creative problem solving involves four stages preparation incubation illumination and verification

The Art of Thought: A Pioneering 1926 Model of the Four Stages of Creativity

By maria popova.

Wallas outlines four stages of the creative process — preparation, incubation, illumination, and verification — dancing in a delicate osmosis of conscious and unconscious work. These phases, which literary legend Michael Cowley would come to parallel in his 1958 model of the four stages of writing , go as follows:

1. PREPARATION

During the preparation stage, the problem is “investigated in all directions” as the thinker readies the mental soil for the sowing of the seeds. It’s the accumulation of intellectual resources out of which to construct the new ideas. It is fully conscious and entails part research, part planning, part entering the right frame of mind and attention. Wallas writes:

The educated man has, again, learnt, and can, in the Preparation stage, voluntarily or habitually follow out, rules as to the order in which he shall direct his attention to successive elements.

2. INCUBATION

Next comes a period of unconscious processing, during which no direct effort is exerted upon the problem at hand — this is where the “combinatory play” that marked Einstein’s thought takes place. Wallas notes that the stage has two divergent elements — the “negative fact” that during Incubation we don’t consciously deliberate on a particular problem, and the “positive fact” of a series of unconscious, involuntary (or, as he terms it, “foreconscious” and “forevoluntary”) mental events taking place. He writes:

Voluntary abstention from conscious thought on any problem may, itself, take two forms: the period of abstention may be spent either in conscious mental work on other problems, or in a relaxation from all conscious mental work. The first kind of Incubation economizes time, and is therefore often the better.

T. S. Eliot would come to echo the value of incubation seven years later in his own meditation on the role of idea-incubation in the creative process , as would many other great minds: Alexander Graham Bell, for all his deliberate dedication, spoke of the power of “unconscious cerebration” and Lewis Carroll advocated for the importance of mental “mastication.”

Wallas proposes a technique for optimizing the fruits of the Incubation stage — something our modern-day psychology of productivity would come to confirm — by deliberately building interruptions of concentrated effort into our workflow:

We can often get more result in the same way by beginning several problems in succession, and voluntarily leaving them unfinished while we turn to others, than by finishing our work on each problem at one sitting.

3. ILLUMINATION

Following Incubation is the Illumination stage, which Wallas based on French polymath Henri Poincaré’s concept of “sudden illumination” — that flash of insight that the conscious self can’t will and the subliminal self can only welcome once all elements gathered during the Preparation stage have floated freely around during Incubation and are now ready to click into an illuminating new formation. It is the moment beloved graphic designer Paula Scher likens to the winning alignment of a slot machine , the same kind of “chance-opportunism” masquerading as serendipity that fuels much of scientific discovery.

But, Wallas admonishes, this Illumination can’t be forced:

If we so define the Illumination stage as to restrict it to this instantaneous “flash,” it is obvious that we cannot influence it by a direct effort of will; because we can only bring our will to bear upon psychological events which last for an appreciable time. On the other hand, the final “flash,” or “click” … is the culmination of a successful train of association, which may have lasted for an appreciable time, and which has probably been preceded by a series of tentative and unsuccessful trains. The series of unsuccessful trains of association may last for periods varying from a few seconds to several hours. […] Sometimes the successful train seems to consist of a single leap of association, or of successive leaps which are so rapid as to be almost instantaneous.

Decades later, the great science communicator and MacArthur “genius” Stephen Jay Gould would come to concur that such “trains of association” — connections between the seemingly unconnected — are the secret of genius .

4. VERIFICATION

The last stage, unlike the second and the third, shares with the first a conscious and deliberate effort in the way of testing the validity of the idea and reducing the idea itself to an exact form. Once again borrowing from Poincaré’s pioneering theories, Wallas cites the French polymath:

It never happens that unconscious work supplies ready-made the result of a lengthy calculation in which we only have to apply fixed rules… All that we can hope from these inspirations, which are the fruit of unconscious work, is to obtain points of departure for such calculations. As for the calculations themselves, they must be made in the second period of conscious work which follows the inspiration, and in which the results of the inspiration are verified and the consequences deduced. … They demand discipline, attention, will, and consequently, conscious work.

