CREATIVITY RESEARCH JOURNAL, 21(1), 6–14, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1040-0419 print=1532-6934 online
DOI: 10.1080/10400410802633368

The Incubation Effect: Hatching a Solution?
Sophie Ellwood, Gerry Pallier, Allan Snyder, and Jason Gallate

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Centre for the Mind, University of Sydney, Australia

Numerous anecdotal accounts exist of an incubation period promoting creativity andproblem solving. This article examines whether incubation is an empirically verifiablephenomenon and the possible role therein of nonconscious processing. An Idea Generation Test was employed to examine (a) whether an incubation effect occurred and (b) the
impact of different types of break on this effect. In the Idea Generation Test, two groupsof participants were given a distracting break, during which they completed either asimilar or an unrelated task, and a third group worked continuously (N ¼ 90). The Idea
Generation Test was validated against established measures of cognitive ability andpersonality, and was found to exhibit variance distinct from those marker tests. Most
important, results demonstrated that having a break during which one works on acompletely different task is more beneficial for idea production than working on asimilar task or generating ideas continuously. The advantage afforded by a breakcannot be accounted for in terms of relief from functional fixedness or general fatigue,
and, although it may be explicable by relief from task-specific fatigue, explanations ofan incubation effect in terms of nonconscious processing should be (re)considered.

Since the time of Galton, creativity has often been held tobe a crucial component of eminence or genius; however,
the issue of how creativity is to be defined has provencontentious. It is an open question whether there is a
generalizable creative ability or whether the different
instantiations of creativity involve distinct and incommensurable abilities (Hocevar, 1981). Among those who
believe that creativity is unitary, there is disagreement
over whether it can be captured by the construct ofnovelty, or whether the appropriateness of the productshould also be taken into consideration when determining
creativity (e.g., Sternberg & Lubart, 1995). In practice,creativity is often conceived of as a form of problem
solving, with problems being broadly defined as goals tobe reached (Lubart, 2001). Although this approach isbased on a limited view of creative endeavour, it is moreamenable to empirical investigation (than views that
include the esoteric and intangible). The present study
focuses on that conceptualisation by examining an aspectof creativity that would seem to have considerable utility
in everyday life, namely the generation of novel ideas.
Correspondence should be sent to Jason Gallate, Centre for theMind, Main Quadrangle (A14), University of Sydney, Sydney, NSW
2006, Australia. E-mail: jason@centreforthemind.com

There is a considerable overlap between the literatureon creativity and that on problem-solving. Historically,
problem-solving was a focus of theorising by Gestalt psychologists and the idea that sudden awareness of a correct
solution to an unresolved problem demands a psychological explanation appears in the early Gestalt literature(Koffka, 1935=1962). However, it is arguable that Wallas’(1926) model was the most influential from this early period of investigation. Wallas’ model involved four stages:
1. preparation, which involves defining a problem
and consciously attempting to solve it;
2. incubation, wherein, when a solution has notbeen forthcoming, conscious work ceases, but
continues nonconsciously;
3. illumination, which encompasses the moment of
insight; and4. verification, whereby the solution is refined andconfirmed.
Although the preparation and verification stages havebeen the subject of considerable research within bothcognitive and differential psychology, the incubation
phase is somewhat more mysterious, and has proven lessamenable to scientific investigation.

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INCUBATION EFFECT

Anecdotal accounts of creative ideas or solutions‘‘springing to mind’’ after a period of incubation abound,but research on that topic has been comparatively limited.
Despite the paucity of empirical investigations, the majority of studies performed in this field have yielded resultsthat suggest that incubation is a genuine phenomenon thatdemands explanation. Of the approximately 50 studies
that focus on incubation effects, more than 75% haveshown evidence of incubation in at least one of the experimental groups. However, beyond showing that incubation
exists, studies have been methodologically heterogenous.
This has led to much contention in the literature especiallyregarding causes of the incubation effect.
Different studies examine many different facets of the
incubation effect such as: activity before incubation, thetype of problem employed, clues during incubation,
length of the incubation effect, and different activities
employed in the incubation period (Dodds, Ward, &Smith, 2004). Two of these domains were fundamental
to the present study—the type of problem used and theactivity given in the incubation period. These variables
were manipulated in an attempt to test the relative virtues of nonconscious idea generation versus other competing theories, as explanations of the incubation effect.

