2019-2020 Doctoral Awardee: Nur Hani Zainal

“A Randomized Controlled Trial of a 14-Day Mindfulness Ecological Momentary Intervention for Generalized Anxiety Disorder”

Nur Hani Zainal, The Pennsylvania State University, Department of Psychology


Little is known about how brief mindfulness therapies (MT) enhance cognitive abilities in clinical samples. Relatedly, no prior brief, smartphone mindfulness ecological momentary intervention (MEMI) has targeted generalized anxiety disorder (GAD). Moreover, although theories propose that MT can boost executive functioning and subjective attentional control (SAC), they have largely gone untested. Thus, this randomized controlled trial (RCT) assessed the efficacy of a 14-day smartphone MEMI (vs. self-monitoring placebo [SMP]). MEMI participants exercised multiple core mindfulness strategies (open monitoring, acceptance, attending to small moments, slowed rhythmic diaphragmatic breathing), and were encouraged to practice mindfulness throughout life. Comparatively, SMP participants were prompted to practice self-monitoring (noticing their thoughts and rating any associated distress). All prompts occurred 5 times a day, for 14 consecutive days. Twenty-one MEMI and 17 SMP participants (M = 20.79 years, 84.21% females) completed neuropsychological tests at baseline, post-treatment, and 1-month follow-up. MEMI (vs. SMP) participants showed large significant improvement in SAC – focusing (d = 0.80), but not shifting (d = 0.003). Also, MEMI (vs. SMP) had small-to-moderate pre-post effects on performance-based working memory (d = 0.20), processing speed (d = 0.25), inhibition (d = 0.29), and verbal fluency (d = 0.56). Maintenance of gains were observed from post-treatment-to-1-month-follow-up.


Mindfulness is referred to as the effortful and continual process of focusing on experiences in the here-and-now in flexible, curious, and receptive ways (Bishop et al., 2004). Mindfulness-based interventions (MBIs) have been designed over the past 40 years to boost diverse mindfulness and related skills (Kabat-Zinn et al., 1992). MBIs equip persons with various complex techniques such that, practicing attentional and emotion regulation tactics, promotes psychological health, emotional stability, and cognitive flexibility (Lippelt, Hommel, & Colzato, 2014; Lutz, Slagter, Dunne, & Davidson, 2008). Advancing our understanding of MBIs is thus essential to benefit the socio-cognitive, clinical, and organizational sciences.

Recently, theories such as the mindfulness-cognitive enhancement (Chiesa, Calati, & Serretti, 2011) and mindful emotion regulation (Teper, Segal, & Inzlicht, 2013) models, propose that MBIs can enhance executive functioning (EF) and related cognitive domains. Supporting some aspects of these theories, data across 29 case-control and pre-post studies (n = 1,777) showed that mindfulness practice intensity was moderately correlated with attention (r = .28), global cognition (r = .28), and memory (r = .21) (Sedlmeier et al., 2012). However, how MBIs impact other unique cognitive domains (e.g., subjective attentional control, processing speed, verbal fluency, EF dimensions such as working memory [WM], shifting, and inhibition) remains open to inquiry. Also, unlike randomized controlled trials (RCTs), case-control and open-trial studies do not establish causality (Shadish, Cook, & Campbell, 2002). As open-trial studies do not include a control condition, effects due to history, maturation, and regression to the mean cannot be ruled out. Also, most prior MBI RCTs assessing impact on cognitive functioning recruited healthy controls (Lao, Kissane, & Meadows, 2016); thus, findings might not extend to clinical samples.