But perhaps most important of all is the interplay of the stages and the fact that none of them exists in isolation from the rest, for the mechanism of creativity is a complex machine of innumerable, perpetually moving parts. Wallas notes:

In the daily stream of thought these four different stages constantly overlap each other as we explore different problems. An economist reading a Blue Book, a physiologist watching an experiment, or a business man going through his morning’s letters, may at the same time be “incubating” on a problem which he proposed to himself a few days ago, be accumulating knowledge in “preparation” for a second problem, and be “verifying” his conclusions on a third problem. Even in exploring the same problem, the mind may be unconsciously incubating on one aspect of it, while it is consciously employed in preparing for or verifying another aspect. And it must always be remembered that much very important thinking, done for instance by a poet exploring his own memories, or by a man trying to see clearly his emotional relation to his country or his party, resembles musical composition in that the stages leading to success are not very easily fitted into a “problem and solution” scheme. Yet, even when success in thought means the creation of something felt to be beautiful and true rather than the solution of a prescribed problem, the four stages of Preparation, Incubation, Illumination, and the Verification of the final result can generally be distinguished from each other.

The Creativity Question is altogether indispensable and enormously enriching in its entirety, the kind of book you return to again and again. Complement it with this 1939 creative catalyst and its modern-day counterpart .

Public domain images via Flickr Commons

— Published August 28, 2013 — https://www.themarginalian.org/2013/08/28/the-art-of-thought-graham-wallas-stages/ —

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Understanding the four stages of the creative process

There’s a lot that science can teach us about what goes into the creative process—and how each one of us can optimize our own.

How do great artists and innovators come up with their most brilliant ideas ? And by what kind of alchemical process are they able to bring those ideas to life? 

I have eagerly sought the answers to these questions over the past decade of my career as a psychology writer. My fascination with the lives and minds of brilliant artists and innovators has led me on a quest to discover what makes us creative , where ideas come from, and how they come to life. But even after writing an entire book on the science of creativity and designing a creative personality test , there are more questions than answers in my mind. 

Decades of research have yet to uncover the unique spark of creative genius. Creativity is as perplexing to us today as it was to the ancients, who cast creative genius in the realm of the supernatural and declared it the work of the muses.  

What the science does show is that creative people are complex and contradictory. Their creative processes tend to be chaotic and nonlinear—which seems to mirror what’s going on in their brains. Contrary to the “right-brain myth,” creativity doesn’t just involve a single brain region or even a single side of the brain. Instead, the creative process draws on the whole brain. It’s a dynamic interplay of many diverse brain regions, thinking styles, emotions, and unconscious and conscious processing systems coming together in unusual and unexpected ways. 

But while we may never find the formula for creativity, there’s still a lot that science can teach us about what goes into the creative process—and how each one of us can optimize our own. 

Understanding your own creative process

One of the most illuminating things I’ve found is a popular four-stage model of the creative process developed in the 1920s. In his book The Art of Thought , British psychologist Graham Wallas outlined a theory of the creative process based on many years of observing and studying accounts of inventors and other creative types at work. 

The four stages of the creative process: 

Stage 1: preparation.

The creative process begins with preparation: gathering information and materials, identifying sources of inspiration, and acquiring knowledge about the project or problem at hand. This is often an internal process (thinking deeply to generate and engage with ideas) as well as an external one (going out into the world to gather the necessary data, resources, materials, and expertise). 

Stage 2: Incubation

Next, the ideas and information gathered in stage 1 marinate in the mind. As ideas slowly simmer, the work deepens and new connections are formed. During this period of germination, the artist takes their focus off the problem and allows the mind to rest. While the conscious mind wanders, the unconscious engages in what Einstein called “combinatory play”: taking diverse ideas and influences and finding new ways to bring them together. 