PROBLEMS WITH CONVERGENTTHINKING TASKS
Although the majority of studies have supported theexistence of an incubation effect, most of those used aconvergent problem-solving task (e.g., Dreistadt, 1969;
Murray & Denny, 1969), whereby individuals have beenaware that they have not found a solution, and thus,
may have still been consciously seeking a resolution.
Even in studies that allow multiple solutions to a single
problem, such as Penney, Godsell, Scott, and Balsom(2004), where the participants were asked to come up
with as many five-letter words as they could from a
10-letter starter word, it is a logical assumption thatthe number of acceptable words is finite. It is also likelythat the participants were aware during the incubation
period that they had not solved, or exhausted, all possibilities to reach a resolution of, the problem. This isimportant because participants may have been consciously, albeit intermittently, working on the problem
while purportedly engaged in other tasks.
It can also be argued that of the minority of convergent
thinking tasks that have not found an incubation effect(e.g., Dominowski, 1972; Dominowski & Jenrick, 1972;
Olton, 1979; Olton & Johnson, 1976) that incubation processes may have still been occurring. Implicit in thesestudies has been the view that incubation can only beevidenced by the achievement of a correct solution. Nevertheless, it may be argued that any ideas produced after

7

conscious work on a problem has ceased could be considered as indicative of the presence of an incubation effect.
The present study used a divergent thinking task,
increasing the likelihood that participants were not consciously working on the problem in the incubation
period for two reasons:
1. There was no problem left unsolved at the end of
the first testing segment. Presumably this leaves
the participant with a sense of resolution, rather
than an insistent feeling that an outstanding
problem needs to be solved.
2. As the task appeared to be completed after the
first testing segment, participants had no reason
to think that they would return to it. (Presumably
these two factors, combined, eliminate any senseof intrinsic reward that might otherwise be gained
from solving an outstanding problem and thus
remove the motivation to consciously work on
the problem).
Both of these propositions are assumptions based on thesubjective experience of the participants, and theauthors highlight that they are not irrefutable facts.
However, to try to verify these assumptions by asking
the participants of their subjective state would be counterproductive to the design of the experiment, not least
because it would require the participant to consciously
think of the task.
Fulgosi and Guilford (1968) pioneered the use of adivergent thinking task in a test of the incubation
effect. They showed that participants came up withmore consequences to a situation after a break involving other cognitive activity than when they wererequired to continuously work on the same problem.
Their results were equivocal, however, because they
only showed a significant effect after a 20-minute incubation period and no effect after a 10-minute incubation effect. Their results were also incapable ofdiscriminating between participants who knew theywould get a second chance at the task and those who
had no indication of this fact. Snyder, Mitchell,
Ellwood, Yates, and Pallier (2004a) revisited the useof a divergent thinking task in a simple design employing an incubation period to assess whether nonconscious idea generation is a possible explanation of the
incubation effect. Participants were required to generate as many possible uses for a piece of paper as they
could. When participants had seemingly exhausted their
supply of ideas, they were told that the task was over,
and were interviewed in order to collect biographicalinformation. Afterwards, to their surprise, participants
were asked once again to provide uses for paper.
Results demonstrated that participants produced aburst of new ideas after the break.

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ELLWOOD, PALLIER, SNYDER, GALLATE

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The possibility that the incubation effect might be theresult of nonconscious idea generation informed the present study. As outlined above, the authors designed thestudy to maximize the possibility that the participants
were not consciously working on the experimental task
during the incubation period. The design also manipulated the tasks employed in the incubation period in
an attempt to discriminate between different putativecauses of the incubation effect. In addition, the discriminant validity of the task, a measure of so-called Ideational Fluency (IF; see Carroll, 1993), was examined inrelation to established measures of personality and tests
of intelligence derived from the framework of the theoryof fluid and crystallized abilities (see, e.g., Horn & Noll,
1994) to see if it was distinct from these constructs.

