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‘‘Mind the Trap’’: Mindfulness Practice Reduces Cognitive
Rigidity
Jonathan Greenberg*, Keren Reiner, Nachshon Meiran
Department of Psychology, Ben-Gurion University of the Negev, Beer-Sheva, Israel
Abstract
Two experiments examined the relation between mindfulness practice and cognitive rigidity by using a variation of the
Einstellung water jar task. Participants were required to use three hypothetical jars to obtain a specific amount of water.
Initial problems were solvable by the same complex formula, but in later problems (‘‘critical’’ or ‘‘trap’’ problems) solving
was possible by an additional much simpler formula. A rigidity score was compiled through perseverance of the complex
formula. In Experiment 1, experienced mindfulness meditators received significantly lower rigidity scores than non-
meditators who had registered for their first meditation retreat. Similar results were obtained in randomized controlled
Experiment 2 comparing non-meditators who underwent an eight meeting mindfulness program with a waiting list group.
The authors conclude that mindfulness meditation reduces cognitive rigidity via the tendency to be ‘‘blinded’’ by
experience. Results are discussed in light of the benefits of mindfulness practice regarding a reduced tendency to overlook
novel and adaptive ways of responding due to past experience, both in and out of the clinical setting.
Citation: Greenberg J, Reiner K, Meiran N (2012) ‘‘Mind the Trap’’: Mindfulness Practice Reduces Cognitive Rigidity. PLoS ONE 7(5): e36206. doi:10.1371/
journal.pone.0036206
Editor: Leonardo Fontenelle, Institute of Psychiatry at the Federal University of Rio de Janeiro, Brazil
Received November 20, 2011; Accepted April 2, 2012; Published May 15, 2012
Copyright: ß2012 Greenberg et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The work was partly supported by a research grant to the third author from the Israel Science Foundation. The funders had no role in study design,
data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding received for this study.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: greenbej@bgu.ac.il.
Introduction
Experience may blind us from recognizing obvious solutions to
problems. Research shows that physicians and health care
professionals are likely to overlook the correct diagnosis in cases
which do not match their experience [1]. Similar findings have
been reported concerning difficulties in reframing clinical situa-
tions as experienced by healthcare professionals [2,3], and
difficulties of managers and decision makers in replacing existing
procedures with new, improved and simpler ones [4]. This
‘‘blinding’’ to novel solutions may be considered a form of
cognitive rigidity, which has commonly been defined as a resistance
to change in beliefs, attitudes or personal habits [5], or the
tendency to develop and perseverate in the use of mental or
behavioral sets [6].
Such cognitive rigidity may play a key role in psychopathlogy
(for reviews see [6,7], see also [8]). It has been closely linked to the
inability of suicidal individuals to consider alternatives that may be
accessible to another person [9,10], as well as to rumination,
a major risk factor of depression [11]. Similar forms of cognitive
rigidity were also indicated in obsessions [12,13], alcohol de-
pendence [14], eating disorders [15], and Attention Deficit
Disorder [16–20]. In this paper, we propose that mindfulness
meditation may provide a means of decreasing the aforementioned
type of cognitive rigidity.
Mindfulness is a term which has developed from early eastern
traditions and has been commonly defined as "paying attention in
a particular way: on purpose, in the present moment and non-
judgmentally’’ [21]. Although some have directly linked mindful-
ness to a practice of meditation (e.g. [22–24]), others (e.g. [25–27])
have referred to it as rather independent from meditation practice.
Mindfulness has additionally been described as a theoretical
construct, a psychological process [28], and a trait (see [29,30] for
a recent discussion of discrepancies between various definitions of
mindfulness). Nevertheless, mindfulness has been commonly
claimed to involve regulation of the focus of attention towards
the current experience, a willingness to come in contact with and
be receptive to experience rather than avoid it or cope by means of
repression, and to involve adopting a ‘‘beginners mind’’ and seeing
things in a ‘‘fresh’’ way [31]. These last attributes of mindfulness in
particular seem to potentially immune one from being blinded by
experience.