Stage 3: Illumination

Next comes the elusive aha moment. After a period of incubation, insights arise from the deeper layers of the mind and break through to conscious awareness, often in a dramatic way. It’s the sudden Eureka! that comes when you’re in the shower, taking a walk, or occupied with something completely unrelated. Seemingly out of nowhere, the solution presents itself. 

Stage 4: Verification

Following the aha moment, the words get written down, the vision is committed to paint or clay, the business plan is developed. Whatever ideas and insights arose in stage 3 are fleshed out and developed. The artist uses critical thinking and aesthetic judgment skills to hone and refine the work and then communicate its value to others. 

Of course, these stages don’t always play out in such an orderly, linear fashion. The creative process tends to look more like a zigzag or spiral than a straight line. The model certainly has its limitations, but it can offer a road map of sorts for our own creative journey, offering a direction, if not a destination. It can help us become more aware of where we’re at in our own process, where we need to go, and the mental processes that can help us get there. And when the process gets a little too messy, coming back to this framework can help us to recenter, realign, and chart the path ahead. 

For instance, if you can’t seem to get from incubation to illumination, the solution might be to go back to stage 1, gathering more resources and knowledge to find that missing element. Or perhaps, in the quest for productivity , you’ve made the all-too-common mistake of skipping straight to stage 4, pushing ahead with a half-baked idea before it’s fully marinated. In that case, carving out time and space for stage 2 may be the necessary detour. 

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How to optimize your creative process for ultimate success

But let’s dig a little deeper: As I’ve contemplated and applied the four-stage model in my own work, I’ve found within it a much more profound insight into the mysteries of creation.  

At its heart, any creative process is about discovering something new within ourselves and then bringing that something into the world for others to experience and enjoy. The work of the artist, the visionary, the innovator is to bridge their inner and outer worlds—taking something that only exists within their own mind and heart and soul and birthing it into concrete, tangible form (you know, not unlike that other kind of creative process). 

Any creative process is a dance between the inner and the outer; the unconscious and conscious mind; dreaming and doing; madness and method; solitary reflection and active collaboration. Psychologists describe it in simple terms of inspiration (coming up with ideas) and generation (bringing ideas to life). 

In the four-stage model, we can see how the internal and external elements of the creative process interact. stages 2 and 3 are all about inspiration: dreaming, reflecting, imagining, opening up to inspiration, and allowing the unconscious mind to do its work. Stages 1 and 4, meanwhile, are about generation: doing the external work of research, planning, execution, and collaboration. Through a dynamic dance of inspiration and generation, brilliant work comes to life. 

How does this help us in our own creative process? The more we master this balance, the more we can tap into our creative potential. We all have a preference for one side over the other, and by becoming more aware of our natural inclinations, we can learn how to optimize our strengths and minimize our weaknesses.  

More inward-focused, idea-generating types excel in stages 2 and 3: getting inspired and coming up with brilliant ideas. But they run the risk of getting stuck in their own heads and failing to materialize their brilliant ideas in the world. These thinkers and dreamers often need to bring more time and focus to stages 1 and 4 in order to keep their creative process on track. Balance inspiration with generation by creating the necessary structures to help you commit to action and put one foot in front of the other to make it happen—or just collaborate with a doer who you can outsource your ideas to! 

Doer types, on the other hand, shine in stages 1 and 4. They’re brilliant at getting things done, but they risk putting all their focus on productivity at the expense of the inner work and big-picture thinking that helps produce truly inspired work. When we bypass the critical work that occurs in the incubation stage, we miss out on our most original and groundbreaking ideas. If you’re a doer/generator, you can up-level your creative process by clearing out the space in your mind and your schedule to dream, imagine, reflect, and contemplate. 