Problems With Nonconscious Processing
as a Causal Explanation
In cases such as those cited above, where an incubation
effect has purportedly been demonstrated, accounts interms of nonconscious processing have proven contentious (Dorfman, Shames, & Kihlstrom, 1996), partly
because they rely on unobservables (see, e.g., Feldhusen,
1995). Post-behaviorism, many psychologists haveattempted to explain away the incubation effect, claiming that the value of a break lies in enabling recovery
from fatigue, or relief from functional fixedness (Posner,1973). Explanations formulated in terms of recovery
from fatigue state that a break relieves neural fatigue
within an individual, providing them with renewedenergy to attempt a solution. Proponents of functional
fixedness claim that a rest allows individuals to breaktheir mindset, to restructure the problem and approach
it differently, either by ‘‘reducing the ‘recency’ value of
inappropriate strategies,’’ or by selectively forgetting
less useful memories in favor of more relevant ones
(Ochse, 1990, p. 198).
We contend that there is at least as much evidence fornonconscious idea generation as there is for neural fatigue as an explanation of the incubation effect, and thatthe lack of evidence to differentiate these two competingtheories is equally problematic for both. Empirical validation for the neural fatigue theory relies upon something not being evidenced, that is, the putative neuralfiring in the incubation period that would otherwise fatigue the neuron. Although there are direct behavioral
measures of specific neurons decreasing their firing ratein unrelated areas such as pattern discrimination, there
is none for so complicated an area as complex cognition.
Contrastingly, there is abundant evidence of the manifestation of nonconscious processing, because humans
continuously perform behaviors that are not consciously
directed. Similarly, neural firing is recorded throughout

the brain continuously, yet the majority of this activity
does not result in conscious thought.
There are, of course, attendant problems for proposing nonconscious processing as the cause of the incubation effect. There is a conundrum in the behavioral
manifestation of a cause that is, by definition, not discoverable by the individual and not presently objectively
observable by neural imaging.
Theoretical Support for Nonconscious Processing
In addition to the empirical evidence, there are theoretical grounds for asserting nonconscious processing as apossible explanation of the incubation effect. Dorfman
et al. (1996) proposed that implicit memory provides ameans by which to reconceptualize nonconscious processes, making possible the readmission of the study of
incubation to a scientific psychology. Holyoak (1995)
pointed out that the existence of neural networks provides a means of grounding theories of nonconscious
aspects of problem solving. Elaborating on that proposition, Gabora (2002) provided a neural network-inspired
model of creativity. She based her account on the premises that memory is sparse and distributed, in that each
item is stored across many locations, and each location
helps to store many items. Additionally, memory is content-addressable, insofar as each memory is characterized by a specific pattern of excitation and inhibition
across neurons. Associated memories share activationin common. Individuals differ in the richness of theirassociations, or the extent to which their memories overlap. According to Gabora, those with greater associativerichness have access to a larger, more varied number of
responses in creativity tasks.
The current study investigates the incubation effectfrom the perspectives of both individual differencesand experimental cognitive psychology. This makes
possible the examination of whether idea generation isa cognitive ability upon which people differ, which
may contribute to successful life-outcomes, and affords
a greater appreciation of what incubation might involve.
Differential psychologists, generally, have been lessaverse to studying creativity than have modern cognitive
psychologists. According to Ochse (1990), Guilford
articulated the most influential factor-analytical accountof creativity and problem solving, basing his theory on
the existence of distinct cognitive abilities, of which creativity is one. Carroll (1993) examined fluency and creativity factors, particularly those associated with what
Guilford (1967) referred to as ‘‘divergent production.’’In his reanalysis of some 477 data sets, Carroll identified
an Ideational Fluency factor, which included ‘‘tasks inwhich the participant was required to produce, withina fairly liberal time limit, a series of different words orphrases concerned with a specified topic or concept’’INCUBATION EFFECT(p. 396), which is identical to French, Ekstrom, andPrice’s (1963) construct of the same name.
Unlike traditional tests of Ideational Fluency, the test
used in this study included a distracting break halfway
through. That made it possible to establish whether abreak increases response output when, to the participant’s surprise, the task is resumed. To the extent thata break enhances performance, it may be that nonconscious processing or incubation is occurring.
Furthermore, we hypothesized that greater output
would result from a break comprised of a completely
unrelated task over one comprised of a task that taxed
the same resources that would otherwise have been
available to idea generating nonconscious processes.

