Introduction

While there is debate concerning its operational definition, mindfulness is often described as a state of non-judgemental and non-elaborative awareness of, and attention to, current external and internal experiences (Bishop et al. 2004; Brown and Ryan 2004; Quaglia et al. 2015). Since the 1970s, several mindfulness-based interventions (MBIs) have been developed with an aim to increase an individual’s tendency to engage in mindfulness (Kabat-Zinn 1990; Segal et al. 2002). These interventions have demonstrated promising results for a wide range of health-related outcomes, such as psychological well-being (Davis and Hayes 2011) and psychopathology (Baer 2003). In contrast to the amount of research that has examined the health-related benefits of MBIs, relatively little research has focused on how these interventions affect basic cognitive processes, such as attention, memory, or learning. To obtain a sense of the disparity, there are at least 26 systematic reviews or meta-analyses that examined the efficacy of MBIs on clinical or health-related outcomes, whereas there is only one meta-analysis that focused exclusively on the impact of mindfulness on cognitive functioning (Chiesa et al. 2011). The disparity highlights a need for examining the underlying mechanisms and cognitive correlates of mindfulness.

The typical length of MBIs is often prohibitive for conducting controlled laboratory-based experiments. Consequently, brief (<30 min) single-session mindfulness exercises are often used to induce a mindful state in the laboratory (e.g. Alberts and Thewissen 2011; Erisman and Roemer 2010), and a handful of researchers have relied upon these exercises to examine how state mindfulness impacts objective measures of cognition, especially attention and memory. For instance, Mrazek et al. (2012) found that an 8-min mindfulness exercise improved performance on a sustained attention task compared to an active reading exercise or a passive rest condition. Lee and Orsillo (2014) found that a 20-min mindfulness exercise reduced reaction times for naming the font colour of both threatening and neutral words in patients with generalized anxiety disorder compared to a mind-wandering control condition. Finally, aside from measures of attention, brief single-session mindfulness exercises can improve cued-recall of English-Swahili word pairs (Bonamo et al. 2015) or impair free recall of emotionally negative words (Alberts and Thewissen 2011), relative to control exercises.

While the above findings suggest that brief single-session mindfulness exercises can improve performance on attention tasks, and influence episodic memory, a recent study has cast doubt on the degree to which these exercises affect cognitive functioning. In Johnson et al. (2015) participants were randomly assigned to a mindfulness condition, a sham mindfulness condition, or a book-listening control condition. Participants in the mindfulness condition listened to 25-min audio recording of mindfulness meditation training, which included attention-to-breathing exercises and an emphasis on a non-judgemental and non-elaborative awareness of current experiences. Following the experimental manipulation, participants completed a self-report measure of state mindfulness and a series of tasks that measure working memory, memory span, and attention. Surprisingly, there were no significant differences among conditions on any of the cognitive measures.

One plausible reason for the inconsistent results described above is that the efficacy of brief single-session mindfulness exercises might be moderated by trait mindfulness. The propensity to engage in mindfulness falls along a continuum in the population, with some individuals demonstrating a natural disposition, whereas others require explicit training and practice (Levesque and Brown 2007). It is reasonable to suppose that a brief single-session mindfulness exercise might not be enough to affect participants who already naturally engage in a mindful state; essentially, these participants might experience a ceiling effect. Alternatively, it is also possible that participants with high trait mindfulness might be more receptive to and involved with a brief exercise compared with low trait mindfulness participants. Consequently, high baseline levels of mindfulness might supplement brief single-session exercises. In either case, it is conceivable that trait mindfulness would influence the efficacy of the exercise. There is some empirical support for this idea: baseline trait mindfulness has been found to moderate the effects of a standard duration MBI on self-report measures of subjective well-being, hope, empathy, and post-intervention trait mindfulness (Shapiro et al. 2011).

