The role of (dis)inhibition in creativity: Decreased inhibition improves idea generation

Abstract

There is now a large body of evidence showing that many different conditions related to impaired fronto-executive functioning are associated with the enhancement of some types of creativity. In this paper, we pursue the possibility that the central mechanism associated with this effect might be a reduced capacity to exert inhibition. We tested this hypothesis by exhausting the inhibition efficiency through prolonged and intensive practice of either the Simon or the Eriksen Flanker task. Performance on another inhibition task indicated that only the cognitive resources for inhibition of participants facing high inhibition demands were impaired. Subsequent creativity tests revealed that exposure to high inhibition demands led to enhanced fluency in a divergent thinking task (Alternate Uses Task), but no such changes occurred in a convergent task (Remote Associate Task; studies 1a and 1b). The same manipulation also led to a hyper-priming effect for weakly related primes in a Lexical Decision Task (Study 2). Together, these findings suggest that inhibition selectively affects some types of creative processes and that, when resources for inhibition are lacking, the frequency and the originality of ideas was facilitated.

Full text

The role of (dis)inhibition in creativity: Decreased inhibition
improves idea generation
Rémi Radel
a,
⇑
,1
, Karen Davranche
b
, Marion Fournier
a
, Arne Dietrich
c
a
Laboratoire LAMHESS (EA6309), Université de Nice Sophia-Antipolis, France
b
CNRS, Université d’Aix-Marseille, France
c
American University of Beirut, Lebanon
article info
Article history:
Received 8 July 2013
Revised 26 August 2014
Accepted 11 September 2014
Available online 17 October 2014
Keywords:
Creativity
Inhibition
Cognitive control
Hypofrontality
Semantic priming
abstract
There is now a large body of evidence showing that many different conditions related to
impaired fronto-executive functioning are associated with the enhancement of some types
of creativity. In this paper, we pursue the possibility that the central mechanism associated
with this effect might be a reduced capacity to exert inhibition. We tested this hypothesis
by exhausting the inhibition efficiency through prolonged and intensive practice of either
the Simon or the Eriksen Flanker task. Performance on another inhibition task indicated
that only the cognitive resources for inhibition of participants facing high inhibition
demands were impaired. Subsequent creativity tests revealed that exposure to high inhibi-
tion demands led to enhanced fluency in a divergent thinking task (Alternate Uses Task),
but no such changes occurred in a convergent task (Remote Associate Task; studies 1a
and 1b). The same manipulation also led to a hyper-priming effect for weakly related
primes in a Lexical Decision Task (Study 2). Together, these findings suggest that inhibition
selectively affects some types of creative processes and that, when resources for inhibition
are lacking, the frequency and the originality of ideas was facilitated.
Ó2014 Elsevier B.V. All rights reserved.
1. Introduction
The ability most frequently said to reflect human
uniqueness is creativity. Human beings are able to create
and this ability is expressed in a variety of different
domains such as art, technology, or science. At the same
time, our uniqueness is also characterized by higher cogni-
tive functions which have emerged with the growth of the
human prefrontal cortex (PFC) (Deacon, 1997; Ruff,
Trinkaus, & Holliday, 1997). These executive functions
are composed of three main components: mental-set
shifting, inhibitory control, and updating working memory
(Miyake et al., 2000).
From this, one might infer that creativity comes from
our ability for executive functioning. However, one of the
most intriguing finding in psychology and psychiatry is
that many kinds of mental states that are associated with
impaired executive functioning can lead to positive conse-
quences in terms of creative performance (Dietrich, 2004).
For example, White and Shah (2006) showed that ADHD
individuals outperformed non-ADHD individuals on a
divergent creativity task which requires participants to
find multiple ideas. Interestingly, Healey and Rucklidge
(2006) noted that 40% of highly creative children met crite-
ria for ADHD. Keri (2009) indicated that a specific gene (i.e.,
neuregulin 1; T/T), which has been previously associated
with fronto-executive disfunctioning and schizophrenia
(Hall et al., 2006), is positively associated with real-life
http://dx.doi.org/10.1016/j.cognition.2014.09.001
0010-0277/Ó2014 Elsevier B.V. All rights reserved.
⇑
Corresponding author at: 261, route de Grenoble, 06205 Nice cédex 3,
France.
E-mail address: remi.radel@gmail.com (R. Radel).
1
This work was supported by the French research agency (ANR; grant
number: ANR-13-JSH2-0007).
Cognition 134 (2015) 110–120
Contents lists available at ScienceDirect
Cognition
journal homepage: www.elsevier.com/locate/COGNIT

creative achievements. In a neurological study, Reverberi,
Toraldo, D’Agostini, and Skrap (2005) showed that patients
with lateral frontal lesions were better than normal partic-
ipants at solving hard insight problems. Similarly, a recent
study showed that a decrease in cortical excitability of the
lateral frontal cortex, induced by transcranial magnetic
stimulation, improved performance on a divergent creativ-
ity task (Chrysikou et al., 2013). A psycho-pharmacological
study by Morgan, Rothwell, Atkinson, Mason, and Curran
(2010) showed that cannabis intoxication elicited a hyper
semantic priming effect. Under marijuana, the perception
of a stimulus generated the activation of a greater network
of distantly related concepts, which is considered an
important aspect of creativity (Martindale, 1995). Also,
enhanced problem solving was found when individuals
worked at a non optimal time of the day compared to an
optimal time of the day (Wieth & Zachs, 2011). This raises
the question of why all these different conditions lead to the
same positive effect. In the present research, we propose
that they might all in fact be linked to the same process.