Accordingly, this RCT addressed these gaps by assessing the efficacy of a 14-day smartphone mindfulness ecological momentary intervention (MEMI) (vs. self-monitoring placebo [SMP]) in undergraduates and community-dwelling adults with generalized anxiety disorder (GAD). Participants were instructed to engage in different techniques, 5 times a day, for 14 consecutive days. MEMI participants exercised core mindfulness strategies (open monitoring, acceptance, attending to small moments, slowed rhythmic diaphragmatic breathing). Also, MEMI participants were given daily reminders before bedtime to practice mindfulness continually in between prompts and after treatment ends. Comparatively, SMP participants were instructed to notice their thoughts and rate any distress associated with them. They were not taught any mindfulness strategies. All participants completed a GAD severity self-report and neuropsychological assessments at baseline, post-treatment, and 1-month follow-up. Including objective and subjective cognitive ability measures to test the impact of MBIs on EF and related capacities across baseline, post-treatment, and follow-up is essential as performance-based cognitive tests and self-reports of cognitive abilities might not correlate highly with one another. Also, MBI RCTs to date rarely include a follow-up (Chiesa et al., 2011); thus, maintenance of any cognitive gains derived from MBI RCTs remains under-investigated.


Thirty-eight participants with GAD were randomly assigned to either MEMI (n = 21) or SMP (n = 17). Participants averaged 20.79 years, 84.21% were females, and 68.42% identified as White. These participants met criteria for GAD based on the Diagnostic and Statistical Manual–Fifth Version (DSM-5; American Psychiatric Association, 2013) and Generalized Anxiety Disorder Questionnaire–Fourth version (GAD-Q-IV) self-report (Newman et al., 2002). High level of inter-rater agreement among rigorously trained undergraduate and master’s-level assessors have been established for the GAD diagnosis (κ = .97, p < .001). Moreover, participants were at least 18 years of age, own an iPhone or Android phone, and provided informed consent. Exclusion criteria included presence of suicidality, mania, psychosis, or substance use disorders.

Attentional Control and Executive Functioning Measures

Attentional Control Questionnaire (ACQ; Derryberry & Reed, 2002). Participants rated a 20-item self-report on the capacity to concentrate and switch attention when required.  Whereas 9 items captured attentional focusing, 11 items tapped into attentional shifting. For each item, respondents endorsed on a 4-point Likert scale (0 = almost never to 3 = always).

Working Memory (Wechsler, 2008). WM was tested with four Wechsler Adult Intelligence Scale–Fourth Edition (WAIS-IV; Wechsler, 2008) subtests: digit span (DS) forward; DS backward; DS sequencing; letter-number sequencing (LNS). Participants reiterated increasingly longer number strings verbatim (DS Forward), backwards (DS Backward), or in ascending order (DS Sequencing). LNS requires recalling and rearranging lengthier alphanumeric strings in ascending numerical and alphabetical order.

Color-Word Interference Test (CWIT; Delis, Kaplan, & Kramer, 2001). The CWIT from the Delis-Kaplan Executive Functioning System (D-KEFS; Delis et al., 2001) was used to measure inhibitory control ability. The Inhibition/Switching condition sets it apart from other versions of Stroop tests. In this condition, participants said the word ink color; however, for words displayed in outlined boxes (a situational cue), they said the word instead.

Controlled Oral Word Association Test (COWAT; Borkowski, Benton, & Spreen, 1967). The COWAT is a three-subtest verbal fluency measure of word production within a 1-minute time limit. Participants were assessed in a phonemic format requiring strenuous effort (Letter Fluency) and via highly learned concepts (Category Fluency). Also, they had to fluidly switch between distinct overlearned concepts (Category Switching).

Trail Making Test (TMT; Army Individual Test Battery, 1944). TMT, a two-part assessment, measured cognitive flexibility. First, Part A (TMT-A) required drawing to connect digits from 1 to 25 consecutively, and Part B required sequentially connecting digits and alphabets in an alternating way (i.e., 1-A-2-B, etc.). Faster response time on the TMT-A and TMT-B indexed better motor processing speed and set-shifting respectively.