Mindfulness has received a great deal of empirical attention
over the last three decades, and various psychotherapeutic
techniques based on mindfulness have been developed (e.g.
[22,32,33]). Mindfulness based interventions have been shown to
alleviate symptoms of a variety of clinical conditions such as
suicidal ideation and manic symptoms [34], relapse reduction in
recurrent major depression (see [35–37] for recent reviews),
rumination ([38,39] see [40] for differential effects of mindfulness
on adaptive and maladaptive rumination), addictions and sub-
stance use disorders [41,42], eating disorders (see [43] for a review),
generalized anxiety [44], obsessive compulsive disorder (OCD)
[32], and attention deficit/hyperactivity disorder (ADHD) [45].
Interestingly, many of the disorders which benefit from mindful-
ness mediation are also characterized by some form of rigidity,
suggesting that the efficacy of mindfulness may perhaps be
mediated by reduced rigidity.
In addition to studying mindfulness as a form of therapeutic
intervention, there has been a growing body of research over the
last years examining various cognitive abilities related to mindful-
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ness, most of which focusing on various measures of attention and
memory (see [46] for a review). Only few studies have directly
addressed the relation between mindfulness and cognitive flexibility
or rigidity. Although some studies did not find differences between
meditators and non-meditators in rigidity related tasks (e.g [47,48]),
others have found that meditators exhibit decreased Stroop
interference [49,50](in a Zen meditation sample). The Stroop task
requires participants to name the ink color in which color words are
written. The interference reflects automaticity with regards to the
fact that participants cannot avoid reading the words. This inability
to flexibly adapt to novel and non-habitual task requirements may
be taken as evidence for inflexibility. Along the same line, other
studies found that meditators exhibit superior visual perspective
switching on a multiple perspective images task [51], exhibit
superior verbal fluency [52,53], and perform better than controls
on a category production task [54] and the Hayling task, requiring
participants to complete sentences with unrelated and nonsensical
words [53]. Mindfulness meditators have also been shown to
exhibit reduced rumination compared to controls [38–40], which
may also be related to reduced rigidity as reflected in the adoption
of repetitive thought patterns concerning distressing symptoms,
their causes and implications [55].
Importantly, none of the aforementioned tasks tap the tendency
to be ‘‘blinded’’ by experience, and overlook simple, obvious novel
solutions to a given problem, which is what we studied in this
work. To this end, we adopted the water jar paradigm developed
by Luchins [56]. We had chosen this task over other measures of
rigidity since it directly captures the notion of missing obvious
adaptive solutions that lie right ‘‘under the nose’’ due to being
caught up in learned and repetitive thought patterns. Further-
more, this particular form of rigidity seems most relevant to
mindfulness meditation, which is said to involve relating to the
present situation with decreased reliance on former knowledge and
experience [57]. The water jar paradigm was designed to measure
the Einstulling effect, a term used to describe rigid thought patterns
formed through experience which prevents identifying more
adaptive approaches and solutions. In this task, participants are
required to use three hypothetical jars to obtain a specific amount
of water. Initial problems are solvable by the same complex
formula, but in later ‘‘critical’’ problems a much simpler formula is
also appropriate. In these trials, experience is said to comprise
a ‘‘trap’’ which may result in overlooking the simple formula. A
rigidity score is compiled, reflecting the degree of perseverative use
of the complex formula. Since mindfulness is said to be
characterized by focusing on the present moment with a ‘‘begin-
ners’ mind’’, we hypothesize that mindfulness experience would
result in lower rigidity scores. This hypothesis was examined in
two studies. Experiment 1 compared a sample of experienced
mindfulness meditators with a comparison group of people who
had taken an active interest in mindfulness and had registered to
a mindfulness retreat, yet at the time of assessment did not have
any formal meditation experience. We chose this group in an
attempt to match meditators inclinations and personality char-
acteristics. In Experiment 2, we compared two, randomly assigned
groups of non-meditators: a group who underwent eight sessions of
structured mindfulness training and a waiting list group, before
and after mindfulness training of the mindfulness group.