From a theoretical standpoint, a state of mindfulness should influence measures of executive attention and recognition memory, as attentional control and inhibition of elaborative processing are key components of current conceptualizations of mindfulness. For instance, Bishop et al. (2004) propose that mindfulness involves the ability to sustain attention on the present moment without elaborating or ruminating on the content of current experiences. In Shapiro, Carlson, Astin, and Freedman’s (2006) theoretical model of mindfulness, a mindful state necessarily involves the improved capacity for self-regulation of attention, and a non-judgemental attitude towards the objects of attention. Along similar lines, Brown et al. (2007) propose that mindfulness involves the attenuation of filters (e.g. cognitive schemas, affective appraisals, and associations with past memories) that act on the present moment, allowing the individual to experience the present qua present. In all of these conceptualizations, the ability to become aware of and attend to the present moment in a non-elaborative and non-judgemental manner is fundamental.

As initially suggested by Bishop et al. (2004), the validity of these conceptualizations could be tested using the Emotional Stroop task (Williams et al. 1996). In this task, participants are visually presented with emotionally arousing (often unpleasant) words and neutral words, and must indicate the font colour of the presented word. Typically there is an increase in reaction time for naming the font-colour of emotional words compared with neutral words. The emotional arousal of unpleasant words is thought to impair attention to the font-colour through a threat-driven generic slowdown in cognitive processing; that is—stimuli which convey a potential threat to well-being (e.g. the word “Kill”), trigger a temporary interruption of on-going activity and a re-direction of cognitive resources to process the potential threat (Algom et al. 2004).

The Emotional Stroop task lends itself well to testing the enhanced attentional control and inhibition of elaborative processing that is thought to characterize a mindful state: If participants are attending to the present moment, while acknowledging the presence of an emotionally arousing word without elaborating or ruminating on the affective content of the word, then reaction times for naming the font colour of emotional words should be similar to those for neutral words. Moreover, recognition memory for the words in the task should also be affected by the mindfulness exercise. It is a well-documented phenomenon that memories for emotionally arousing stimuli are more easily and accurately retrieved compared with neutral stimuli (Kensinger and Corkin 2003). According to the above conceptualizations of mindfulness, a mindful state may serve to reduce the capacity for stimuli to increase emotional arousal and thus attenuate the memory enhancement for emotional words (Alberts and Thewissen 2011).

Examining how brief single-session mindfulness exercises affect measures of state mindfulness, executive attention, and recognition memory in a controlled laboratory setting would refine our understanding of how mindfulness interventions exert cognitive effects, and address which specific domains of cognition are impacted. The results of this study could also prove useful in a clinical context. If a brief single-session mindfulness exercise reduces the impact of emotionally arousing stimuli on attention and memory, then it might serve as an efficient tool to reduce the negative concomitants of affect-based psychopathologies. Furthermore, if the efficacy of the exercise were moderated by trait mindfulness, then clinicians would be better able to adapt the duration of a mindfulness intervention according to the characteristics of their patient.

Thus, the aim of the present study is to determine what effects, if any, a brief mindfulness exercise has on state mindfulness, executive attention, and recognition memory, and to determine if these effects are moderated by trait mindfulness. Three hypotheses were tested. First, we expected that participants in a mindfulness condition would demonstrate greater levels of state mindfulness compared with participants in control conditions. Second, using the Emotional Stroop task, we expected that the difference in reaction time between emotional and neutral words on colour naming would be smaller in a mindfulness condition compared with control conditions. Finally, the difference in recognition accuracy between emotional and neutral words would also be smaller in a mindfulness condition compared with control conditions. For reasons described above, no specific predictions were made in regard to how trait mindfulness might moderate the effects of the brief mindfulness exercise. As such, analyses concerning the moderating effects of trait mindfulness should be considered exploratory.

Method

Participants

Participants were recruited from introductory psychology courses at BLINDED University in exchange for bonus course credit. Expectation effects and demand characteristics were minimized by initially informing participants that the purpose of the study was to examine attention and colour-perception. The total sample included 78 participants, the majority of which self-identified as Caucasian (76 %), and female (78 %), with a mean age of 20.62 years, ranging from 17 to 46 years old. No participants reported any form of colour vision deficiency. Two of 78 participants were removed from the data analysis because they reported previous experience with mindfulness meditation.