By seeking a balance of these opposing forces, we can bring some order to the chaos of the creative process. And as we become dreamers who do and doers who dream, we empower ourselves to share more of our creative gifts with the world. 

WeWork’s space products including  On Demand ,  All Access , and  dedicated spaces  help businesses of all sizes solve their biggest challenges.

Carolyn Gregoire is a writer and creative consultant living in Brooklyn. She is the co-author of  Wired to Create: Unravelling the Mysteries of the Creative Mind  and the creator of the Creative Types personality test. Her work has been featured in the New York Times, Scientific American, TIME, Harvard Business Review, and other publications.

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• Art and Psychology

Graham Wallas and the Four Stages of the Creative Process

Nessa Bryce

T ake a moment to look at the image above. What do you see? Just a neural network? Perhaps you spotted the hidden figure. If so, you have just had a moment of insight. You may have felt a similar jolt when discovering the solution to a math problem, understanding a joke or metaphor, or realizing something unexpected about yourself. These aha! moments occur when your brain spontaneously reinterprets information to reach a novel, nonobvious conclusion.

I painted Neurons about a decade ago for an art exhibit. I had designed the piece to portray the idea that our brain's neural networks make us who we are. It was only after joining psychologist James T. Enns's vision laboratory at the University of British Columbia in 2013 that I had my own abrupt realization: I recognized how my art could inform science. Using this piece, along with other hidden-object images, I investigated how an individual's focus and attention change when the person is experiencing an unexpected revelation.

For centuries creative individuals have described their sudden breakthroughs, instances when they are able to recombine information in a new and useful way. Scientists view these flashes of insight as markers of the creative process—and observing them in the laboratory elucidates what happens in the brain during problem-solving.

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“A story is emerging about all the factors that lead up to an insight,” says cognitive psychologist John Kounios, who studies creativity at Drexel University.

What researchers are finding is that the contemporary science of creativity largely bolsters an almost century-old theory. In 1926 political scientist Graham Wallas defined the creative process as four distinct stages: preparation, incubation, illumination and verification. Since then, scientists have broken some of his stages into substages to reveal distinct cognitive processes. For example, preparation now consists of two parts, one involving general learning and the other more focused on skill building.

“These stages really seem to be universal, whether you are a scientist, artist, writer or musician,” says Harvard University psychologist Shelley Carson, who has interviewed more than 1,000 creative individuals for her research. And creativity is not restricted to a subset of highly talented artists and thinkers, Carson says. These innovative individuals have a distinct style of thinking, and breaking down their approach can allow anyone to re-create the process. Brain research has revealed that we can all get closer to achieving that magical spark of insight with the help of a few simple techniques.

Stage 1: Explore

Credit: Colin Hayes

Roughly speaking, people solve problems in one of two ways: either they tend to rely on moments of insight, or they prefer to approach things analytically. Answering questions with analysis involves finding solutions through deliberate, methodical trial and error, whereas insight is perceived as an abrupt epiphany. Both methods are useful, but insight is typically seen as the best option for “out of the box” solutions.

In 2008 Kounios and his colleagues monitored the brain activity of 26 study participants using electroencephalography (EEG) while they sat quietly in a room. After recording these electrical signals, the researchers asked the participants to try to solve 180 anagram problems, which involved reorganizing a word, such as “west,” to form another word, such as “stew.” Subjects also reported whether they had used an insightful or analytical approach to solve each problem.

Kounios found that the brain activity of people who used insight differed significantly from that of people who preferred the analytical approach. Before they even began solving problems, most members of the insight group exhibited less activity in the occipital lobe, a region involved in visual processing, compared with the analytical set.

Specifically, the brains in the insight group showed less activity in the so-called alpha-wave range, which reflects neural inhibition, and the beta-1-wave range, which is linked with selective visual attention. In other words, these findings suggest that people who rely on insight tend to experience diffuse visual attention when not actively engaged in a task.