Methods
Experiment 1
Participants. The experienced meditation group was com-
posed of 14 mindfulness (Vipassana, [29]) meditators (7 males,
mean age = 37.29, SD = 8.44), having minimum meditation
experience of three years (M= 8.54 years, SD = 4.39) and
practicing regularly (M= 3.20 hours per week, SD = 2.26). Data
regarding experience were available for all but two experienced
meditators. The control group, from here on referred to as the
Pre-meditation group, was composed of 21 individuals (8 males,
mean age = 31.24, SD = 10.29) with no meditation experience,
who had registered for their first meditation retreat. Participants
were recruited via poster ads and telephone through a mindfulness
meditation (Vipassana) association in Israel. There was no
significant difference between groups in age [t(25) = 0.88, ns] nor
in gender (p= .36, Fisher’s exact test). Self reported Psychometric
Entrance Test (PET) score, the Israeli equivalent of the SAT
scores, served to assess the equivalence of the groups in academic
abilities. PET scores have previously been found to highly
correlate (r = 0.81) with scores on the Wechsler Adult Intelligence
Scale-Revised [58]. A PET equivalent score was calculated for two
participants who had not taken the PET, via a regression model
provided by Oren (Personal communication 6.11.2010) for the
average high school matriculation exam score, based on a sample
of 65,000 students studying in academic institutions, data of which
can be found at the Israeli National Institute for Testing and
Education (NITE). Six participants from the pre-meditators group
and two from the meditators group were unable to report PET or
matriculation exam data. Meditators (M= 656.91, SD = 52.79) did
not significantly differ in their academic abilities as assessed by the
PET score from pre-meditators [M= 689.27, SD = 68.37;
t(23) = 1.34, ns]. All participants were offered a mindfulness
related book as compensation for attendance. The experiment had
received approval from the psychology department’s ethics
committee in Ben-Gurion University.
Measures. Water jar task: A computerized version of the task
was administered using E-Prime (Psychological Software Tools,
Inc.), with problems adapted both from Luchins [56] and Schultz
and Searman [59] (see Table 1). Participants viewed three jars
onscreen marked A, B, and C with numbers indicating their size,
and a target cup indicating the goal to obtain. Participants were
instructed to obtain the goal amount of water by adding or
subtracting the jars given in each problem, while applying the
simplest and shortest solution.
Participants inserted their solution by toggling between the
‘‘add’’ and ‘‘subtract’’ options and typing the number of jars
desired to be added or subtracted in the adjacent textbox beneath
each jar (see Figure 1 for an example translated from Hebrew to
English). Participants were provided with scrap paper and a pen to
assist in calculations. After verifying that participants compre-
hended instructions and mastered onscreen navigation, partici-
pants were given an example question and were encouraged to ask
questions. Once solved correctly, the experimenter left the room
and participants independently solved the presented problems.
The first trials were set trials, solvable by the formula B-A-2C, in
which participants were required to add one B jar, subtract one A
jar, and subtract 2 C jars (e.g. obtaining 100 units of water with
jars the capacity of 21, 127, and 3 units by performing
1272212323 = 100). Once 6 out of the maximum of 10 set
trials were correctly solved, participants were presented with 3
critical trials, solvable both by the complex B-A-2C formula and by
a simple formula: either A+C or A-C (e.g. obtaining 18 units of
water with jars the capacity of 15, 39, and 3 units by performing
15+3 = 18, as opposed to using the more complex formula -
392152323 = 18). Participants were then presented with two
extinction trials, solvable only with the simple formula. Participants
were instructed not to spend more than 5 minutes on each
problem. One rigidity point was given for each critical or
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extinction trial solved using the complex formula, and for each
extinction trial exceeding a cutoff of 60 seconds solving time.