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METHOD
Participants
Ninety first-year psychology students, with an averageage of 22.0 years, participated as a course requirement.
Sixty-five participants were women. Forty-nine participants were born in Australia and 59 nominated English
as their first language. Participants were recruited forthree conditions: (a) a continuous testing condition;(b) a break condition using a task related to the IF test;and (c) a break condition using a distracting task unrelated to the IF test. There were 30 participants in eachcondition. The experiment was conducted with theapproval of the University’s Human Ethics Committee.
Task Descriptions
Apart from the Idea Generation Test, there were standardised psychometric tests of fluid intelligence (Gf),crystallised intelligence (Gc), long-term memory(TSR). and working memory (SAR), as well as the
OCEANIC personality inventory, a measure of the
Big-Five Factor Model.
Idea generation test. This task was based on
Cattell’s Things Categories Test (French, Ekstrom &Price, 1963), and required participants to list as many
possible different uses for a piece of paper, an item thatis familiar to all. There were three conditions:
1. Continuous, wherein participants were required towork on the task, without a break, for 4 minutes.
2. Controlled Associations had two 2-minute sessions
separated by a break. Participants were interrupted
after 2 minutes, told that the task was over, andrequired to perform the Controlled Associations
Test (details given in the following). That test tookapproximately 5 minutes to complete, after which,9to participants’ surprise, they were requested togenerate new ideas for uses for a piece of paper
for a further 2 minutes.
3. Myers-Briggs Type Indicator (MBTI) also had
two sessions with a break. Participants were interrupted after 2 minutes (as in the controlled associations condition), told the test was over, andasked to complete the MBTI (for 5 minutes) during the break, after which participants wererequested to generate new ideas for uses for a pieceof paper for a further 2 minutes.
Matrices (Gf). In this test (Stankov & Roberts, 2001),
participants were presented with a series of 3 " 3matrices, with all but the bottom right-hand block containing patterns made up of os, þs, and blanks. Participants were required to identify the logical series, and to
fill in the empty square with the appropriate combinationof os, þ s, and blanks to complete the matrix pattern. The
task involved three practice and eleven test items.
Letter swaps (Gf). This test (Stankov & Crawford,
1993) presented participants with three letters (J, K,
and L) in various orders, and required them to carryout mentally a number of letter swaps (e.g., ‘Swap the
1st and 3rd letters’) and identify the resulting order ofletters. There were two practice and 10 test items,
employing 2, 3, 4, or 5 swap operations.
Vocabulary (Gc). In this test (Stankov, 1997), participants were asked to select the most appropriate
definition (from four alternatives) for a series of words.
The test comprised two practice and 10 test items.
Esoteric analogies (Gc). In this test (French et al.,1963), a number of pairs of related words were presented, with participants being required to identify the
relationship between each pair of words and apply it
to select the most appropriate response to a prompt
word (from four alternatives), e.g., Light is to Dark as
Happy is to: Eager, Gay, Sad, Glad. There were twopractice and 10 test items.
Word associations (TSR). This test (French et al.,1963) presented participants with a series of pairs ofwords, and gave them 4 minutes to generate a word thatprovides an association between each pair of words(e.g., Number and Nobility, for which an appropriate
answer would be Count, as people count numbers anda count is a member of the nobility). The test contained
two examples and 10 items.
Controlled associations (purportedly a TSR
measure). In this test (French et al., 1963), participants

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ELLWOOD, PALLIER, SNYDER, GALLATE

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1 minute per word to produce as many synonyms as
possible. The test contained one example and four test
items.
Although Test 6 is currently widely accepted as thedefining task for TSR, it remains unclear from Carroll’s(1993) reanalysis of the position of Test 7, although bothwould appear to share a relationship in Carroll’s
Domain of Idea Production. Interestingly, IF is also
considered part of that Domain and it was hypothesized, from previous studies reported in the literature(e.g., Knoell & Harris, 1952), that Tests 1 and 7 might
define a separate factor from the TSR task.
Paired associates (SAR). In this test (French et al.,1963), participants were given 3 minutes to memorize 15
pairs of first names. They were then presented with thelatter name of each pair, and were given 2 minutes torecall the initial name with which each was associated.
OCEANIC. This personality inventory (Roberts,
2000) required participants to express their level ofagreement (on a five-point Likert scale) with 60
behavioural statements seeking to measure the Big-5
factors of Openness to Experience, Conscientiousness,
Extraversion, Agreeableness, and Neuroticism.
Procedure
Testing was conducted in small groups. Participants
were welcomed, given an overview of the testing session
and informed of their rights under the ethics guidelines.
Informed consent was obtained. They were asked tocomplete forms requesting basic demographic information. In the continuous and MBTI conditions, participants then completed the word associations, controlled
associations, and paired associates tasks, which were
paper and pencil tests timed by the experimenter. Thosein the controlled associations condition completed only
the word associations and paired associates tests, as thecontrolled associations test was reserved for the distracting break in the Idea Generation Test.
Following the paper and pencil tests, participants
completed the computerized OCEANIC inventory
and cognitive abilities tests, which were self-paced.
While they were doing the computerized tests, a second
experimenter (at convenient intervals) took each participant individually to an adjacent room to administer the
Idea Generation Test. An audio recording of responses
for the Idea Generation Test was made so that theexperimenter could check that answers were notreplicated, and the speed of responding was recorded
accurately on a computer. When participants had
finished the session, which took approximately anhour-and-a-half, the experimenter debriefed them andthanked them for their participation.