That is, we donot assumethat a reduced executive function-
ing in general is at work but rather a reduced capacity to
exert inhibition. Indeed, it is known that the capacity to
exert the inhibition function is impaired by cannabis use
(Skosnik, Spatz-Glenn, & Park, 2001) and tends to be affected
by the circadian rhythm (May, 1999). Impaired inhibition is
also a suspected symptom in ADHD (Barkley, 1997)and
schizophrenia patients (Beech, Powell, McWilliam, &
Claridge, 1989). In addition, dysfunction of the lateral frontal
cortex is typically related to reduced inhibition as this func-
tion is mainly located in this region, especially the inferior
frontal cortex (e.g., Aron, Robbins, & Poldrack, 2004). Given
that impaired inhibition is the common denominator of all
these various conditions, we suggest that this dysfunction
can have a paradoxical effect, favoring some types of creativ-
ity while being detrimental to others.
1.1. Inhibitory control
The function of inhibition, also called inhibitory control,
is the ability to suppress the processing or expression of
information that would disrupt the efficient completion
of the goal at hand (Dempster, 1992). As such, inhibition
provides a resistance to interference from irrelevant action.
Inhibition also plays a key role in cognitive processing by
limiting the content of consciousness to goal-relevant
information. In other words, inhibition is thought to be
the mechanisms behind selective attention, narrowing
the focus of attention around one limited source of infor-
mation (Hasher, Lustig, & Zacks, 2007). When inhibitory
control is inefficient, a broader range of information will
penetrate working memory causing the apparition of less
relevant thoughts (e.g., May & Hasher, 1998).
Response inhibition can be assessed using well-known
tasks such as the Eriksen and Eriksen (1974), Simon
(1990),orStroop (1935) tasks. In such conflict tasks, par-
ticipants are required to respond, as quickly and accurately
as possible, by selecting the relevant feature of the stimu-
lus and inhibiting the irrelevant feature which is associated
with the incorrect response. Reaction time (RT) and accu-
racy performances are usually reported to be worse when
relevant and irrelevant information are mapped to differ-
ent responses (incongruent trials, IN), than when they cor-
respond to the same response (congruent trials, CO). This
phenomenon is known as the interference effect (RT on
incongruent trials minus RT on congruent trials) and is
interpreted as resulting from a conflict between alternative
responses. The conflict paradigm provides reliable indica-
tor of the cognitive control efficiency (see van den
Wildenberg et al., 2010).
1.2. Types of creativity
Creativity can be described as the production of an
innovative, appropriate, and surprising solution to a com-
plex problem. In spite of this simple definition, creativity
is a complex concept with many different processes
involved (Dietrich, 2007; Ward, Smith, & Finke, 1999).
Recent models (Allen & Thomas, 2011; Dietrich, 2004;
Helie & Sun, 2010) indicate that while some of these pro-
cesses require heavy executive processing (e.g., learning
the context of the problem, analytic strategy of search,
checking the correctness of a solution), others would rather
rely on automatic associative processing (e.g., imagination,
generation of ideas). Depending on the type of creative task,
not all of these aspects are equally important. For example,
while aspects requiring executive processing could be quite
important in convergent creativity tasks, it might be not so
important in divergent creativity tasks. Divergent creativity
refers to the generation of multiple ideas or solutions to a
problem. Convergent creativity requires finding a unique
solution to a closed ended problem. Divergent thinking is
typically assessed using the Alternate Use Task (AUT,
Guilford, 1967) that requires finding alternative uses for
an object. As for convergent creativity, the Remote Associate
Task (RAT, Mednick, 1962) is the most frequently used task.
This task consists of numerous problems that require find-
ing one unique word that can be associated to three other
words. Given that many criteria must be met for a conver-
gent creativity problem, it should require more executive
processing. Inhibitory control would be specifically needed
to prevent all irrelevant ideas (e.g., words that are semanti-
cally related to only one or two of the words of a RAT prob-
lem) to enter working memory. The resolution of these
interferences may be crucial to stay focused on identifying
a solution that meets all criteria. However, selective atten-
tion would not be as useful if the goal is to come up with
many ideas. If the task does not require many constraints,
the apparition of a broad range of unfiltered information
in working memory might in fact be an advantage to gener-
ating a number of original ideas.
1.3. The present research
The present study aims to examine how inhibition con-
tributes to creativity. While Carson, Peterson, and DM
(2003) suggested that low inhibition is associated with
high levels of creativity, we assume that low inhibition
would not favor creativity as a whole but rather serves
the more specific process of idea generation. In addition,
unlike previous work on the role of inhibition in creativity
(Carson et al., 2003; White & Shah, 2006), the present
R. Radel et al. / Cognition 134 (2015) 110–120 111

research aims to selectively manipulate inhibition to pro-
vide a direct test of this hypothesis. For example, if the
reduced ability for inhibition of ADHD patients is used to
explain better divergent thinking skills (White & Shah,
2006), it is not possible to make firm conclusions about
the role of inhibition in creativity because ADHD is also
associated with several other cognitive dysfunctions (e.g.,
impulsivity, hyperactivity, mood disorder, see Wilens &
Spencer, 2010).