Exclusion from analyses criteria included the use of fractions
rather than whole jar numbers, correctly utilizing the ascribed
complex solution on less than six ‘‘set’’ trials, and performing any
calculation errors or applying alternative novel solutions (which
were evidently possible in a few of the problems) on the two final
‘‘set’’ trials prior to critical trials, as well as on critical trials. These
were assured in order to facilitate and standardize both mental set
formation prior to critical trials, and rigidity score compilation.
Procedure. Participants entered a room containing a com-
puter. They signed an informed consent form, and then carried
out the water jar task. At the end of the experiment participants
had answered a few demographic questions regarding age,
psychometric exam score, and meditation experience. At the end
of the session participants were debriefed.
Experiment 2
Participants. Seventy six individuals with no former medi-
tation experience were recruited via poster ads hung around Ben-
Gurion University campus and email ads sent to all university
students, offering a free mindfulness program for those participat-
ing in two experimental sessions. The program was due to start in
two possible dates several months apart. Exclusion criteria
included people with learning disabilities and non-native Hebrew
speakers, due to the mathematical and lingual nature of the tasks,
as well as people with previous meditation background. Following
the first experimental session, participants were randomly assigned
to a Mindfulness meditation group (N = 38) intended to partake in
the first program and a waiting list (control) group (N = 38)
intended to partake in the second program. No significant
differences were found between groups in Age [M= 25.45,
SD = 2.56 for meditators, M= 26, SD = 2.5 for controls,
t(74) = 0.95, ns], gender (13 male meditators, 15 male controls,
p= .41, Fisher’s exact test), nor in academic abilities as measured
by PET scores [M= 662.97, SD = 62.22 for meditators,
M= 672.66, SD = 57.37 for controls, t(74) = 0.70, ns]. Demo-
graphic characteristics of participants included in baseline analysis
are depicted in Table 2.
Measures. Alphabet-maze: Since the water jar task may lose
much of its efficacy if administered in both experimental sessions
(due to previous exposure to short solutions on extinction trials), it
had been administered only in the second session, after
mindfulness training of the mindfulness group. Initial differences
in Einstellung rigidity between groups had been assessed in the
first experimental session using a task similar in structure to the
water jar task, the Alphabet-Maze task, which is described in detail
by Cowen [60]. A Hebrew version of this task was administered
via a computer using E-Prime software. An array of Hebrew letters
appeared onscreen. Participants were told that the object of the
task is to move from upper-left corner of the maze to the bottom-
right corner, spelling out words as they go along (the original
direction of the English task has been reversed since Hebrew is
written from right to left). Once a word has been spelled,
participants may move in any direction (up, down, right, left or
diagonally) to spell the following word. Words must be at least 3
letters long. As with the water jar task, instructions encouraged
solving rather quickly, yet strongly emphasized that the goal was to
reach the end via the shortest and most direct solution, using as
few letters as possible. After solving two example questions and
verifying comprehension of instructions, participants were pre-
sented with six set trials, solvable by a long solution (a down-right
diagonal movement, followed by a straight down movement, and
finally directly to the right). Once solved, participants had written
on paper the words taking them from start to end, and pressed the
space bar to continue to the following trial. The next four trials
were critical (also named trap or crucial trials), solvable by both the
long solution and a short solution (a straight diagonal path for the
Table 1. Water Jar Problems in Both Studies.