Planned Analyses

Piecewise multilevel modeling (MLM) analyses were conducted to account for nesting of repeated measures within persons, and persons clustered within treatment groups, with the R package lme4 (Bates, Maechler, & Bolker, 2012). Distinct analyses were performed for each of the outcome variables from pre-to-post-treatment and post-treatment to 1-month follow-up. We assumed random intercepts and slopes for all models. Whereas Level 1 modeled within-person changes over time, Level 2 modeled between-person factors. Cohen’s d effect size was computed where 0.2, 0.5, and 0.8 denoted small, moderate, and large effects, respectively (Cohen, 1992).


Baseline Group Differences

            There were no significant pre-treatment differences between MEMI and SMP for all of the treatment outcome measures, with negligible-to-small effect sizes: GAD-Q-IV (d = -0.15), ACQ Focusing and Shifting components (average d = -0.35), WAIS-IV WM DS Forward, DS Backward, DS Sequencing, and LNS subtests (average d = 0.05), CWIT Inhibition/Switching subtest (average d = 0.03), COWAT Letter, Category, and Category Switching subtests (average d = 0.21), and TMT Part A and Part B (average d = -0.09).

Symptom and Cognitive Outcome Measures

            Trait Worry. For GAD-Q-IV continuous score as the outcome, MEMI (vs. SMP) had a moderate effect (d = 0.48), showing greater reduction in GAD severity for MEMI participants from pre-to-post treatment. This gain was maintained from post-treatment to 1-month follow-up.

            Subjective Attentional Control. Compared to SMP, MEMI had a large significant effect on ACQ – Focusing (i.e., attending to an object in one’s field of awareness) (d = 0.80), but not ACQ – Shifting component (i.e., switching from one mental set to another) (d = 0.003) from pre-to-post-treatment. The gain for ACQ – Focusing was maintained from post-to-follow-up.   

            Working Memory. Relative to SMP, MEMI had negligible to small positive pre-to-post-treatment effect on each of the distinct WAIS-IV WM subtests: DS Forward (d = 0.08), DS Backward (d = 0.20), DS Sequencing (d = 0.38), and LNS (d = 0.37). The small-to-moderate gains for DS Backward, DS Sequencing, and LNS either retained or continued to enhance from post-treatment to 1-month follow-up.

            Inhibition. From pre-to-post-treatment, MEMI (vs. SMP) participants showed a small positive effect for CWIT – Inhibition/Switching (d = 0.29). From post-treatment to 1-month follow-up, the gain observed for CWIT – Inhibition/Switching persisted.

            Verbal Fluency (Cognitive Flexibility). For verbal fluency (i.e., number of words produced within one minute for words starting with specific letters [F, A, and S] or representing a semantic category), MEMI consistently had a strong positive moderate effect for COWAT – Letter Fluency (d = 0.56) and COWAT – Category Fluency (d = 0.51) compared to SMP, from pre-to-post-treatment. On the other hand, MEMI (vs. SMP) had small positive pre-to-post-treatment effect for COWAT – Category Switching – Total (Correct and Incorrect) Responses (d = 0.20) and COWAT – Category Switching – Correct Responses (d = 0.27). Observed treatment gains for the verbal fluency subtests were sustained or continued to enhance post-to-follow-up.

            Shifting. For TMT Part B as the outcome, the effect of MEMI was negligible relative to SMP (d = 0.03) from pre-to-post treatment. However, from post-treatment to 1-month follow-up, MEMI (vs. SMP) had a moderate positive effect on shifting as indexed by the TMT Part B.

            Processing Speed. For TMT Part A as the outcome, MEMI had a small pre-to-post-treatment effect relative to SMP (d = 0.25). The impact of MEMI (vs. SMP) on processing speed marked by TMT Part A continued to improve from post-treatment to 1-month follow-up.