In our study, the cognitive resources to exert inhibition
was directly manipulated through prolonged exposure on
a conflict task. Inhibition, like all other executive functions,
requires limited and easily depleted resources (e.g.,
Schmeichel, 2007). Thus, when an executive function is
continuously engaged, it cannot be maintained for a long
time. Evidence for this limitation of resources is plenty.
For example, the meta-analysis by Hagger, Wood, Stiff,
and Chatzisarantis (2010) on 83 studies indicates that
when participants engage self-control in a first task (a
function that mainly requires inhibitory control), they have
a reduced ability to exert self-control in a second task.
Focusing more directly on inhibition, Persson, Welsh,
Jonides, and Reuter-Lorenz (2007) randomly assigned their
participants to do either a high versus low interference
task for 20 min. The authors showed that intensive practice
reduced the ability to resolve interference on a second task
if the first task placed high demands on interference reso-
lution. Interestingly, tasks that do not require inhibition
but other executive processes were unaffected. In order
to exclusively manipulate the cognitive resources for inhi-
bition, the present study adopted a similar protocol. A high
and low interference version of a conflict task (the Simon
task in Study 1a as well as Study 2 and the Eriksen task
in Study 1b) was set up by manipulating the proportion
of IN trials (50% vs. 10% in Study 1a and Study 2 or 50%
vs. 0% in Study 1b). We chose to adopt a within-subject
design in order to control for individual differences in the
capacity to exert the inhibition function. Another conflict
task (the Eriksen task in Study 1a as well as Study 2 and
the Simon task in Study 1b) was performed before the
manipulation to obtain a baseline value and another time
after the manipulation in order to estimate the alteration
of the inhibition capacity induced by the extended expo-
sure to the conflict task serving for the manipulation.
To test whether low inhibition would have a selective
effect on only the generation of ideas and not creativity
in general, we used both the AUT and the RAT in both ver-
sions of Study 1. We predicted that participants’ perfor-
mance would be affected by the manipulation in the AUT
but not in the RAT. Specifically, participants should, first,
generate more responses, and, second, the originality of
these responses should be higher after the exposure to
the high-demand as opposed to the low inhibition task.
In Study 2, we pursued the same question by measuring
the automatic spreading of activation in a primed Lexical
Decision Task (LDT) in order to better understand how
inhibition affects the generation of original ideas. One of
the main theoretical models assumes that the ability to
generate original ideas is linked to the associative strength
distributions of responses (Mednick, 1962). According to
this view, individuals with a steep gradient (i.e., only the
most typical associations are provided in response to a
stimulus) would be less able to provide original ideas than
individuals with a flat associative response gradient (i.e.,
distant associative concepts are also likely to be used in
response of a stimulus). In the primed LDT task, partici-
pants had to respond to a target after being exposed to a
prime that was closely related, distantly related, or unre-
lated to the target. We predicted that distant primes would
elicit a greater facilitation of the response after facing high
inhibition demands than after facing low inhibition
demands. In other words, we propose that disinhibition
may improve the automatic spreading of activation (for a
similar account see Manschreck et al., 1988).
2. Study 1a
2.1. Participants
The participants were 25 native French speaking volun-
teer adults in Study 1 (Mage = 28.7, SD = 7.4 years) who
were recruited in exchange of course credits. The study
was based on a double-blind, randomized, counterbalanced,
crossover experimental design. Treatment order was ran-
domly allocated according to balanced permutations pro-
vided by an online application (www.randomization.com).
2.2. Procedure
Participants completed three sessions. The interval
between each session was between 1 and 10 days. The first
session was only devoted to familiarization. All tasks were
presented on a computer using E-prime (PST, Pittsburgh,
USA). In a first time, participants were trained on the Erik-
sen Flanker task. Each participant did the task at least four
times. If participants’ responses were stable (accuracy and
RT below 5% of variation with the last task) and sufficiently
fast (average RT below 700 ms) and accurate (above 80% of
correct responses) the training stopped. Otherwise, partic-
ipants were asked to do the task again until these criteria
were met. Then, the participants learnt the Simon task
using one unique block of 100 trials (included 30% of IN tri-
als) and learnt the RAT and the AUT. For all of these tasks,
no specific criteria were set and the experimenter only
ensured that the instructions were well understood.
The two experimental sessions were scheduled on dif-
ferent days but at the same time of the day. The order of
these two sessions was counterbalanced across partici-
pants. The two sessions were identical with the exception
of the manipulation of the degree of inhibition required in
the Simon task. Each session started with a first Eriksen
task to evaluate baseline inhibition performance. Then,
participants performed continuously the Simon task. The
second Eriksen task was done immediately after the com-
pletion of the Simon task. The participants ended the ses-
sion by completing the creativity tests (RAT and AUT) in
a counterbalanced order.
2.3. Manipulation
Two versions of the Simon task were used to manipu-
late participants’ the cognitive resources for inhibition.
112 R. Radel et al. / Cognition 134 (2015) 110–120

After a fixation cross at the center of the screen, a green or
red circle appeared either on the left or on the right side of
the screen until the participants responded. Participants
were asked to respond as fast as possible by pressing a left
or right key of the keyboard with the left or right index
according to the color of the stimulus. In CO trials, the spa-
tial location of the stimulus and response corresponded
(e.g., left stimulus/left response). In IN trials, the spatial
location of the stimulus and response were opposed (e.g.,
left stimulus/right response). In IN trials, the spatial loca-
tion triggered an automatic response that had to be inhib-
ited. In the high inhibition version of the task, 50% of the
trials were IN. Only 10% of IN trials were in the low inhibi-
tion version of the task. The task included a total of 2000
trials.