Procedure

A 3 × 2 mixed factorial design was employed, with exercise condition (mindfulness vs. attention vs. arithmetic) as a between-subject factor, and word-type (emotional vs. neutral) as a within-subject factor. The participants were randomly assigned to the between-subject conditions, with 26 participants in each condition.

All participants were tested individually. Prior to the experiment proper, each participant completed a brief demographic questionnaire to assess age, handedness, sex, race, meditation experience, and vision problems. Afterwards, each participant completed a self-report measure of trait mindfulness and was then randomly assigned to one of the three exercise conditions. Participants in the mindfulness condition or attention control condition were seated in front of a computer with a blank screen and were instructed to listen to an audio recording and complete the exercises outlined in the audio recording. The audio recording was presented through the computer speakers, and the experimenters were in an adjacent room from the participant during the audio recording. Participants in the arithmetic control condition completed arithmetic exercises for the same duration (10 min) as the audio recordings.

Following the mindfulness, attention, or arithmetic exercise, each participant completed a self-report measure of state mindfulness. Afterwards, they were presented with a computerized version of the Emotional Stroop task. Participants were informed that words in various font-colours would be presented on the computer screen and their task was to simply indicate the font-colour of the word by pressing the appropriate key on the keyboard. Ten emotional and ten neutral words were each presented in red, green, blue, and brown font-colours. The ‘s’, ‘f’,’h’ and ‘k’ keys were labelled with one of the four colours, and the assignment of a colour to a specific key was counterbalanced across participants.

To ensure participants were familiar with the colour-key mapping and understood the instructions for the task, they completed 200 practice trials with coloured letter strings (e.g. “xxxx”). After the practice trials were complete, the experimenter entered the testing room and participants were given the opportunity to ask any questions.

Afterwards, participants completed 80 experimental trials (10 words × 4 colours × 2 word-types), which were blocked according to word-type (McKenna and Sharma 1995). Thus, participants completed 40 trials with neutral words and 40 trials with emotional words. A brief 20-s break separated blocks. The order of blocks was counterbalanced across participants. Within each block, the selection of a particular word/font-colour combination was randomized, with the exception that the same word or font-colour could not appear in two consecutive trials.

Each trial began with the presentation of a fixation cross for 1 s, followed by the presentation of a word. To avoid strategic responding, each word appeared in a pseudo-random location on the screen such that the first letter was always within 40 pixels from the centre of the screen and no two consecutive trials used the same location. Each word remained on screen until the participant depressed one of the four colour keys. Following the release of a key, a fixation-cross appeared for a 1 s inter-trial interval. Reaction time for each trial was measured from the stimulus onset to the depression of a colour key on the keyboard.

Immediately following the Emotional Stroop task, participants completed a 2-min filler task. The task involved counting backwards in steps of three from a number presented on the screen. The number was randomly selected between 1 and 200, and the number would change every 20 s.

Following the filler-task, participants completed a surprise old/new recognition test. Participants were informed that their memory for words on the colour-naming task (i.e. Emotional Stroop) would be tested. They were instructed to use the appropriately marked keys to indicate whether a presented word was “old” or “new”. Old words were defined as those that were presented during the colour-naming task. New words were defined as those that were novel. Participants indicated their response using the ‘v’ and ‘n’ keys, which were labelled as either ‘old’ or ‘new’. The allocation of a key to an ‘old’ or ‘new’ response was counterbalanced across participants.

The recognition test consisted of 40 trials (10 words × 2 word-types × 2 recognition items: old vs. new). On each trial of the recognition test, a fixation cross appeared in the centre of a white screen for 1 s, followed by a word in black font. The selection of each word was randomly determined, and each word appeared on the screen until a participant depressed and released either the ‘old’ or ‘new’ key. A fixation-cross appeared for 1 s during the inter-trial interval. Following the completion of the recognition test, participants were debriefed and left the testing room.