This study, along with Carson's reports from highly creative individuals, suggests that to prime your brain for creativity, you should first wander the world with an open mind. “Gathering a broad base of knowledge is the first stage of the creative process, which usually comes naturally to people through intellectual curiosity,” Carson says. Another way to break your thought habits is by asking questions such as “How can I do this differently?” and by stepping outside your comfort zone. A poet with writer's block, for example, might be advised to take up a new hobby such as scuba diving or dance lessons. Neuroscientist-turned-artist Greg Dunn discovered an entirely different way to depict the brain when he began studying Sumi-e art, an Asian style of painting. His experimentation with the style's free-flowing ink led to a simple yet elegant new method for painting neurons.

Yet simply exposing yourself to new things does not seem to be the full story. According to a study published in early 2018 by Sergio Agnoli and his colleagues at the Marconi Institute for Creativity at the University of Bologna in Italy, how you engage thoughts that arise through new experiences is important for facilitating creativity. They found that individuals who can deliberatively engage in focused mental exploration come up with more original solutions to problems than those who report little ability to control how their mind wanders. Therefore, building a solid foundation from which creativity can grow requires both exposing yourself to new experiences and intentionally engaging with the thoughts and feelings that arise as a result.

Stage 2: Focus

Psychologist Dean Keith Simonton of the University of California, Davis, has linked creativity with the acquisition of expertise. In 2000 Simonton compared the cumulative years of experience of 59 opera composers with their aesthetic success. He measured aesthetic achievement in eight different ways—tallying the number of times an opera w-as recorded and performed in major opera houses, for example, as well as the number of pages devoted to the work in published opera histories.

Simonton found that a composer's years of musical experience were a powerful predictor of an opera's acclaim. He also found that if the composer had already created a number of other works within the same genre, this would actually hurt the opera's critical reception and legacy. In other words, solutions to great problems demand practice, skill and study, yet creative solutions occur when someone applies their experience to new domains.

Whether you are proving Fermat's last theorem or planning a birthday party, finding novel solutions involves a little advance research. How much preparation you need will vary, but the more you know about a problem, the better equipped you will be to solve it.

Some of the most creative minds in history were masters of their respective fields. Considering that these individuals spent large amounts of time immersed in their studies, one of the best ways to maximize your creativity is to find an area in which you would like to develop some expertise. Then begin to follow that passion.

Stage 3: Incubate

Once you have immersed yourself in a problem, the best way to come up with a creative solution is to stop consciously thinking about it. In 2006 Kounios and his colleagues used functional magnetic resonance imaging (fMRI) to record the brain activity of 44 people as they solved 185 remote-association problems. These word puzzles require finding a single word that can turn three seemingly unrelated words into familiar compound phrases; for example, the solution to “foam,” “deep” and “salt” is “sea.” After finding an answer, the subjects reported whether they had solved the problem using insight or analysis.

Kounios found that in the two seconds before a problem appeared, the insight users prepared for the challenge by shifting from their scattered outward attention to an inward focus. Puzzles solved insightfully were preceded by increased activation in the anterior cingulate cortex, a brain region that monitors internal attention to different ideas, among other things. In contrast, tasks solved analytically were preceded by significant activation in the occipital lobe, which, as mentioned earlier, handles visual processing. This increase indicates that the analytical solvers concentrated more on what they were looking at.

Research from the University of Amsterdam and the University of Bologna in Italy has demonstrated that sleeping on a problem or stepping away from it and then immersing yourself in an alternative activity can help you unconsciously cultivate creative solutions.

Taken together, the findings reveal a benefit to forcing your brain to shift gears or look within. One reason might be that your attention can then be captured by a surprising solution your unconscious mind has been ruminating on. So take a nap or try your hand at something new.

History is replete with examples of creative individuals who describe being hit with inspiration while daydreaming or attending to a different task. Writer Robert Louis Stevenson and musician Paul McCartney, for instance, used dreams as starting points for new works. Many day-to-day problems can be solved this way, which explains why so many people recall stumbling on ideas while taking a shower, driving to work or simply walking down the road.