Experiment 1 Experiment 2
Trial Type Jar A Jar B Jar C
Goal to
obtain Jar A Jar B Jar C
Goal to
obtain Shortest Solution
Example 29 3 0 20 29 3 0 20 A-3B
Set 31 61 12 6 31 61 12 6 B-A-2C
Set 22 57 10 15 22 57 10 15 B-A-2C
Set 18 59 16 9 18 59 16 9 B-A-2C
Set 20 67 13 21 20 67 13 21 B-A-2C
Set 22 57 10 15 22 57 10 15 B-A-2C
Set 24 52 3 22 21 127 3 100 B-A-2C
Set 19 42 3 17 18 43 10 5 B-A-2C
Set 21 127 3 100 24 52 3 22 B-A-2C
Set 18 43 10 5 19 42 3 17 B-A-2C
Set 14 163 25 99 14 163 25 99 B-A-2C
Critical 18 48 4 22 18 48 4 22 A+C
Critical 15 39 3 18 15 39 3 18 A+C
Critical 23 49 3 20 23 49 3 20 A2C
Critical – – – – 7 16 2 5 A2C
Extinction 14 39 8 6 14 39 8 6 A2C
Extinction 13 37 5 18 13 37 5 18 A+C
doi:10.1371/journal.pone.0036206.t001
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upper-left to the lower-right corners). Finally, two extinction trials
were presented, solvable only by using the short solution. Rigidity
scoring was identical to that of the water jar task, i.e. one rigidity
point given for each critical or extinction trial solved using the
complex formula, and for each extinction trial exceeding a solving
time of 60 seconds. A few problems were evidently solvable by
more than one solution. Data were considered valid if at least 4 out
of the 6 set trials were solved in the intended method, and no
alternative solutions were applied in critical trials nor in the two
final set trials.
Water jar task: Task was similar to that described in Experiment
1, with a few modifications. Task programming was modified to
prevent the possibility of continuing to the next trial if the current
one was mathematically incorrect, and order of a few set trials was
modified to postpone trials more prone to be given alternative
solutions. Both modifications were applied in order to maximize
mental set constitution and minimize invalid or unscorable data by
preventing the application of mathematically incorrect solutions
and minimizing as much as possible the number of solutions other
than the intended ones. Additionally, number of critical trials was
Figure 1. Illustration of computer display on critical trial (English version). Following instructions to apply the shortest and simplest
solution, participants entered the desired number of jugs of each type in the dialog box at the bottom, and toggled between the ‘‘add’’ and
‘‘subtract’’ options to reach the target amount specified on the right.
doi:10.1371/journal.pone.0036206.g001
Table 2. Demographic characteristics of participants in Experiment 2.
Controls Meditators
Mean SD Min Max Mean SD Min Max
Gender 69% Women 69% Women
Age 25.50 2.74 20 35 26.06 2.63 20 33
Education
Level
88% under-grad Under-grad PhD 88% under-grad Under-grad PhD
PET Score 674.43 57.61 567 783 660.38 654.79 480 763
Rigidity score
at session 1
3.50 2.00 0 6 2.78 2.09 0 6
Data consists of the 32 participants in each group with valid rigidity scores in Session 1.
doi:10.1371/journal.pone.0036206.t002
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increased from 3 to 4 (See Table 1) in order to enhance the
reliability and hence the statistical power.
Mindfulness Program. The mindfulness program was de-
veloped in Be’er-Sheva’s Mental Health Center, based on the
Mindfulness Based Cognitive Therapy program [33] with
adaptations to include handling general stress and everyday
difficulty rather than contents limited to depression. The program
was conducted over a period of six weeks, and consisted of seven 2
hour group sessions, and an additional half day retreat at the end
of the fifth week. During each session the instructor guided the
participants through different meditations including breathing
meditation, body scan, open awareness meditation, walking
meditation and compassion meditation. A detailed description of
the instructions provided for the different meditations is presented
in Table 3. Each session additionally included different awareness
exercises, stories and group discussions to allow a broader
understanding of mindfulness principles, and provide the partic-
ipants with opportunities to share their meditation experiences.
Daily home practice of formal meditation of at least 20 minutes
was required, as well as informal daily mindfulness practice in
which participants attend to regular daily activities in a mindful
manner. Audio CD’s with meditation instructions were provided
to facilitate home practice. Additionally, participants received
a daily email notification directing them to an online diary for
filling a report of their daily home practice. During the half day
retreat participants practiced different formal meditations in
silence, with no exercises or group discussions. The program was
led by one of the authors (KR), a trained mindfulness based
therapy instructor and psychologist, with a personal mindfulness
meditation experience of over ten years. The instructor was blind
to the hypothesis of the experiment.