2.4. Measures
2.4.1. Inhibition
To assess the impact of the manipulation, a modified
version of the Eriksen task was used to measure inhibition
performance before and after the extended completion of
the Simon task. Participants were required to press the
arrow keys of the keyboard, with the left or right index,
according to the direction the center arrow pointed to.
Flanking arrows were either in the same direction for half
of the trials (CO trials) or in the opposite direction for the
other half (IN trials). The complexity of the peripheral sen-
sory processes involved in early sensory operations was
increased by randomly presenting the stimulus at the
upper or the lower side of the screen.
2.4.2. Divergent creativity
The AUT required participants to generate as many uses
as possible for three common household objects. They were
given 2 min per word to write down as many ideas as they
could. Two lists of objects were used for each experimental
session (list 1: bucket, shoe, newspaper; list 2: brick, can,
paperclip). The order of the list was counterbalanced across
participants. For the practice session, participants had to
list as many uses as possible for a pen and a hat. According
to Guilford (1967), scoring comprised four components.
The fluency score reflected the total number of alternative
uses found per object. The originality referred to the
uniqueness of each response and was measured by compar-
ing each response to the total amount of responses given by
all participants. In order to have a larger dataset to assess
creativity, we grouped responses obtained in Study 1a
and Study 1b together. Responses that were given by only
5% of the participants were unusual (1 point), and
responses that were given by only 1% of the participants
were unique (2 points). The points for each object were
then summed and divided by the number of uses given.
The score of flexibility reflected the number of different cat-
egories used per oblect. Finally, the score of elaboration
represented the mean amount of details (from 0 to 2 points
for each response) per object. The points for each object
were then summed. Two coders were used to perform the
scoring in order to attenuate subjectivity biases. The
inter-rater reliability was satisfactory (Krippendorff’s
alphas were as follow: 1 for fluency, 1 for originality,
0.812 for flexibility, and 0.834 for elaboration).
2.4.3. Convergent creativity
The task consisted of a French adaptation (Radel, 2012)
of the RAT that included a list of 20 problems. Participants
were given 6 min for the entire test. They were asked to
type their responses in a window on the screen using the
keyboard. Two lists of different problems were used in a
counterbalanced order. Ten other problems were also used
for the practice session. Rate of correct responses was used
to reflect convergent creativity.
2.5. Results
First, we checked whether the manipulation was effec-
tive by examining the evolution of the inhibition perfor-
mance in the low and high inhibition condition. The
analysis of RT in the Eriksen task was performed after
removing errors, and responses that were too short (below
200 ms) and too long (above 1500 ms). A total of 6.1% of
the responses were removed. The General Linear Model
(GLM) for repeated measures on RT indicated a main effect
of compatibility with faster RT for CO trials than for IN tri-
als, F(1, 24) = 71.372, p< .001,
g
2
= 0.748 (Table 1). In addi-
tion, the interaction effect between the time of
measurement and the condition was significant, F(1,
24) = 5.277, p= .031,
g
2
= 0.180. Only in the condition
requiring high levels of inhibition, the RT tended to
increase after the manipulation, F(1, 24) = 3.176, p= .087,
g
2
= 0.117. Concerning accuracy, a main effect of compati-
bility was also observed with more errors for IN than for
CO trials, F(1, 24) = 82.363, p< .001,
g
2
= 0.774. There was
a main effect of the time of measurement with more errors
made after than before the Simon task, F(1, 24) = 17.035,
p= .001,
g
2
= 0.415. The interaction between the inhibition
condition, compatibility and time of measurement was
also significant, F(1, 24) = 6.646, p= .017,
g
2
= 0.217. For
IN trials, there was a drop in accuracy but only for the task
requiring a high level of inhibition, F(1, 24) = 8.657,
p= .007,
g
2
= 0.265. All other effects did not reach signifi-
cance. In sum, those results indicated that an extended
exposure to a task requiring a high level of inhibition led
to a decreased ability to inhibit irrelevant information.
Mean comparisons for dependent measures were car-
ried out to determine the impact of the manipulation on
the creativity tests (Table 2). Concerning the AUT, signifi-
cant effects were found on the fluency and originality
scores. When exposed to the task with high inhibition
demands participants had a higher fluency and originality
scores than when exposed to the task with the low inhibi-
tion demands, t(24) = 2.529, p= .018, Cohen’s d= 0.527 and
t(24) = 2.216, p= .036, Cohen’s d= 0.447, respectively.
However, no effect was found on flexibility and elabora-
tion, t(24) = 1.433, p= .165 and t(24) = 0.737, p= .468,
respectively. Concerning the RAT, no differences were
observed between sessions, t(24) = .406, p= .689. In
sum, the manipulation only had some effect on some
specific aspects of creativity, principally the generation of
ideational combinations.