Measures

Trait Mindfulness

Trait mindfulness was measured using the Five-Facet Mindfulness Questionnaire (FFMQ; Baer et al. 2006). The FFMQ contains 39 items and uses a 5-point Likert scale to measure five distinct facets of mindfulness: observing (paying attention to internal and external experiences); describing (the ability to provide labels for inner experiences); acting with awareness (the deliberate attention to one’s actions, as opposed to more automatic behaviour); nonjudging of inner experience (considering one’s cognitions and emotions in a nonjudgmental way); and nonreactivity to inner experience (the capacity for allowing inner experience to come and go without being consumed by them). Each subscale of the FFMQ has adequate-to-good internal consistency, with alpha coefficients ranging from .72 to .92 (Baer et al. 2008).

For a predominantly non-meditating sample, confirmatory factor analyses indicate that the describing, acting with awareness, nonjudging of inner experiences, and nonreactivity to inner experiences facets are components of an overall mindfulness factor (Baer et al. 2006). Thus, the total score across these four facets was used as our measure of trait mindfulness. Cronbach’s alpha for total FFMQ scores in the current sample was 0.79, which is in line with others who relied on a total FFMQ score in non-meditating samples (e.g. de Bruin et al. 2012, α = 0.85).

State Mindfulness

The degree to which the brief single-session mindfulness exercise influenced state mindfulness was assessed using the Toronto Mindfulness Scale (TMS; Lau et al. 2006), which uses 13 items on a 5-point Likert scale to measure two facets of state mindfulness: curiosity (approaching one’s awareness of the present moment with curiosity and desiring to learn more about one’s inner experiences); and decentering (being aware of those thoughts, sensations, and emotions without being carried away by them). The curiosity and decentering facets have good internal consistency, with alpha coefficients of 0.88 and 0.84, respectively (Lau et al. 2006). A participant’s total TMS score was used to measure state mindfulness. Cronbach’s alpha for total TMS scores in the current sample was 0.86.

Stimuli

The ten emotional and ten neutral words selected for the Emotional Stroop task were obtained from McKenna and Sharma’s neutral and emotional word banks (1995, Experiment 2). The words were selected so as to maximize the degree to which they differ in their affective content. In particular, using Whissell’s (2009) Dictionary of Affect in Language, the words were selected on the basis of their pleasantness (unpleasant to pleasant) and activation (passive to active) scores. All emotional words in McKenna and Sharma’s (1995, Experiment 2) word bank were considered unpleasant, but differed in their degree of activity-passivity. We selected the ten emotional words that had the highest activation scores in the emotional word bank. Our ten neutral words had activation scores closest to the mean activation score from McKenna and Sharma’s neutral word bank.

Independent t tests confirmed that the selected ten emotional and ten neutral words did not significantly differ on word length, t(18) = 1.41, p = 0.17, nor frequency, t(18) = .07, p = 0.94, according to Kucera and Francis’ (1967) norms, but did significantly differ on activation, t(18) = 5.63, p < .001, and pleasantness scores, t(18) = 41.17, p < .001, with the emotional words being more active and more unpleasant compared with the neutral words. The ten emotional words were fear, pain, angry, murder, afraid, kill, beaten, fatal, burned, and weep. The ten neutral words were field, lever, league, core, autumn, senior, derive, layer, branch and wagon.

An additional ten neutral and ten emotional words were selected from the McKenna and Sharma (1995) word bank to act as foils on the recognition test. The emotional and neutral foil words did not significantly differ on length, t(18) = 1.411, p = .17, nor frequency, t(18) = 1.854, p = 0.08. The ten emotional foil words were fail, hate, evil, fire, crash, grief, death, cancer, misery, and danger. The ten neutral foil words were gate, clock, thumb, curve, bread, patrol, anchor, exceed, divide, and willow.

All stimuli were presented in size 48, Arial font, on an 18-in. Dell E197FP monitor with 1280 × 1024 resolution. The monitor was positioned 14 in. in front of the participant.