Procedure. In the beginning of each of the two experimental
sessions, participants signed an informed consent form. In Session
1 they then performed the Alphabet-maze task. Participants were
then randomly assigned to groups. The randomization procedure
involved using the ‘‘random’’ function in Python programming
language to assign half of the participants to each group by
participant number. Session 2 took place near the end of the
mindfulness program. Participants completed a Competitor Rule
Suppression task (CRS) [61], which does not involve Einstellung
rigidity and will not be discussed in the current paper. They then
completed the water jar task.
Results
Experiment 1
Six participants of the Pre-meditation group and two partici-
pants from the experienced meditation group met exclusion
criteria and were excluded from the main analysis. Due to our
directional hypothesis concerning rigidity scores, we had per-
formed one-tailed tests on both studies, although almost all
differences reach a two-tailed significance level. As hypothesized,
experienced mindfulness meditators (M=1.17, SD = 1.75) attained
significantly lower rigidity scores than pre-meditators [M= 2.93,
SD = 2.02; t(25) = 2.40, p= .01, g
2
= 0.19; Post hoc power,
calculated by GPower software [62] = 0.78]. The effect increased
considerably once Age and PET scores had been added as
a Covariates to the analysis in a one way ANOVA [F(1,16) = 9.81,
p,.01, g
2
= 0.38; Post hoc power = 0.96]. Group differences in
rigidity scores remained significant after we had performed the
comparison on all 35 original participants (14 experienced
meditators, 21 pre-meditators), including those who had met the
exclusion from analyses criteria as specified in the Method section,
in order to insure that group differences were not accounted for by
the exclusion criteria [t(33) = 2.42, p= .01, g
2
= 0.15; Post hoc
power = 0.77].
Since there was a certain degree of arbitrariness in determining
the time cutoff for extinction trials in calculating rigidity scores, we
re-calculated rigidity scores using various alternative solving time
cutoffs for extinction trials (60, 90, 120 seconds). The significant
group differences in rigidity scores remained in all t-tests (minimal
t= 2.40, p= .01, g
2
= 0.15; Post hoc power = 0.67).
Experiment 2
Since correlation between rigidity scores of the alphabet-maze
and the water jar task was low and non-significant (r =.10, ns)
results from these tasks are hereby reported separately.
Table 3. Instructions for the various meditations in the mindfulness program.
Instructions Meditation
Participants were asked to sit still with their eyes closed and focus their attention on the sensations of their breath. Whenever they
noticed that their attention wandered off from their breath they were asked to observe the object of their attention
in the present moment, whether it is a thought, an emotion or a sensation, without judgment
or reaction, and then bring their attention gently back to the breath.
Breathing meditation
Participants were asked to sit still with their eyes closed and focus their attention on bodily sensations in different parts of their body,
according to the given instructions. When they noticed that their attention had wandered off from the sensations in the specified
body part they were asked to observe the object of their attention in the present moment without judgment or reaction, and then
bring their attention gently back to the sensation in the specified body part.
Body scan meditation
Participants were asked to sit still with their eyes closed and focus their attention on different qualities of the present moment,
for example, sounds, smells, body sensations and the breath. When they noticed that their attention had wandered off from the
present they were asked to observe the object of their attention without judgment or reaction, and then bring their attention
gently back to the present moment.
Open awareness
meditation
Participants were asked to sit still with their eyes closed and think of someone they care about. Participants were then asked to wish
that this person will be free from suffering, distress or loss, and will experience joy, peace and love. Participants were asked to do
the same for someone they did not know well, for someone with whom they have a conflict, and for themselves.
Compassion meditation
Participants were asked to walk slowly and silently, and notice the different segments and sensations of walking. When they noticed
that their attention had wandered off from walking, they are asked to stand still and notice where their attention is at the
present moment, without judgment or reaction and then bring their attention gently back to the present moment
and resume the walking.