R. Radel et al. / Cognition 134 (2015) 110–120 113

3. Study 1b
The aim of Study 1b was to verify if the results of
Study 1a could be replicated in order to provide addi-
tional evidence for the test of the hypothesis that dimin-
ished resources for inhibition would facilitate the
generation of ideas. Given that our version of the Eriksen
task typically provides a greater interference effect than
the Simon task, we decided to switch the role of the
two tasks, in order to have a stronger manipulation of
the cognitive resources needed for inhibition. We also
decided to set a fixed amount of time for the manipula-
tion instead of a fixed amount of trials in order to equal-
ize the time spent by the participants in the conflict task
in each experimental condition. In order to control the
equivalence of the two conditions outside the manipula-
tion of the inhibition function, we measured the per-
ceived fatigue and the motivation of the participants
throughout the task.
3.1. Participants
The participants were 22 native French speaking under-
graduate students (Mage = 20.2, SD = 1.8 years) who were
recruited in exchange of course credits. The study was
based on a double-blind, randomized, counterbalanced,
crossover experimental design.
3.2. Procedure
The procedure of Study 1b was similar to the one used
on in Study 1b. The two studies only differed in the follow-
ing aspects. First, in the familiarization session, the partic-
ipant did the Simon task at least four times (using the same
learning criteria as in Study 1a) but did only one block of
100 trials (included 25% of IN trials) of the Eriksen task.
Second, during the experimental sessions, participants
started with a first session of the Simon task and then
performed the Eriksen task. The second session of the
Table 1
Reaction time (RT) in millisecond and percentage of accuracy during the first and the second session of the conflict task as a function of the inhibition demands
in the other conflict task serving as the manipulation.
Response time (ms) Accuracy (%)
Compatible Incompatible Compatible Incompatible
M (SD) M (SD) M (SD) M (SD)
Study 1a (Eriksen task)
High inhibition demands
First session 452 (36) 497 (49) 96.0 (4.8) 78.3 (12.9)
Second session 456 (35) 514 (53) 94.7 (6.7) 69.7 (19.1)
Low inhibition demands
First session 457 (37) 508 (42) 96.7 (5.3) 75.7 (15.2)
Second session 450 (41) 507 (53) 92.3 (8.3) 74.0 (10.0)
Study 1b (Simon task)
High inhibition demands
First session 425 (47) 435 (43) 95.4 (4.2) 92.7 (9.5)
Second session 435 (34) 445 (37) 92.0 (10.9) 90.5 (7.3)
Low inhibition demands
First session 428 (39) 441 (39) 95.0 (4.3) 93.1 (6.5)
Second session 426 (37) 436 (42) 95.9 (5.0) 94.7 (5.0)
Study 2 (Eriksen task)
High inhibition demands
First session 495 (37) 455 (49) 96.4 (5.0) 79.4 (13.3)
Second session 512 (38) 456 (53) 93.7 (6.9) 71.0 (18.7)
Low inhibition demands
First session 460 (40) 508 (46) 96.4 (5.6) 76.2 (16.3)
Second session 454 (42) 503 (56) 91.7 (8.3) 75.4 (10.0)
Table 2
Mean and standard deviation for creativity scores as function of the inhibition demands in Studies 1a and 1b.
Alternative use task RAT
Fluency Flexibility Originality Elaboration Solving rate
Study 1a
High inhibition demands 6.23 (1.66) 4.80 (1.65) 0.26 (0.15) 0.94 (0.48) 0.38 (0.18)
Low inhibition demands 5.48 (2.06) 4.47 (1.37) 0.21 (0.13) 0.99 (0.46) 0.36 (0.18)
Study 1b
High inhibition demands 5.42 (2.47) 4.05 (1.72) 0.21 (0.19) 0.83 (0.59) 0.36 (0.15)
Low inhibition demands 4.50 (1.37) 3.32 (0.98) 0.20 (0.19) 1.07 (0.80) 0.37 (0.22)
Notes: Standard deviations are displayed in brackets. RAT = Remote Associate Task.
114 R. Radel et al. / Cognition 134 (2015) 110–120

Simon task was done immediately thereafter. Creativity
measurements were administered at the end, as was the
case in Study 1a.
3.3. Manipulation
Two versions of the Eriksen task were used to manipu-
late participants’ resources for inhibition. In the high inhi-
bition version of the task, 50% of the trials were IN. The low
inhibition version of the task included only CO trials. The
task was performed for 40 min. Every 400 s, the partici-
pants had to rate their perceived fatigue and their motiva-
tion to pursue the task on a computerized visual analog
scale (from 0 to 100).
3.4. Measures
3.4.1. Inhibition
The Simon task served to assess the effect of the manip-
ulation on inhibition performance.
3.4.2. Divergent creativity
As in Study 1a, the AUT was used to measure divergent
creativity. The inter-rater reliability was satisfactory (Krip-
pendorff’s alphas were as follows: 1 for fluency, 1 for orig-
inality, 0.840 for flexibility, and 0.827 for elaboration).
3.4.3. Convergent creativity
The RAT was used to measure convergent creativity.
3.5. Results
First, we checked whether the manipulation affected
the level of perceived fatigue and motivation reported by
the participants. Concerning the level of perceived fatigue,
a GLM including the time of measurement and the condi-
tion as within-subjects factors provided a significant linear
effect of the time of measurement [F(5, 17) = 13.068,
p= .001,
g
2
= 0.794], with an increase of perceived fatigue
over time (M= 39, SD = 13 and M= 67, SD = 19), at the first
time and last time of measurement, respectively). No other
effect was found. In addition, the perceived fatigue at the
end of the task did not differ depending on the condition,
t(21) = .958, p= .349. Concerning motivation, a significant
linear effect of the time of measurement was found [F(5,
17) = 9.409, p= .001,
g
2
= 0.735] with a decrease of motiva-
tion over time (M= 53, SD = 15 and M= 30, SD = 15, at the
first time and last time of measurement, respectively). No
other significant effect was found. In addition, the level
of motivation of the participants at the end of the task
did not differ depending on the condition, t(21) = .634,
p= .533. These results suggest the level of inhibition
required by the task did not affect perceived fatigue and
motivation.