RESULTS
Descriptive Statistics
The means and standard deviations for each test arepresented in Table 1. As can be seen, none of the tests
revealed floor or ceiling effects. Additionally, the means
and standard deviations are consistent with those of previous studies in our laboratory using the standardized
tests (e.g., Danthiir, Roberts, Pallier, & Stankov,
2001). Similarly, the scores obtained on the OCEANIC
were typical of those previously obtained at the University of Sydney from undergraduate samples.
Correlations Between Variables
In order to establish whether idea generation is a robust
cognitive ability, the pre- and post-break scores werecorrelated. The correlation was 0.65 (p < 0.05), indicating reasonable test-retest reliability and therefore supporting the existence of a reliable cognitive ability.
Moreover, individuals differed considerably on this ability, with scores ranging from 8 to 47. Because the correlation between the two testing sessions was reasonably
substantial, responses were summed and the total score
for idea generation was used in the analyses that follow.
Inspection of Tables 2 and 3 reveals that, generally
speaking, idea generation proved to be independent ofother cognitive abilities and personality traits, with the
exception of controlled associations and matrices, withwhich it correlated 0.28 and 0.21, respectively (p < 0.05
in both cases).
As expected, inspection of Table 2 reveals correlations between the cognitive abilities tests that are, in
general, supportive of Gf=Gc theory.
Inspection of Table 3 reveals no significant relationship between any of the Big-Five dimensions, except

TABLE 1
Descriptive Statistics for the Idea Generation and Cognitive
Abilities Tests
Test
Idea generation
Matrices
Letter swaps
Vocabulary
Esoteric analogies
Word associations
Controlled associations
Paired associates

Mean Accuracy Score

Standard Deviation

22.5
55.4%
77.8%
66.0%
66.8%
28.4%
39.7%
43.4%

8.4
22.1
20.7
18.1
17.1
21.4
15.5
22.3

11

INCUBATION EFFECTTABLE 2
Correlations Between the Idea Generation Test and the Cognitive
Abilities Tests
Test

1

2

3

4

5

6

7

8

1. Idea generation
1
2. Matrices.21 1
3. Letter swaps$.05 .44 1
4. Vocabulary.04 .39 .30 1
5. Esoteric analogies.13 .43 .23 .43 1
6. Word associations.19 .14 .06 .30 .28 1
7. Controlled associations .28 $.04 $.21 $.02 $.05 .05 1
8. Paired associates.08 .21 .20 .35 .27 .40 .24 1

TABLE 4
Pattern Matrix for Principal Components Analysis (With Oblimin
Rotation) of the Idea Generation and Cognitive Abilities Tests
Test

Factor 1

Idea generation
Matrices
Letter swaps
Vocabulary
Esoteric analogies
Word associations
Controlled associations
Paired associates

Factor 2

Factor 3

.87
.85
.73
.46
.57
$.32

$.50
$.31
$.77

.66

$.80

Note. For clarity, only salient loadings (>0.3) are reported.

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Extraversion, where a low (r ¼ 0.22) correlation
appeared. This may be due to the face-to-face natureof the testing procedure.
Exploratory Factor Analysis
In order to further examine the correlations presented
in Table 2, a Principal Components Analysis (withOblimin rotation) was conducted on the idea generationand cognitive abilities tests. It produced a three-factor
solution, presented as Table 4.
These factors were interpreted as follows:
1. Cognitive Ability, defined by establishedmeasures of Gf=Gc, especially tests containing areasoning (Gf) component (matrices, letter
swaps, esoteric analogies, vocabulary, andcontrolled associations);
2. IF, comprising divergent production tasks (idea
generation and controlled associations); and3. Verbal memory, defined by linguistic tasks reliant
on memory (word associations, paired associates,
vocabulary, and esoteric analogies).
Of interest, and as has been reported elsewhere, vocabulary and esoteric analogies proved to be factoriallycomplex in this study (see, e.g., Danthiir et al., 2001;
Pallier, Roberts, & Stankov, 2000), as did controlled
associations.