Mindfulness, Attention, and Arithmetic Exercises

Participants in the mindfulness exercise condition listened to a 10-min audio recording of mindfulness meditation. The content of the recording was taken from Erisman and Roemer (2010), and draws from common MBIs. It consists of a description of mindfulness, how mindfulness can be applied to emotional experiences, and guides listeners through two exercises: one which has participants practice mindful awareness of their own breathing, and the other has participants practice mindful awareness of emotions.

Two control conditions were included in this experiment. In the attention exercise control condition, participants listened to a 10-min audio recording on divided and selected attention. The contents were adapted from a cognitive psychology textbook (Sternberg and Sternberg 2009) and supplemented with attention exercises. The first exercise instructed participants to imagine navigating through each room of their childhood home during a hectic family gathering while keeping a mental count of the number of windows in their home. The second exercise involved a continuous bimanual motor task where participants’ left and right hands had to produce two different motor rhythms (i.e. tapping and rubbing) simultaneously. The recording utilized the same voice as in the mindfulness exercise condition. This control condition was selected because it is an active attention task. Much like the mindfulness exercise, participants are instructed to focus their attention; however, the attention exercise does not make reference to a non-judgemental and non-elaborative awareness of the present moment.

In the second control condition, participants were presented with a sheet of arithmetic questions and asked to answer as many questions as possible in a 10-min period. The content of the arithmetic exercise condition made no reference to attention or awareness, allowing for a starker contrast between participants who were exposed to the mindfulness exercises and those who were not.

Data Analyses

One-way and mixed univariate ANOVAs were conducted to determine if exercise condition had any significant effect on total TMS scores, reaction times between emotional and neutral words for correct responses on the Emotional Stroop task, and recognition accuracy between emotional and neutral words on the recognition test. Hierarchical linear regressions with interaction terms (Jaccard et al. 1990) were conducted to assess the degree to which total FFMQ scores moderated the effect of exercise condition on TMS scores, Emotional Stroop performance, and recognition accuracy. In all regression analyses, exercise condition was dummy coded with the mindfulness condition acting as the reference group, and total FFMQ scores were centred. The main effects of exercise condition and total FFMQ scores were always entered in the first block (i.e. main effects only), followed by the interaction terms between an exercise condition dummy variable and total FFMQ scores in the second block. If the change in R 2 between the first and second blocks was significant, then that suggests that the effect of exercise condition on a dependent variable differs at different levels of trait mindfulness (Jaccard et al. 1990).

To tease apart the nature of significant interactions, the data were split into terciles on total FFMQ scores, and separate univariate ANOVAs were conducted for low (i.e. the bottom 33 % of total FFMQ scores), medium, and high levels of trait mindfulness. This is akin to conducting simple slopes analysis in multiple regressions; however, the use of ANOVAs more readily lends itself to interpreting the results as differences among exercise conditions, and between emotional and neutral words. Unless otherwise stated, all assumptions were satisfied and no outliers were present.

Results

To rule out the possibility that any differences among exercise conditions on the dependent variables are simply due to baseline differences in trait mindfulness, we conducted a one-way ANOVA on total FFMQ scores with exercise condition as the between-subject factor. The outcome of ANOVA indicated that there was no significant difference among exercise conditions on total FFMQ scores, F(2,73) < 1, η2 p < 0.01.

State Mindfulness

The effect of exercise condition on state mindfulness was assessed using a one-way ANOVA on total TMS scores. It should be noted that the same pattern of results emerges when analysing each sub-scale of the TMS separately. The assumption of homogeneity of variance was violated. Consequently, a Brown-Forsythe correction was used. The corrected one-way ANOVA revealed a significant effect of exercise condition, F(2,61.97) = 19.75, p < 0.001, η2 p = 0.35. Games-Howell post hoc tests revealed that total TMS scores were significantly greater in the mindfulness (M = 31.65, SD = 7.34) and attention (M = 32.80, SD = 5.07) conditions compared with the arithmetic condition (M = 21.08, SD = 8.93). A hierarchical linear regression was conducted to assess the degree to which trait mindfulness moderated this effect. The results of the regression revealed that the change in R 2 between the first and second blocks was not significant, ΔF(2,70) = 2.73, p = 0.07, ΔR 2 = 0.05. Taken together, these results suggest an attention exercise and a brief mindfulness exercise can improve state mindfulness compared to an arithmetic control condition, and that this effect is not moderated by trait mindfulness.