Then, we checked whether the manipulation was effec-
tive to affect the cognitive resources devoted to inhibition.
Due to a mistake in entering the session number in the
program running the Simon task, the data of one partici-
pant were lost. The analysis of RT in the Simon task was
performed after removing errors, the responses that were
too short (below 200 ms) and too long (above 1500 ms).
A total of 6.4% of the responses were removed. The GLM
indicated a significant effect of the compatibility with fas-
ter RT for CO than for IN trials, F(1, 20) = 16.052, p= .001,
g
2
= 0.445. An interaction effect between the time of mea-
surement and the condition was also found, F(1,
20) = 4.524, p= .046,
g
2
= 0.184. While there was a signifi-
cant increase in RT after the task requiring a high level of
inhibition [F(1, 20) = 5.196, p= .034,
g
2
= 0.206], there
was no significant change in RT following the task requir-
ing a low level of inhibition. Concerning accuracy, a main
effect was found for compatibility with more errors for
IN than for CO trials, F(1, 20) = 5.834, p= .031,
g
2
= 0.212.
An interaction effect between the time of measurement
and the condition was also found, F(1, 20) = 11.682,
p= .003,
g
2
= 0.369. While there was a decrease of accuracy
after the task requiring a high level of inhibition [F(1,
20) = 12.283, p= .002,
g
2
= 0.380], there was no significant
change in RT following the task requiring a low level of
inhibition. In sum, those results indicated that an extended
exposure to a task requiring a high level of inhibition led to
a general decreased in cognitive performance.
Mean comparisons for dependent measures were car-
ried out to determine the impact of the manipulation on
the creativity tests (Table 2). Concerning the AUT, signifi-
cant effects were found on the fluency and flexibility
scores. When exposed to the task with high inhibition
demands participants had a higher fluency and flexibility
scores than when exposed to the task with the low inhibi-
tion demands, t(21) = 2.289, p= .033, Cohen’s d= 0.575 and
t(21) = 2.107, p= .047, Cohen’s d= 0.486, respectively.
However, no effect was found on elaboration and original-
ity, t(21) = 1.616, p= .121 and t(21) = 0.364, p= .719,
respectively. Concerning the RAT, no differences were
observed between sessions, t(21) = .434, p= .668. These
results closely match with those of Study 1a, as the manip-
ulation of the resources for inhibition only impacted diver-
gent creativity and not convergent creativity. However, if
fluency was significantly improved in both studies follow-
ing the manipulation of the resources for inhibition, the
numerical difference on the originality score did not reach
significance in Study 1b as it did in Study 1a. But the non-
significant numerical difference on flexibility in Study 1a
turned out to be significant in Study 1b. In sum, the deple-
tion of the cognitive resources needed for inhibition only
had some effect on some specific aspects of creativity, prin-
cipally the generation of ideational combinations, and
might also affect the originality and flexibility of the
responses to a lesser extent.
4. Study 2
The objective of Study 2 was to examine why a subop-
timal inhibition performance can improve the generation
of ideas. Many theoretical models relate the ability of gen-
erating ideas to the strength of semantic processing
(Abraham, 2014; Martindale, 1995; Mednick, 1962). For
example, Mednick indicated that individuals who focus
on strong semantic associations would be less able to pro-
vide new ideas than individuals who consider more distant
semantic association in reaction to a stimulus. This
R. Radel et al. / Cognition 134 (2015) 110–120 115

hypothesis has been verified in several studies (e.g.,
Friedman, Fishback, Förster, & Werth, 2003; Manschreck
et al., 1988). For this reason, we wanted to explore if the
inhibition function could in fact have an effect on the
strength of semantic activation. A principal aspect of the
inhibition function is to avoid irrelevant information to
penetrate into the working memory. As such, if inhibitory
processes do not function optimally, more distant informa-
tion may enter working memory (Hasher et al., 2007). If
this function is adaptive in most cases as it allows individ-
uals to focus on the most relevant information, it can also
prevent them to envision different ideas to face a creative
problem. To measure the presence of distant information
in working memory, we used the primed LDT task, in
which participants had to respond to a target after being
exposed to a prime that was closely related, distantly
related, or unrelated to the target. If the reduction of the
capacity to exert inhibition affects the strength of semantic
activation, then distant primes should elicit a greater facil-
itation of the response following high inhibition demands
than following low inhibition demands.
4.1. Participants
The participants were 21 native French speaking stu-
dents (Mage = 21.3, SD = 1.5 years) who were recruited in
exchange of course credits. The experiment was based on
a double-blind, randomized, counterbalanced, crossover
experimental design.
4.2. Procedure
Most of the procedure was similar to the one used in
Study 1a with the exception of the dependent measures.
For this reason, participants ended the first session by
learning the primed LDT. No specific criteria were set for
the learning phase and the experimenter only ensured that
the instructions were well understood for this task.
Concerning the two experimental sessions, participants
did the primed LDT after the second session of the Eriksen
task (see Fig. 1).