Walking meditation
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Alphabet-maze. Data from six participants of each group
were excluded due to meeting exclusion criteria (see Measures
section). No significant differences were found in initial rigidity
scores between the mindfulness group (M= 2.78, SD = 2.09) and
the waiting list group [M= 3.50, SD = 2.00; t(62) = 1.41, ns; Post
hoc power = 0.40]. This lack of group differences in initial rigidity
scores remained after additionally excluding participants who did
not take part in the second experimental session [t(55) = 1.21, ns;
Post hoc power = 0. 27], and participants who were excluded from
the main analysis of the water-jar task [t(45) = 1.44, ns; Post hoc
power = 0.33]. Thus, groups were statistically equivalent in initial
rigidity scores.
Water-Jar Task. Four participants from each group chose
not to participate in the second experimental session, and are
therefore missing water-jar task data. Water jar data were
excluded from two additional meditators who attended less than
four program meetings. Nine participants (3 meditators) met water
jar exclusion criteria (see Experiment 1). Two additional
participants of each group were excluded from main water-jar
analyses, one who reported being familiar with the task and its
objective, and three others failed to properly comprehend jar
usage instructions. Thus, data on main analyses are reported from
27 meditators and 26 controls.
In accordance with our hypothesis, following the mindfulness
program, the mindfulness group (M= 2.19, SD = 2.09) received
significantly lower rigidity scores than the waiting list group
[M= 3.42, SD = 2.18; t(51) = 2.11, p,.02, g
2
= 0.08; Post hoc
power = 0.67]. This effect slightly increased in a one way ANOVA
in which Age and PET scores were added as Covariates to the
analysis [F(1,49) = 6.28, p,.01, g
2
= 0.11; Post hoc power = 0.81 ].
In the latter analysis, a main effect was found for PET scores, with
higher rigidity scores attributed to those with low PET scores
[F(1,49) = 5.76, p,.05], indicating that academic ability is
negatively related to Einstellung rigidity. Group differences in
rigidity scores remained significant in a similar ANOVA which
included the nine participants who had met the water jar task
exclusion criteria specified in Experiment 1, the participant who
was familiar with the task, and the two participants who
participated in less than four meetings [F(1,61) = 4.24, p=.02,
g
2
= 0.07; Post hoc power = 0.70], verifying that the effect is not
due to exclusion criteria. A series of t-tests comparing groups’
rigidity scores using various cutoff times for extinction trials
(60,90,120 seconds) revealed that group differences remained
significant on all cutoff times (minimal t= 1.88, p= .03, g
2
= 0.07;
Post hoc power = 0.63).
Discussion
Mindfulness meditation has been described as involving
adoption of a ‘‘beginner’s mind’’ and ‘‘being in the present
moment’’ [31]. We therefore hypothesized that mindfulness may
reduce cognitive rigidity and immune one from being ‘‘blinded’’
by past experience, as measured by the Einstellung water jar task.
In Experiment 1, as hypothesized, following repetitive experience
with a complex problem solving method, experienced mindfulness
meditators were less blinded by experience and were better able
than pre-meditators to identify the simple novel solution. In
Experiment 2, similar results were obtained following mindfulness
training in which participants were randomly assigned to
mindfulness training vs. waiting list groups. These findings lend
support to the notion that mindfulness involves cultivation of
a ‘‘beginner’s mind’’, and demonstrate that mindfulness practice
reduces cognitive rigidity via the tendency to overlook simple
novel solutions to a situation due to rigid and repetitive thought
patterns formed through experience.
The present findings coincide with previous findings in which
meditators outperformed non-meditators in tasks such as verbal
fluency [52,53], and visual perspective switching [51], in the
respect of exhibiting an improved ability to generate varied
responses to the same stimuli following mindfulness practice.
Findings of the current study also coincide with previous findings
indicating that meditators may exhibit decreased interference in
the Stroop [49,50] and Hayling [53] tasks in the sense of decreased
automatic and habitual responding following mindfulness practice.