Emotional Stroop Performance

The effect of exercise condition on Emotional Stroop performance was assessed using a 2 (word-type: Emotional vs. Neutral) × 3 (exercise condition: Mindfulness vs. Attention vs. Arithmetic) mixed ANOVA, with word-type as the within-subject factor. Four participants were identified as outliers (Z > 2.50) and were removed from subsequent analyses of Emotional Stroop performance. The mixed ANOVA revealed a significant main effect of word-type, F(1,69) = 4.26, p = 0.041, η2 p = 0.06, with greater reaction times for emotional words (M = 735.44, SD = 124.51) compared with neutral words (M = 721.09, SD = 121.69). This result indicates that the Emotional Stroop effect was replicated in the current experiment. The main effect of exercise condition, F(2,69) < 1, and the interaction between word-type and exercise condition F(2,69) = 1.73, p = 0.18, were not significant.

To determine if the relationship between exercise condition and the Emotional Stroop effect was moderated by trait mindfulness, a difference score was calculated between reaction times for emotional and neutral words, and entered as the dependent variable in the hierarchical regression analysis. Three participants were identified as multivariate outliers and were removed from the analysis. The overall regression model with interaction terms was statistically significant, F(5,68) = 2.66, p = 0.03, R 2 = 0.17. The R 2 change between the first and second blocks was also statistically significant, ΔF(2,63) = 4.49, p = 0.011, ΔR 2 = 0.13, which indicates that trait mindfulness moderates the relationship between exercise condition and the Emotional Stroop effect.

To tease apart this interaction, the data were split into terciles on total FFMQ scores, and follow-up 2 (word-type) × 3 (exercise condition) mixed ANOVAs were conducted for low, medium, and high levels of trait mindfulness. The results are presented in Fig. 1. For participants with low levels of trait mindfulness, the main effect of word-type, F(1,21) = 6.13, p = 0.02, η2 p = 0.23, and the word-type × exercise condition interaction, F(2,21) = 8.02, p = 0.003, η2 p = 0.43, were significant. Simple main effects analysis revealed that difference in reaction times between emotional and neutral words was significant in the attention control condition, F(1,21) = 20.35, p < 0.01, but not in the mindfulness condition, F(1,21) < 1, nor in the arithmetic control condition, F(1,21) < 1. For participants with either medium or high levels of trait mindfulness, the word-type × exercise condition interactions were not significant, F(2,19) = 1.86, p = 0.18, and F(2,20) < 1, respectively. The main effect of word-type was significant for high trait mindfulness participants, F(1, 20) = 6.42, p = 0.02, η2 p = 0.24, but not for medium trait mindfulness participants, F(1,19) < 1. These results suggest that, relative to an attention control condition, a brief mindfulness exercise can improve executive attention on a colour-naming task in the presence of emotionally arousing stimuli, but only for participants with low levels of trait mindfulness.

Fig. 1
figure 1

Mean reaction time for colour-naming emotional and neutral words across exercise conditions and trait mindfulness terciles. Error bars represent 1 SEM. The p values for low trait mindfulness participants reflect the simple main effects of word-type for each level of exercise condition. The p value for high trait mindfulness reflects the main effect of word-type

Full size image

Recognition Memory

Eight participants were outliers on mean recognition accuracy for neutral or emotional words, and were removed from subsequent analyses of recognition memory. A 2 (word-type) × 3 (exercise condition) mixed ANOVA was conducted on mean recognition accuracy. The results revealed a significant main effect of word-type, F(1,65) = 48.99, p < 0.001, η2 p = 0.43, whereas the main effect of exercise condition and the word-type × exercise condition interaction were not significant, F(2,65) = 1.03, p = 0.36, and F(2,65) < 1, respectively. A greater proportion of emotional words (M = 0.92, SD = 0.08) were correctly recognized compared with neutral words (M = 0.72, SD = 0.23). To assess if trait mindfulness moderated these findings, a difference score between mean recognition accuracy for emotional words and neutral words was entered as the dependent variable in the hierarchal regression analysis. The change in R 2 between the first and second blocks was not significant, ΔF(2,62) < 1, which suggests that trait mindfulness does not moderate the relationship between exercise condition and recognition memory accuracy.