4.3. Manipulation
The manipulation of the cognitive resources for inhibi-
tion was the same as in Study 1a.
4.4. Measures
4.4.1. Inhibition
The Eriksen task was used to measure inhibition perfor-
mance in the same way as in Study 1a.
4.4.2. Associative strength
The primed LDT required participants to decide as fast
as possible whether a string of letters was a real French
word or a pseudo-word using one of two labeled keys on
a keyboard. Each trial started with a fixation cross for
200 ms. The prime was presented for 200 ms and followed
by a 200 ms blank screen. Then, the target appeared and
lasted until the participants responded. The inter-trial
interval was 500 ms. The task was composed by 400 trials
with 200 real words and 200 pseudo-words as targets. Tri-
als with real word targets were arranged in three condi-
tions depending on semantic relatedness to the prime:
directly related (40 trials), indirectly related (40 trials),
and unrelated primes (120 trials). As such, the low propor-
tion of semantically related primes together with a short
prime-target delay (i.e., 200 ms) should ensure that the
task primarily taped into the automatic spreading of acti-
vation (Pomarol-Clotet, Oh, Laws, & McKenna, 2008). All
prime and target words were common nouns (use fre-
quency above 10 per million) according to the Lexique 2
database (New, Pallier, Brysbaert, & Ferrand, 2004). Asso-
ciative matching was realized using the database from
Ferrand (2001). Pseudo-words were created by altering
two letters of an existing common noun. Two lists of stim-
uli were created. Participants received a different list on
each session, which was counterbalanced across day.
Another task including 100 trials (50 pseudo-word targets
and 50 real word targets all preceded by unrelated primes)
was also created for the practice session.
4.5. Results
The analysis of RT in the Eriksen task was performed
after removing errors, responses that were too short
(below 200 ms) and too long (above 1500 ms). A total of
6.5% of the responses were removed. The GLM indicated
only a significant effect of the compatibility with faster
RT for CO than for IN trials, F(1, 20) = 50.137, p< .001,
g
2
= 0.715. Concerning accuracy, a main effect was found
for compatibility with more errors for IN than for CO trials,
F(1, 20) = 63.537, p< .001,
g
2
= 0.761. A main effect of the
time of measurement was also found, with a drop of accu-
racy in time F(1, 20) = 16.800, p< .001,
g
2
= 0.457. A three-
level interaction was found, F(1, 20) = 4.404, p= .049,
g
2
= 0.180. The interaction indicated that for IN stimuli,
there was a drop in accuracy but only for the task requiring
high levels of inhibition, F(1, 20) = 6.774, p= .017,
g
2
= 0.253. All other effects did not reach significance. In
sum, those results indicated that an extended exposure
to a task requiring a high level of inhibition subsequently
impaired the participant’s ability to suppress irrelevant
stimuli.
Concerning the primed LDT, RT below 200 ms and
above 1500 ms were excluded along with all errors (3.4%
overall). As recommended (see Spitzer, Braun, Hermle, &
Maier, 1993 or Morgan et al., 2010), we computed priming
effects by subtracting the RT for related or indirectly
related primes from the RT to unrelated primes. Fig. 2 rep-
resents the mean priming effects for each condition. A 2
(high versus low inhibition conditions) 2 (direct versus
indirect priming) GLM for repeated measures indicated a
main effect of prime relatedness with a bigger priming
effect for directly related primes than indirectly related
primes, F(1, 20) = 24.749, p< .001,
g
2
= 0.553. A significant
effect of this condition was also found, F(1, 20) = 7.51,
p= .013,
g
2
= 0.273. When exposed to the high inhibition
demands task, participants had a greater semantic priming
effect than when exposed to the low inhibition demands
task. A significant interaction was also found, F(1,
116 R. Radel et al. / Cognition 134 (2015) 110–120

20) = 4.753, p= .041,
g
2
= 0.192. Specifically, while there
was no difference between conditions on direct primes
[F(1, 20) = .044, p= .837,
g
2
= 0.002], indirect primes elic-
ited greater priming effects after the task with high inhibi-
tion demands than after the task with low inhibition
demands, F(1, 15) = 10.239, p< .004,
g
2
= 0.339.
5. Discussion
The aim of this study was to assess the effect of reduced
capacity to exert inhibition, induced by an extended
exposure to high inhibition demands, on creativity.
Carson et al. (2003) proposed that low levels of inhibition
are associated with high levels of creativity. The present
series of studies partially support this assumption by show-
ing that performance on fluency (Study 1a and Study 1b),
originality (Study 1a) and flexibity (Study 1b) scores of
the AUT are improved when the resources for inhibition
capacity are depleted. In contrast, performance on the
RAT was not affected. In line with previous studies (e.g.,
Chermahini & Hommel, 2010; White & Shah, 2006), a differ-
ent pattern of results is found for divergent and convergent
Fig. 1. Illustration of the protocol used in Study 1 and Study 2. A conflict task was performed at two different moments to obtain a baseline performance
and to compare this score to the score obtained in the second session performed right after the manipulation (continuous practice on another conflict task).
The session ended with the completion of the creativity tests (RAT and AUT) in the Study 1 and the primed LDT in the study 2. Notes: AUT = Alternate Uses
Task; RAT = Remote Associates Task; Primed LDT = Primed Lexical Decision Task.