Our findings additionally converge with findings regarding
decreased rumination [38–40] in the sense of a reduction in
repetitive and perseverative negative thoughts (see [63] for
a discussion regarding such repetitive thinking). Findings of the
current study bear novel contributions to the existing literature
firstly by demonstrating that reductions in such rigid repetitive
thinking patterns following mindfulness practice are evident
regardless of thought valence or specific content and therefore
reflect reduction in cognitive rigidity rather than a specific
reduction in rigid ruminative content. Note that the measures of
verbal fluency, visual perspective switching, Stroop, and Hayling
tasks mentioned above, measure the ability to overcome over-
learned habits rather than repetitive thinking patterns which have
just been formed as does the Water jar task. An additional and
central novel contribution of this study regards the increased
ability to identify and utilize simple novel yet obvious solutions
despite having experienced a successful, albeit complex approach
in the recent past. Interestingly, the benefit of mindfulness was not
restricted to years of experience and was found even following
a six-week intervention.
Individuals suffering from depression and particularly those at
suicidal risk tend to exhibit a narrowing of perceived options and
difficulty in considering alternatives, a tendency which may prove
fatal [64]. A similar narrowing of thought and difficulty in
considering alternatives often occurs in instances of alcohol use
and abuse. This phenomenon has been termed ‘‘alcohol myopia’’,
and has been found to facilitate extreme social responses [65,66].
Although in need of future examination, it is tentatively suggested
in light of the current results that reductions in such ‘‘blindness’’ to
alternatives due to rigid thought patterns may (partly) underlie the
efficacy of mindfulness in treatment of the above conditions
[34,41].
Additional implications of the current findings may regard other
common situations, clinical as well as non-clinical, in which
individuals may be rigidly ‘‘blind’’ to adaptive solutions or
alternative courses of action due to previous experience. As
illustrated in the beginning of this paper, overlooking the correct
clinical diagnosis often occurs in cases that seem familiar but do
not actually match clinicians’ past experience [1]. Mental health
professionals often have difficulty in offering new perspectives and
reframing the situation after having repeatedly heard their clients’
impressions [2,3], and that managers and decision makers in
organizations often experience trouble replacing existing proce-
dures with more adaptive ones [4]. Findings of the current study
suggest that mindfulness training may be useful in these and
similar cases.
A number of methodological limitations should be considered
regarding the present studies. Sample size, particularly in
Experiment 1, was relatively small, due to the difficulty in
reaching and recruiting the relevant populations. In Experiment
2, we compared a mindfulness intervention group with a waiting
list group. This comparison enables the examination of the
effects of a mindfulness intervention program as a whole rather
Mindfulness Reduces Cognitive Rigidity
PLoS ONE | www.plosone.org 6 May 2012 | Volume 7 | Issue 5 | e36206
than the effects of specific components within the intervention
such as experiencing intervention. A third limitation concerns the
water jar task. One of the main merits of this task is its
examination of the tendency to overlook novel yet obvious
solutions due to experience. This merit, however, also encom-
passes a shortcoming of the task, which is the fact that it may
only be efficiently administered once. While this prevented
examination of performance on the same task pre and post
intervention, the equivalent performance on a task similar in
structure at baseline level and the random assignment to groups
practically resolves this shortcoming.
Future research may examine rigidity related effects that are
specific to mindfulness interventions. This may be done by
comparing mindfulness with active control groups and other
intervention programs. A second direction for future research
involves investigating the relationship between the effects of
mindfulness training on the Einstellung effect and salient clinical
outcomes in various forms of psychopathology. This may both
extend the validity of the water jar task, a rigidity measure
previously examined primarily in healthy individuals [6], to
include rigidity in psychopathology, and may allow making more
clearly established clinical implications than could have reached in
the current study.
Author Contributions
Conceived and designed the experiments: JG KR NM. Performed the
experiments: JG KR. Analyzed the data: JG NM. Contributed reagents/
materials/analysis tools: JG KR NM. Wrote the paper: JG KR NM.
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