Stage 4: Insight

When insight hits, certain changes happen in the brain. Psychologist Mark Beeman of Northwestern University led a study in 2004 that measured people's brain activity with fMRI and EEG during the moment of insight. As in Kounios's studies, participants tackled remote-association problems and then indicated whether they had cracked the problem by using insight. The results showed significantly increased activity in the anterior superior temporal gyrus of the right hemisphere at the critical moment when the solution appeared, in comparison to problem solvers who did not experience such an aha! moment. This gyrus is a prominent ridge on the cortex of the right hemisphere and plays a fundamental role in recognizing distant connections between words.

The activity surge in the right but not the left lobe may also be meaningful. According to the researchers, there are areas in the right side of your brain that interpret information more loosely than areas in the left side. This means that the information is less tightly defined, allowing you to access other concepts more readily, which is a key component of creativity. Both hemispheres are working all the time, but parts of your right hemisphere might loosely define a cat as a mammal, making it easy to see how a cat relates to, say, an elephant. Parts of your left hemisphere, however, might describe a cat as a small, carnivorous mammal with soft fur, a short snout and retractile claws—something very different from an elephant.

Research has suggested that you can tip the scales toward a looser style of understanding by describing objects or issues in unusual ways. For example, by thinking of a hanger as a long, twisted wire instead of as a metallic instrument for hanging coats, you might discover other uses for it. Try this technique every so often as you are actively working to solve your problem. It might help prime your brain to forge connections between distant concepts.

The moment of insight is also accompanied by a burst of alpha activity in the visual cortex, according to Beeman's study. Alpha activity, as mentioned earlier, inhibits neuron firing, meaning that during a breakthrough, your brain is less involved in processing visual information—perhaps because visual stimuli can be distracting. These findings suggest that you could help your brain discover an insight simply by closing your eyes.

Probably the most famous moment of insight in history is Archimedes' “Eureka!” Legend has it that the ancient Greek mathematician had been challenged to figure out whether a crown that King Hiero II of Syracuse had commissioned was made out of solid gold. Archimedes was preparing a bath when he discovered how to measure an object's volume, and thus its density, after noticing the displacement of water as he climbed into the tub. Although the story may be apocryphal, it has gone down in history in part because it illustrates perfectly how insight strikes.

Stage 5: Follow-Through

Once you have had a moment of insight, you might find yourself feeling elated. A 2013 study by Tufts University researcher Tad Brunyé showed that subjects who came up with broad associations between words, such as associating “pipe” with “flute” rather than with “smoke,” experienced a boost in mood. Take advantage of the positive mood to check whether your solution works. “When you have an insight, it comes with a lot of conviction,” Carson says. “So you really have to be objective and evaluate that idea.”

This stage is an ideal time to bounce ideas off of trusted friends—their feedback and support could help you determine how well your solution works. Do not be discouraged, though, if your personal eureka is less than perfect. Creative people often describe going through many failures before reaching a successful solution. Those failures help to inform the end result, making them a necessary step in the process. When a student asked chemist and two-time Nobel laureate Linus Pauling how he came up with so many good ideas, he replied, “I have a lot of ideas and throw away the bad ones.”

In practice, an individual stage might not always follow easily from the one before it—many people have to revisit earlier steps several times before hitting on inspiration—but ultimately the process can be very rewarding. Creativity does not make only the creators happy; it also benefits all the people who will enjoy their creations.

The joys of an aha! moment may even serve a deeper purpose. In 2013 psychologists Claudia Muth and Claus-Christian Carbon of the University of Bamberg in Germany found that participants who identified a hidden face in a picture liked the image more than those who did not identify the face. Muth hypothesizes that insight is rewarding for evolutionary reasons. She says, “It could explain why we explore the world and why we have interest in things that are new.”