1

2

3

4

5

As is evident from Table 5, group scores did not differ
significantly in prebreak performance.
Participants produced, on average, 57% as many newideas in the post-break phase as they had in the initial
session, although there were differences in the postbreak response pattern, depending on condition (seeTable 5). These apparent differences were tested via ananalysis of variance (ANOVA).
As can be seen in Table 5, the presence and type of abreak had a substantial effect on the number of ideas
produced in the second half of the task, F(2, 87) ¼ 3.4,
p < .05). Post-hoc Tukey’s HSD tests showed that individuals who undertook the MBTI during a break produced significantly more uses for paper afterwards
than did participants who worked continuously (significant at the .05 level). The other comparisons were notsignificant.
To supplement these findings, effect sizes were calculated using Cohen’s d. A break during which the MBTI
was completed conferred a modest advantage on idea
generation as compared to continuous idea production(d ¼ 0.67; ‘‘medium’’ effect size according to Cohen,
1992). Furthermore, the type of break had a small effect,with MBTI improving performance relative to Controlled Associations (d ¼ 0.44). There was no noteworthy benefit of a break involving Controlled
Associations relative to continuous work (d ¼ 0.16).
TABLE 5
Mean Number of Responses in Each Condition for the Idea
Generation Test

TABLE 3
Correlations Between the Idea Generation Test and Personality
Dimensions
Test

The Effect of a Break on Idea Generation

Time Interval
1. Idea generation
2. Openness
3. Conscientiousness
4. Extraversion
5. Agreeableness6. Neuroticism

1
.10
$.04
.22
$.00
$.01

1
.34
.02
.38
.11

1
.08
.28
.01

PrebreakPostbreak
1
.41
$.39

1
$.10

Continuous

Controlled
Associations

Meyers-Briggs
Type Indicator

14.3
6.9

14.6
7.6

14.4
9.8

6

1

Note. For the Continuous condition, pre-break is the score for the
first two minutes and post-break the score for the second two minutesof work.

12

ELLWOOD, PALLIER, SNYDER, GALLATEDISCUSSION

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The Distinctiveness of the Idea Generation Test
as a Creativity Marker
The Idea Generation Test captures an attribute uponwhich individuals differ considerably, as demonstrated
by the wide variation in the number of responses produced. The moderately strong correlation between the
two testing sessions for idea generation suggests that thisis a relatively stable cognitive ability, and that the test
has reasonable test–retest reliability. Some individuals
excel at idea production, and they continue to do sothroughout the course of the task; others are consistently less fluent.
The distinctness of idea generation, a measure of
Ideational Fluency, from the Cognitive Ability factor isinteresting and somewhat unexpected, as many theorists(e.g., Feldhusen, 1995; Sternberg, 2001) have argued
that intelligence is necessary for ‘‘the development of alarge, fluent knowledge base,’’ which is manipulated invarious ways to solve problems or produce creative ideas(Feldhusen, 1995, p. 255). Also unexpected is the absenceof any meaningful relationship between idea generationand personality. Previous research has suggested a more
substantial link between creativity and extraversion(Martindale & Dailey, 1996), as well as between creativity and openness to experience (Martindale, 1989;
Rawlings, Twomey, Burns, & Morris, 1998). Obviously,
this was not the case in the present study.

Support for Incubation: The Optimum Break
Individuals were generally less productive in the postbreak phase than in the initial session, presumably
because they tended to exhaust their most obvious
responses in the early stages of the test. However, thisperformance decrement was moderated by the existence
and type of break provided. A break in which individuals are occupied on a completely different task
(MBTI) is clearly beneficial compared to working continuously on the same or a similar task (continuous performance and controlled associations, respectively). The
effect size analyses shed further light on this pattern ofresults. Not only is switching to an unrelated task better
than working continuously, but it is also superior to abreak task involving similar cognitive demands.
Performance was enhanced by a break, despite thefact that participants thought the Idea Generation Test
was over, and were engaged on a cognitively demanding
distractor task during the break, precluding conscious
effort. Thus, these results provide support for an incubation effect. Apart from demonstrating the possible
existence of an incubation effect, these findings have
implications for the way in which incubation has

