respectively. For the distraction group, the MAC effect was 64 ms and 56 ms in the first and second block, respectively. The analysis of the ratio scores showed the same pattern of results, suggesting that viewing natural scenes or performing a demanding distraction task does not eliminate the TSI effect. 4. Experiment 3 The objective of this experiment is to investigate whether mindfulness practice eliminates the TSI effect through reconfiguring the mode of attentional control. The TSI effect may reflect continuous adoption of the same control settings established in a previous task set regardless of the change in the task rule. Empirical research has demonstrated the robustness of attentional control settings despite a change in the experimental context, and the effect can be long lasting (e.g., Leber, Kawahara, & Gabari, 2009; Yeh, Lee, Chen, & Chen, 2014). Once a feature is inhibited in performing a task, the inhibitory mechanism continues to operate even when the subsequent task is completely different from the previous one (Moher, Lakshmanan, Egeth, & Ewen, 2014). We verified the hypothesis using scene-viewing intervention as a control. 4.1. Method 4.1.1. Participants Thirty-two participants (n = 16 in each group) volunteered in the experiment for course credit or a NT$120 monetary reward. All participants had normal or corrected-to-normal visual acuity and normal color vision. 4.1.2. Design Participants performed two blocks of trials. In the first block, they were required to memorize a color and then search for a target. A color singleton always occurred in the search display, and it could be the target or a distractor. To introduce a color set in the first block, we manipulated the relation between the memorized color and the search target. In the target-color condition, the memorized red color always predicted the target location. In the distractor-color condition, the memorized green color always occurred at a distractor location. In the neutral condition, the memorized yellow color was uninformative as to the location of a target, with 50% of trials predicting the target location and 50% predicting a distractor location. We expected that the participants would configure a color task set based on the contingency. In the second block, participants performed a letter judgment task. Color was irrelevant to the task, as the letters could occur in any of the three colors. The interest was in whether the participants would be influenced by the irrelevant color according to the color set developed in the first block. If the participants continued using the same color set, we expected that the previous target or distractor color would influence letter judgment in contrast to the neutral color condition. Letter judgment as a function of the color role established in the first block reflects the TSI. 4.1.3. Stimuli All aspects of Experiment 3 were identical to those of Experiment 1 with two exceptions. Only red, green, and yellow colors were used in this experiment. Two letters, ‘‘N’’ and ‘‘Z’’ of 0.57° in height were used in the letter judgment task. 4.1.4. Procedure After signing informed consent, the participants randomly assigned to the two intervention groups first performed the memory-visual search task and then performed the letter judgment task in the second block. There were 16 practice and 240 experimental trials in the memory-visual search task. Fig. 4 depicts the sequence of a trial event. Each trial began with a 600 ms display of four numbers or letters. Participants were instructed to read them out aloud throughout the trial. Thereafter, a colored disk was presented at the center of the screen for 1000 ms. Participants were instructed to memorize the color for later recognition. A visual search display was shown after a 1500 ms delay. Participants were required to search for the target disk with a notch at the top or bottom among eight distractor disks with a notch at the right or left as quickly and as accurately as possible and to respond to its notch orientation by pressing the ‘‘k’’ key for the top or the ‘‘m’’ key for the bottom. Following a 500 ms delay, the memory probe was presented, and participants had to decide whether the color was identical to the memorized color by pressing the ‘z’ key if it was the same or the ‘x’ key if it was different. After performing the memory-visual search task, participants experienced the appropriate intervention for five minutes according to the group to which they were assigned. The procedure and the instructions were identical to those used in Experiment 2 for the scene-viewing group and the mindfulness group. All participants then performed the letter judgment task. A fixation was presented in the center of the screen for 1000 ms. A letter, ‘‘N’’ or ‘‘Z’’, was then presented on the screen center, and the participants were required to indicate which letter was present by pressing the ‘‘n’’ key for the letter ‘‘N’’ or the ‘‘z’’ key for the letter ‘‘Z’’.

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Fig. 4. An example trial of the visual search task (A) and the letter judgment task (B). The search display shows an example for the target-color condition in which the color singleton predicted the location of the search target. In the letter judgment task, the target was printed in red, green or yellow.

4.2. Results and discussion 4.2.1. Task 1: visual search task Errors in the search task were minimal (M = 0.14%, SD = 0.56%). Performance on memory recognition was high (M = 98%, SD = 2.80%). Only correct responses in both the visual search task and the recognition task and the RTs for the visual search task between 70 ms and 2500 ms were included for further analysis. The results from a one-way repeated-measures ANOVA showed that the main effect of the singleton type was significant, F(3, 93) = 413.19, p < .001, g2p ¼ :930. Performance was faster in the target-color condition (629 ms), when the target was in the neutral color (680 ms) rather than in the distractor-color condition (1240 ms) and when a distractor was in the neutral color (1250 ms). The results showed the singleton capture effect (Pashler, 1988; Theeuwes, 1992; Theeuwes, 1994; Theeuwes, 2004), as search was faster when the uninformative yellow singleton was the target, and search was slower when the yellow singleton was the distractor. 4.2.2. Task 2: letter judgment task Accuracy on letter judgment was high (M = 98%, SD = 2.87%). Only the trials with correct letter judgment and the trials with RTs between 70 to 2500 ms were included for further analysis. Fig. 5 shows mean RTs for the letter judgment task. A 2 (intervention groups: scene-viewing and mindfulness)  3 (color type: target, neutral, and distractor) mixed-design ANOVA showed that the main effect of color type was significant, F(2, 60) = 4.46, p = .016, g2p ¼ :129. The performance in the distractor-color condition was slower than that in the target-color condition (p < .05). More importantly, there was a significant interaction between intervention and color type, F(2, 60) = 4.88, p = .011, g2p ¼ :140. This interaction arose because the effect of color type was significant in the scene-viewing group, F(2, 60) = 9.12, p < .001, g2p ¼ :233, and not in the