Being curious and pursuing creative endeavors provide you with the opportunity to discover new interests, explore unfamiliar territory, develop expertise and, crucially, take breaks. In short, working to develop and maximize your creativity serves to enrich your life. As Carson puts it, “Once you realize that you can be creative, it opens up this whole new world.”

Nessa Bryce is a clinical psychology Ph.D. candidate at Harvard University. Her work explores how childhood experiences, particularly traumatic ones, shape our brains and thus how we understand and interact with the world around us.

HYPOTHESIS AND THEORY article

Incubation and intuition in creative problem solving.

A commentary has been posted on this article:

Commentary: Incubation and Intuition in Creative Problem Solving

• Read general commentary

• 1 Psychology Department, University of Hertfordshire, Hatfield, UK
• 2 Department of Clinical Sciences, Brunel University London, London, UK

Creative problem solving, in which novel solutions are required, has often been seen as involving a special role for unconscious processes (Unconscious Work) which can lead to sudden intuitive solutions (insights) when a problem is set aside during incubation periods. This notion of Unconscious Work during incubation periods is supported by a review of experimental studies and particularly by studies using the Immediate Incubation paradigm. Other explanations for incubation effects, in terms of Intermittent Work or Beneficial Forgetting are considered. Some recent studies of divergent thinking, using the Alternative Uses task, carried out in my laboratory regarding Immediate vs. Delayed Incubation and the effects of resource competition from interpolated activities are discussed. These studies supported a role for Unconscious Work as against Intermittent Conscious work or Beneficial Forgetting in incubation.

What form might unconscious work take? On theoretical grounds, the notion that Unconscious Work involves the same processing steps as Conscious Work but minus conscious awareness is discounted, despite some recent arguments that the unconscious can duplicate any conscious function. A candidate account in terms of spreading activation, coupled with below-threshold but active goal representations, is put forward. This account could explain the emergence of subjectively sudden intuitive solutions (Aha-insight solutions) as a result of unconscious processes (Unconscious Work) during incubation periods.

“Intuition: the power of the mind by which it immediately perceives the truth of things without reasoning or analysis; a truth so perceived, immediate, instinctive knowledge or belief.

Latin, in , into, upon, and tueri , tuitus , to look.” The Chambers Dictionary, 9 th Edition , 2003, p. 778. Edinburgh: Chambers Harrap.

Creative problem solving involves the production of approaches and solutions that are novel to the solver even if not historically novel ( Boden, 2004 ). Explaining the generation of personally novel solutions is an unresolved issue for the psychology of thinking and problem solving. Sometimes, problems seem to be solved by an immediate intuition or insight (e.g., Salvi et al., 2016 ) but, with difficult problems, a period of conscious analysis is usually needed, even if it does not directly lead to solution and the problem is set aside before solution. Why might setting a problem aside facilitate solution? One popular explanation is that setting creative problems aside for a period can allow unconscious processes to generate solution ideas, which are then experienced, either as spontaneous breakthroughs into consciousness while attention is focussed on other matters, or as very rapid solutions on returning to previously intractable problems. These solutions occurring apparently rapidly and without awareness of intermediate steps, will be experienced as akin to the dictionary idea of an intuition as a truth (a solution in this case) perceived without reasoning or analysis.