R. Radel et al. / Cognition 134 (2015) 110–120 117

creativity tasks. The effects the fluency and originality
scores in the AUT suggest that only idea generation pro-
cesses benefit from a depletion of the resources for inhibi-
tion. This account matches well with previous findings of
the literature, as the consequences of the mental states
associated with an impaired capacity to exert inhibition
(e.g., ADHD, schizophrenia, lateral frontal lesion) have
mostly concerned tasks that are primarily based on original
ideation such as the AUT or on hard insight problem that
require uncommon solutions (e.g., Reverberi, Toraldo,
D’Agostini, & Skrap, 2005). When the creative task also
requires selective attention and inhibitory control, such as
the RAT, these same mental states do not provide any ben-
efits (e.g., White & Shah, 2006). In addition, our results can
be linked to the findings of Chermahini and Hommel (2010)
who showed that spontaneous eye-blink rates were associ-
ated with performance on the AUT, but not on the RAT.
Given that spontaneous eye-blink rate is a marker of central
dopaminergic functioning, and that inhibition is thought to
rely predominantly on dopaminergic activity (Eagle et al.,
2011), this divergence in performance also supports the
role of inhibition in idea generation.
The results of Study 2 provide some insight into the
mechanisms by which disinhibition may impact creativity.
Our results indicate that the manipulation of the inhibition
demands led to a hyper-priming effect for indirect primes.
Given that the magnitude of the indirect priming effect is
considered to be a relevant indicator of the spread of acti-
vation in associative network (Spitzer et al., 1993), our
results suggest a greater spread of activation when the
resources for inhibition are diminished. As such, this result
is in line with previous studies reporting a hyper-priming
effect for indirect primes in conditions of reduced
resources for inhibition, such as thought disorders patients
(for a meta-analysis, see Pomarol-Clotet et al., 2008)or
cannabis intoxication (Morgan et al., 2010). Therefore, we
suggest that the inhibition function may modulate the
spreading of activation in an automatic manner. When
inhibition is impaired, the activation of a concept would
lead to a greater amount of activation in the nodes that
are more closely associated with it. Since inhibition serves
the function of keeping weakly related information out of
working memory, the impairment of this function would
activate a greater number of concepts in working memory
with many of them only weakly related to the initial con-
cept. As explained by Mednick (1962, see also
Martindale, 1995), the activation of a larger range of infor-
mation leads to a greater quantity and originality of ideas.
It is also interesting to note that this can account for the
difficulty to express a coherent and structured stream of
thought among thought disorders patients or after canna-
bis use.
The present research sheds light on our theoretical
understanding of creativity in a number of ways. First,
our work provides a more precise explanation for the
somewhat counterintuitive finding that several mental
states and psychological disorders are associated with high
levels of performance on some types of creativity tasks. It
can also account for the heterogeneity in these results by
proposing that creative performance improves only on
those tasks that predominantly rely on the generation of
ideas, but not on those requiring the integration of con-
straints. Second, we think that the present set of experi-
ments can also help disentangle some inconsistencies in
neuroscience studies of creativity. The recent review by
Dietrich and Kanso (2010) pointed out inconsistencies in
the role of the prefrontal cortex in creative performance.
While some studies clearly showed a positive contribution
of the PFC to creative performance (e.g., Goel & Vartanian,
2005), others showed a deactivation in the PFC during cre-
ative problem solving (e.g., Chrysikou & Thompson-Schill,
2011). Clearly, meaningful interpretations of these findings
require that we distinguish the type of creative task. Even
when this is done, like in the review by Dietrich and Kanso
(2010), inconsistencies persist. For example, Carlsson,
Wendt, and Risberg (2000) reported increased activation
in the PFC among individuals who showed superior perfor-
mance in the AUT. It seems clear that the functions of dif-
ferent regions of the PFC need to be distinguished before
we can have a sense of the role of the prefrontal cortex
in creativity. According to our proposition, the pattern of
activity in the lateral frontal cortex might be of particular
interest to idea generation in these kinds of tasks. Even if
other prefrontal regions are activated, a reduced activity
of the lateral frontal cortex could be associated with
improved performance in divergent tasks. A recent study
of Liu et al. (2012) provided a good illustration. They
reported a decreased activity of the dorso-lateral PFC in
conjunction with an increased activation of the ventro-
medial PFC while participants were improvising during a
lyrical performance. It should be noted that such activity
represents very well the process of idea generation.
The present studies suggest that idea generation
depends in part on the activity of inhibitory control mech-
anisms, probably occurring in lateral frontal region. This
inhibitory control would then modulate the associative
activity among knowledge nodes in regions of the posterior
cortices (see Dietrich, 2004). As suggested by Flaherty
(2005), it seems that regulation in these regions is
Fig. 2. Priming effects as a function of the relatedness of the primes and
the condition in Study 2. Note: Error bars represent the standard errors
from the mean.
118 R. Radel et al. / Cognition 134 (2015) 110–120

mediated through dopaminergic activity. More precisely,
the release of inhibitory mechanisms would facilitate the
penetration of concepts that are less relevant to the current
context in working memory. This might then give rise to
more divergent ideas.
In conclusion, by manipulating the cognitive resources
needed for inhibition, the present paper provides direct
evidence for the link between the inhibition function and
some forms of creativity. This provides a better under-
standing of the role of the inhibition function in the crea-
tive process because it demonstrates that the release of
inhibitory control primarily affects the generation of ideas
through an enlargement of the semantic scope.
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