Fig. 5. Results from Experiment 3. Error bars represent standard errors.

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Fig. 6. Results from Experiment 3. Participants in the mindfulness group were split into two groups depending on their search reaction times. Error bars represent standard errors.

mindfulness group, F(2, 60) = 0.22, p = .806, g2p ¼ :007. For the scene-viewing group, performance in the distractor-color condition was slower than in the neutral-color and the target-color conditions, ps < .001. Given that the overall performance was slower in the mindfulness group, we investigated whether slower performance causes the non-significant TSI. Participants were split into two groups based on their mean RTs: fast and slow. As shown in Fig. 6, there was no significant difference across the three color types for both groups. The interaction between the performance groups (fast and slow) and the color type was not significant, F(2, 28) = 1.37, p = .28, g2p ¼ :089. This null interaction rules out the possibility that the null TSI effect in this group results from slow performance because the overall performance in the fast group was faster than that of the scene-viewing group. The results observed from the scene-viewing group replicated the findings of Moher et al.’s study (2014). The distractor inhibition effect induced from a previous task set was observed in a new task even though the new task was completely different from the previous task. The scene-viewing group showed a TSI effect. In contrast, the carryover effect was no longer observed after 5 minutes of mindfulness practice. This group of participants was able to reset the task rule related to attentional control by releasing the inhibitory processes over the green distractor color. They were able to focus on the current task rule while disengaging from the previous task set. 5. General discussion The goal of the present study was to investigate whether mindfulness practice could effectively reconfigure a previous task set that is irrelevant for achieving a current behavioral goal and whether the alteration of the attentional control mode underlies this effectiveness. The results of Experiment 1 showed the MAC effect only when color was incorporated in the task set necessary to accomplish the search task. In Experiment 2, the participants performed the color-relevant condition in the first block and then performed the color-irrelevant condition in the second block. All participants showed the MAC effect in the first block, suggesting that memorized color maintained in working memory captured attention as a distractor. The result of interest was the manifestation of the MAC effect in the second block after different interventions. After five minutes of viewing images of natural scenes to restore attention or five minutes of distraction by engaging in a different task, participants showed the MAC effect in the second block even when color was irrelevant to the search task. These two groups of participants showed the carryover effect, that is, they showed the task-set inertia effect resulting from continuing mental processes established in the previous task set. In contrast, the participants of the mindfulness practice group who closed their eyes while concentrating on deep breathing did not show the MAC effect in the second block. These participants were able to focus on visual search without interference from the memorized color that was irrelevant to the search task. The results of Experiment 3 further showed that mindfulness was effective because the participants could reconfigure the mode of attentional control established in the previous task set. After viewing images of natural scenes to restore attention, the participants continued the inhibitory processes on a distractor color. As a result, their letter judgment was slower when the letter was printed in the color that consistently predicted a distractor location compared with the neutral condition. In contrast, the participants could release the inhibitory processes in attentional control after five minutes of mindfulness practice. The MAC effect reflects a phenomenon in which people are easily influenced by what is on their mind when external stimuli share visual features with the internal content stored in working memory for a later activity. This scenario occurs in everyday life. The internal representation from the past conscious episode captures attention by default (Han & Kim,