Discussion

Brief single-session mindfulness exercises are increasingly being used to examine the cognitive correlates of mindfulness in a controlled laboratory setting. We investigated the degree to which one of these exercises affect measures of state mindfulness, executive attention, and recognition memory, and whether the efficacy of the exercise is moderated by trait mindfulness.

First, we predicted that a 10-min single-session mindfulness exercise would increase levels of state mindfulness, as measured by total TMS scores, compared with an attention exercise or arithmetic exercise. Our results yielded mixed support for this hypothesis. On the one hand, total TMS scores were greater in the mindfulness exercise condition compared with the arithmetic exercise condition, which is consistent with our prediction and provides additional support for previous studies that used brief single-session mindfulness exercises to induce a state of mindfulness (e.g. Alberts and Thewissen 2011; Erisman and Roemer 2010). On the other hand, total TMS scores in the attention exercise condition were greater than the arithmetic exercise condition and did not significantly differ from the mindfulness exercise condition. Considering that the efficacy of the exercises at inducing a state of mindfulness was not moderated by trait mindfulness, and that baseline total FFMQ scores did not significantly differ across exercise conditions, it is unlikely that these results are simply be due to pre-existing differences in trait mindfulness across conditions.

The content of the attention and mindfulness exercises was similar insofar as both instructed participants to focus their attention on a particular item (i.e. breathing and the present moment in the mindfulness exercise compared with their childhood home and a bimanual motor task in the attention exercise). This shared emphasis on controlling attention could help explain why total TMS scores were similar in the attention and mindfulness exercise conditions. In support of this possibility, Johnson et al. (2015) found that total TMS scores did not significantly differ between a 25-min mindfulness exercise condition and a sham mindfulness control condition that included attention-to-breathing exercises. Taken together, these findings suggest that brief mindfulness exercises per se are not exclusively capable of increasing levels of state mindfulness. The relationship between mindfulness and attention could be bi-directional, such that effortful control of attention could increase state mindfulness. Alternatively, these findings could reflect a lack of the TMS’ sensitivity at distinguishing between enhanced attentional control in and of itself and mindfulness, or simply a type II error. More research is necessary to demarcate these possibilities.

According to current conceptualizations of mindfulness, a mindful state partly involves enhanced attentional control and inhibition of elaborative processing (Bishop et al. 2004; Brown et al. 2007; Shapiro et al. 2006). In support of this and our second hypothesis, we found less emotional interference on a colour-naming task following a brief mindfulness exercise compared with an attention exercise. However, the salutary effects of mindfulness were only apparent for those with low trait mindfulness. While this finding is tempered by the fact that we investigated the moderating effects of trait mindfulness in an exploratory manner, it nonetheless raises the question as to why the impact of a brief mindfulness exercise on executive attention is more salient for those who are not naturally predisposed to be mindful? Higher levels of trait mindfulness are associated with greater performance on attention tasks (Moore and Malinowski 2009) and greater neural activity in attention networks (Dickenson et al. 2013). Consequently, participants with low levels of trait mindfulness might have more to gain from the brief mindfulness exercise compared with their high trait mindfulness counterparts.