previously been explained. It is apparent that thebenefits of a break are not reducible to relief from functional fixedness. Such accounts postulate that all typesof break from the subject matter of a task should beequally beneficial, as interruptions remove the mindset
perpetuated by specific problem content. On the contrary, the results of the present study suggest that taking
a break from work on a topic is differentially advantageous, and depends on the type of task undertaken
during the break.
These data indicate that it is not merely by providing
relief from general fatigue that a break is effective. Bothconditions involving a break required individuals to workon cognitively demanding (and, thus, fatiguing) distractor tasks. Yet, performance in the MBTI condition wasenhanced, relative to output for those who worked continuously on the Idea Generation Test. Accounts in termsof general fatigue predict that all conditions deployed in
the present study would produce similarly diminishedoutput throughout the course of the task.
Is Idea Generation Occurring Nonconsciously
During the Break?
It is an open question whether the present outcome
constitutes a demonstration of nonconscious idea
generation occurring during the break, or whether it
exemplifies relief from task-specific fatigue (in contrast
to general fatigue, discussed above). Both of thoseaccounts postulate that a break from tasks deploying
the same set of neurophysiological resources should
facilitate performance. This prediction appears to besupported by the results.
The Controlled Associations Test resembles the Idea
Generation Test, insofar as both require individuals to
produce a number of alternative responses related to aparticular topic. They are purported measures of Associational Fluency and Ideational Fluency, respectively,
as characterized by Carroll (1993). In the current study,
those constructs appear to be distinct from TSR, asassessed by the Word Association Test. This procedural
similarity was confirmed by the results of the factor analysis. Although the controlled associations and idea generation tasks differ in content, and are by no means
identical in their processing requirements, it is reasonable to assume that the similarity that exists causes
recruitment of overlapping neural circuits (cf. Gabora,2002). Because of this, the Controlled Associations Test
can be considered to provide only a partial break from
idea generation, whereas the MBTI constitutes acomplete break.
The prediction of the task-specific fatigue and nonconscious processing approaches is the same—after abreak, people generate a greater number of ideas thanthose who work continuously (see Table 5). However,Downloaded By: [University of Sydney] At: 00:48 9 February 2009

INCUBATION EFFECT

the means by which these predictions are derived are distinct. Accounts in terms of nonconscious processing
state that problem-solving can continue during a break,to the extent that neurophysiological resources are available. On the other hand, proponents of the task-specificfatigue approach claim that no such processing occurs
during the break, but that a break involving a distinct
task allows neural circuits to recover from fatigue,
whereas a similar task allows a lesser degree of recovery.
Unfortunately, it is difficult to envisage how to test these
theories differentially using a behavioral approach.
Arguably, this is a matter for neurophysiological investigation, and the research team intends to conduct fMRI
studies to this end.
In common with many studies in this area, theresearch presented here related creativity to idea generation ability. A current limitation of quantifying thisapproach is that it fails to consider the more qualitative
aspects of creative output, which are entailed by the
facets of flexibility and originality. The authors are presently validating a measure designed to (quantitatively)reflect novelty of responses, termed the Creativity Quotient (CQ; Snyder, Mitchell, Bossomaier, & Pallier,
2004b), which marries flexibility and originality in anencompassing metric. CQ is related to French et al.’s(1963) construct of semantic spontaneous flexibility,
which is ‘‘the ability to produce a diversity of verbally
expressed ideas in a situation that is relatively unrestricted’’ (p. 50, italics added), or, in their later scheme,
flexibility of use, which is ‘‘the mental set necessary tothink of different uses for objects’’ (Ekstrom, French,& Harman, 1976, p. 197). At the same time, CQ incorporates a distinction noted by Carroll (1993), by addressing both quantitative and qualitative features of idea
production.
Beyond their role in predicting genius or eminence,tasks such as idea generation have clear potential benefits for educational and industrial and organizational
psychology, particularly as the value of creativity andinnovation to education and corporate success isincreasingly being recognized (Bereiter, 2002; Florida,2002). Future research is directed at ascertaining thepredictive validity of the creativity portrait—a batteryof idea generation tasks broad enough to approximate
Guilford’s (1967) original parameters—in a corporate
context.

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