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2009) unless there is a reason to strategically avoid the capture effect (Han & Kim, 2009; Kuo, Chao, & Yeh, 2013; Woodman & Luck, 2007). A reason for avoidance may arise when the stored internal representation impairs current performance or when the internal representation predicted the target in the subsequent task with low probability (Han & Kim, 2009; Kuo et al., 2013; Woodman & Luck, 2007). The results of Experiments 1 and 2 showed that the MAC effect is robust when the search target is defined by color and orientation. In the experimental context, the internally maintained representation never matched the search target and interfered with selection. The participants should have discarded the internal representation when the search display was shown. Yet, the participants could not ignore the capture effect induced by the internal representation stored in working memory. Information that was encoded in a previous conscious moment and that was irrelevant in the present moment captured attention and cost search performance. The carryover of the MAC effect in the second block of Experiment 2 showed that the participants in the scene-viewing and distraction groups continued the operations based on the previous task set even though color was irrelevant to visual search and could interfere with their performance in a demanding search task. Both groups received external stimulation between the two blocks. For the scene-viewing group, the participants had a chance to restore mental resources (Kaplan, 1995; Kaplan, 2001). Yet, the images of natural scenes were chromatic. It is plausible that colors remained relevant during intervention so that the participants continued processing displayed colors even when color was no longer relevant to the search task. They were unable to discard the old rule from the past and reset a new rule in which color played no role in the search task. For the distraction group, it is likely that attentional control was engaged in the localization task during the intervention period so that the participants reactivated the previous processing mode when similar displays were shown in the second block for visual search. In contrast to the scene-viewing and distraction interventions, participants in the mindfulness group received no external stimulation because their eyes were closed. These participants concentrated on deep breathing and orienting their attention to their moment-by-moment experience (Kabat-Zinn, 1990). With a brief period of this practice, the participants were able to focus on the present task in which color was irrelevant to visual search in the second block. Note that this group of participants was accurate on memory recognition (M = 96%, SD = 0.05%), suggesting that they maintained the memorized color in working memory. They were able to focus on the present external stimulation for visual search without interference from the internal representation maintained in working memory. The results of Experiment 3 further revealed that the effectiveness of mindfulness practice results from reconfiguring the mode of attentional control. After a color set is introduced in the first block to link red to the target, green to the distractor, and yellow to a non-informative color, participants inhibited the green color in mental operations. Continuing this mode of attentional control, participants of the scene-viewing group showed slower responses in a simple letter judgment task when the letter was printed in green compared with the conditions in which the letters were printed in red or yellow. In contrast, participants of the mindfulness group did not show this mode of mental operation. The green color was no longer linked to a ‘‘distractor-inhibited’’ tag in attentional control. The participants were able to put aside the past event while concentrating on the present requirement. The effectiveness of mindfulness practice on reconfiguring a task set is in line with the findings in neuroscience that mindfulness improves cognitive control by increasing the structure and functioning of the frontal regions that play a central role in top-down control (Tang, Tang, & Posner, 2013). Mindfulness training also enhanced functional connectivity between the frontoparietal network and the sensory network, which may underlie enhanced sensory processing and attentional focus (Kilpatrick et al., 2011). It is likely that mindfulness practice enables a mental set that adopts an optimal allocation of attentional resources to external stimulation or tasks. Thus, mindfulness meditation can reduce attentional blink (Van Leeuwen, Muller, & Melloni, 2009), reduce Stroop interference (Wenk-Sormaz, 2005), improve performance in a dichotic listening task (Lutz et al., 2009) and enhance discrimination ability (MacLean et al., 2010). If five minutes of mindfulness practice can reconfigure a task set, why were inconsistent results observed in previous studies? Hodgins and Adair (2010) suggested that long-term mindfulness practice enhanced attentional switch. In contrast, three studies showed no significant difference in attentional switch between control and active groups following mindfulness training (Anderson et al., 2007; Chambers et al., 2008; Heeren et al., 2009). Differential degrees of expertise may be one reason for the inconsistent findings. Intertrial switching cost may be another reason for not finding the benefits of mindfulness training on attentional switch. In the studies that showed a null effect from mindfulness training, the change of task rule in each trial may be too frequent for beginners in the active group to exercise the mindfulness practice that they learn during the training phase. It is noteworthy that whether short-term mindfulness practice produces a long-lasting effect remains unclear and the mechanisms for its effectiveness may differ from those that underlie the changes of attentional control in long-term mindfulness practitioners. The current study provided empirical evidence that a short-term mindfulness practice helps to reconfigure a task set and prevents the carryover of a previous mode of attentional control to a subsequent task. A question for future research is whether mindfulness training would produce a long-lasting positive effect on task-set reconfiguration. Another issue remaining to be resolved is whether eye closing is the core of the mindfulness practice that leads to effective reconfiguration of a task set. It is plausible that eye closing is the core given that both the scene-viewing and distraction groups receive external stimulation. We do not take this view because people’s thoughts may wander when they close their eyes, and concentrating on deep breathing can promote attentional focus.

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6. Conclusions The results of the current study showed that task-set inertia is robust, as participants carried a previous color set to a subsequent search or judgment task. Nevertheless, mindfulness practice for five minutes is effective for eliminating task-set inertia. Mindfulness allows one to focus on the present moment without interference from a no-longer relevant feature from the past. The effectiveness appears to result from the ability to reconfigure the mode of attentional control when facing a new task. Thus, five minutes of mindfulness practice may be beneficial for avoiding interference from the mental set activated by recent events when one must focus on the present task. 7. Author contributions Y.-Y. Yeh and C.-Y. Kuo developed the study concept and design. Data was collected and analyzed by C.-Y. Kuo. Both authors interpreted the results. C.-Y. Kuo drafted the manuscript under the supervision of Y.-Y. Yeh, and Y.-Y. Yeh provided critical revisions. All authors approved the final version of the manuscript for submission. Acknowledgments This research was supported by 102-2410-H-002-054-MY2) to Y.-Y. Yeh.

Grants

from

National

Science

Council

(102-2420-H-002-009-MY2

and

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