One may wonder why we found a significant difference between mindfulness and attention conditions on Emotional Stroop performance even though both conditions were similar on total TMS scores. We propose that the effects of the mindfulness exercise on executive attention were over and above those on the self-report measure of state mindfulness. While the attention exercises may have prompted participants to be more aware and exert greater control over their attention, which is associated with greater TMS scores (Lau et al. 2006), it is unlikely that the exercise would instantiate the same degree of inhibition of elaborative processing as the mindfulness exercise. Consequently, emotional words were more disruptive to colour-naming in the attention exercise compared with the mindfulness exercise.

The moderating effects of trait mindfulness could help explain the inconsistent results across studies that used brief single-session mindfulness exercises to probe the attention correlates of mindfulness. In some cases, random assignment might minimize individual differences in trait mindfulness, which could explain why some studies reported positive effects (Mrazek et al. 2012; Lee and Orsillo 2014), but in other cases, randomization might not completely control for these individual differences, which would obscure any effects (Johnson et al. 2015). Future research that relies on brief single-session mindfulness exercises should consider including a measure of trait mindfulness as a covariate.

It should be noted that a similar pattern of inconsistent results emerges from studies that investigated the impact of standard duration or shortened versions of MBIs on measures of attention (Chiesa et al. 2011). While we are cautious to generalize our findings to situations where standard duration MBIs are employed, our results nevertheless suggest that the aforementioned inconsistencies might be partly due to differences in trait mindfulness.

Finally, while we were able to reproduce the memory enhancement for emotional words over neutral words (Kensinger and Corkin 2003), we were unable to attenuate this effect using a brief mindfulness exercise. Thus, our third hypothesis was not supported. Our findings are in contrast to the results of Alberts and Thewissen (2011), who found that a brief mindfulness exercise decreased recall accuracy for unpleasant emotional words compared with a control condition. Overlearning might be responsible for our failure to detect any mindfulness effects on recognition memory. In Alberts and Thewissen, each word was presented once, studied for 2 s, and a 20-min retention interval separated the study period from a delayed-recall test. Whereas in the present study, each word was presented four times, remained on the monitor until a participant made a response, and a 2-min retention interval separated study from test. As a result, overall recognition performance for emotional words was quite high (<0.90), which might have masked subtle differences in memory performance across exercise conditions.

A few limitations of the present study should be noted. First, we did not control for participants’ mood or anxiety, which can affect performance on the Emotional Stroop task (Richards et al. 1992). While reaction times were significantly greater for emotional words compared with neutral words collapsing across exercise conditions, the effect size was small (η2 p = 0.06), and negligible for participants with medium levels of trait mindfulness (see Fig. 1). Individual differences in mood or anxiety may be contributing to this pattern of results, and future studies using the Emotional Stroop paradigm as a measure of executive attention should take these variables into account.

Second, the generalizability of our findings is weakened by the fact that the influence of the brief mindfulness exercise on executive attention was only apparent when contrasting the mindfulness condition with only one of our control conditions. Surprisingly, there was no significant difference between the mindfulness exercise condition and the arithmetic exercise condition on Emotional Stroop performance. The fact that our sample consisted primarily of female undergraduate students also limits the conclusions that can be drawn. Additional research with male participants and alternative control conditions would be useful for testing the strength of our findings.

Finally, trait mindfulness was operationally defined as a total score across four of the five facets of the FFMQ. While these four facets are thought to capture an overarching mindfulness construct in non-meditating samples, a recent psychometric validation study (Park et al. 2013) call into question the use of a total score on the FFMQ. Future studies that use the FFMQ to operationalize trait mindfulness should make an informed decision as to which specific facets best capture trait mindfulness.

In closing, our results highlight the complex relationship between brief mindfulness exercises and cognitive processes. We found that an exercise that requires effortful control of attention can affect self-reported state mindfulness to the same degree as a brief mindfulness exercise. Furthermore, we found evidence to suggest that trait mindfulness can moderate the efficacy of a brief mindfulness exercise at reducing emotional interference on a task of executive attention. Additional work is necessary to corroborate or discount this finding. In order to better increase our understanding of the cognitive correlates of mindfulness, future studies that use brief mindfulness exercises in randomized designs should carefully consider the nature of their control conditions and take into account the state and trait qualities of mindfulness.