Offering some support to the mindfulness-cognitive enhancement (Chiesa et al., 2011) and mindful-emotion regulation (Teper et al., 2013) theories, recipients of the 14-day self-help MEMI (vs. SMP) showed large gains in subjective attentional control – focusing component, moderate beneficial effects on letter and semantic (categorical) verbal fluency, as well as small positive effects on WM, inhibition, and processing speed. Analyses also revealed that compared to SMP, MEMI had negligible effects on subjective attentional control – shifting component as well as performance-based shifting measured by the TMT Part B. Simultaneously, MEMI (vs. SMP) had moderate effect on reducing GAD severity throughout all time-points.

Why did MEMI induce positive small-to-large benefits on self-reported focusing as well as performance-based verbal fluency (also a marker of cognitive flexibility), inhibition, WM, and processing speed relative to SMP? One tenable account is that mindfulness practices via the MEMI cultivates improvement in observational skills as well as non-judgmental acceptance of external and internal events. Relatedly, findings lend support to cognitive theories (Langer, 2017; Sternberg, 2000) which propose that habitually grounding oneself to the here-and-now and being open to new experiences likely enhances the ability to mentally monitor and alter environmental inputs. To this end, continual mindfulness practices prompted by the MEMI might have enhanced multiple distinct cognitive abilities by safeguarding one from getting preoccupied with physiological sensations, feelings, and thoughts, and to instead concentrate on the task-at-hand.

Noteworthy was that the pattern of findings herein largely concurs with and extends prior MBIs in healthy student and community-dwelling adult as well medically ill samples. For instance, previous RCTs showed that MBIs reduced self-reported mind-wandering and enhanced subjective attentiveness as well as behavioral indices of WM accuracy (Mrazek, Franklin, Phillips, Baird, & Schooler, 2013) and sustained attention (Semple, 2010) in healthy young adults, as well as inhibition (Johns et al., 2016) and processing speed (Richard et al., 2019) in middle-aged patients recovering from breast cancer and stroke. At the same time, the mostly negligible effect of MEMI on subjective and objective markers of shifting are in concordance with one of the most well-designed RCTs to date (Jensen, Vangkilde, Frokjaer, & Hasselbalch, 2012). In that study, mindfulness-based stress reduction conferred greater advantages than relaxation training or motivated (incentivized) condition on post-treatment WM accuracy and sustained attention, but no comparative benefit on behavioral measures of shifting.

Study limitations deserve mention. Given the small sample size of the current study, future well-powered, replication efforts are needed to clarify the pattern of results. Also, as this study comprised mostly young White females, upcoming investigations could recruit culturally- and age- diverse samples to test generalizability of findings. Nonetheless, the current RCT is the first to examine the effect of a brief, technology-assisted MBI on multiple cognitive domains in pathological worriers. Future RCTs could add neural measures to test if any MBI-derived cognitive benefits might coincide with decrements in resting-state default mode network activity linked to mind wandering tendencies and strengthen EF-affiliated brain regions (Malinowski, 2013) in GAD or other related anxiety or depressive disorders.

Impact Statement

            The field of public health, clinical, and cognitive sciences can benefit from a broader and deeper understanding of whether and how mindfulness-based interventions (MBIs) enhance unique cognitive domains, such as basic attentional regulation and higher-order executive functioning. Further, despite theories proposing that MBIs could improve a variety of cognitive domains, there remains a dearth of rigorous randomized controlled trials (RCTs) testing these models, clarifying the specific cognitive domains impacted by MBIs, and their effects in clinical samples. Accordingly, this current RCT shows that a 14-day smartphone-delivered mindfulness ecological momentary intervention (versus self-monitoring placebo) had small-to-large effects on self-reported focusing and performance-based measures of working memory, inhibition, set-shifting, processing speed, and verbal fluency in persons with generalized anxiety disorder, with benefits either persisting or continuing to improve one month after treatment completion. If findings herein are replicated, introducing ambulatory MBIs in diverse contexts could alleviate distress and enhance a range of cognitive skills in psychologically distressed samples.


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