The value of setting a problem aside for facilitating solutions has been a concern of theorists in the area for at least the past 100 years. Wallas (1926 , p. 80) drew on Poincaré’s (1910 ) earlier analysis of mathematical creation and labeled the stage in which a problem is not consciously processed as “Incubation.” (It is noteworthy that Poincaré himself did not use the term “Incubation” in his 1910 paper, although he reported four examples of incubation periods from his own experience of creative work in mathematics). In Wallas’s analysis, Incubation is proposed as a useful stage after conscious Preparation but preceding Illumination (or Inspiration) and Verification. Clues to processes underlying creative thinking should be found from analyses of when and why Incubation can be useful. Subjective reports by acknowledged creative thinkers over many areas of work have supported the existence of incubation phenomena (e.g., Poincaré, 1910 ; Ghiselin, 1952 ; Csikszentmihalyi, 1996 ). However, since such personal reports have often been given many years after the events described, the reliability of such reports is highly questionable. For example, frequently cited accounts by Coleridge (composition of poem Kubla Khan in a dream), Mozart (complete compositions coming to mind without error) and Kekulé (discovery of benzene ring in a dream) have proven to be false ( Weisberg, 2006 , pp. 73–78). Poincaré (1910) himself based his own analysis of creative thinking on self reports of problem solving episodes he had experienced nearly 30 years previously. This is actually rather curious, as Poincaré was an active researcher in mathematics at the time of making his analysis of creative thinking and could presumably have drawn on more recent episodes which would be less susceptible to recall problems. However, after Poincaré (1910) and Wallas (1926) , who had relied on their own introspections and on subjective reports by others (e.g., Wallas drew on daydream reports by Varendonck, 1921 ), a substantial body of experimental work research has been carried outusing both (a) insight problems, in which t the solver has to develop a re-structuring of the task to reach a unique solution and (b) divergent problems, that have no single unique solution but in which many novel potential solutions are to be generated. A typical divergent task, often used in research studies, is the Alternative Uses Task. In this task, participants are to produce as many uses as they can which are different from the normal use in response to one or more everyday items, such as a house building brick, a coat hanger, a pencil, a paperclip, and so on ( Guilford, 1967 ; Guilford et al., 1978 ; Gilhooly et al., 2007 ).

Early work on incubation used a laboratory paradigm, known as the Delayed Incubation Paradigm , in which participants work on the target problem for an experimenter set preparation time before being given an interpolated activity different from the target task for a setincubation period before returning to the target problem for a set post-incubation work time. Performance in the incubation condition is compared with that of the control condition in which participants work without a break on the target task for a time equal to the sum of preparation and post-incubation conscious working times in the incubation condition. A recent alternative, the Immediate Incubation paradigm , has an interpolated task immediately after the instructions on the main problem before any conscious work has been undertaken on that problem, followed by uninterrupted work on the maint problem for a set time ( Dijksterhuis and Meurs, 2006 ).

Delayed and Immediate Incubation Effects

There is now considerable evidence from laboratory studies for the benefits of Delayed Incubation, i.e., that setting a problem aside after a period of work is beneficial (see Dodds et al., 2012 , for a qualitative review). A quantitative meta-analysis by Sio and Ormerod (2009) , of 117 studies identified a positive effect of Delayed Incubation, where the overall average effect size was in the low-medium band (mean d = 0.29) over a range of insight and divergent tasks. Sio and Ormerod’s review also revealed that the benefits of an incubation period are greater when participants are occupied by an undemanding interpolated task than when they engage in a demanding interpolated task or no task at all. Overall, from narrative reviews and meta-analysis, it can be concluded that the basic existence of Delayed Incubation effects is clearly established, especially for divergent problem solving.

Concerning the effectiveness of Immediate Incubation opportunities, Dijksterhuis and Nordgren (2006) found that better performances when Immediate Incubation occurred after decision problems or divergent tasks were initially presented. Indeed, Nordgren et al. (2011) reported that Delayed Incubation resulted in better decisions than Immediate Incubation and both types of incubation were beneficial relative to No Incubation.

A meta –analysis ( Strick et al., 2011 ) of 92 decision studies found a significant beneficial aggregate effect size of g = 0.224 for Immediate Incubation. Their results also pointed to a number of moderating factors, for example, beneficial effects were greater, with more options, with shorter presentation times, with shorter incubation times and with induction of a configural mindset vs. a feature based mindset.

In creative divergent tasks Dijksterhuis and Meurs (2006) , reported that responses were more creative on average, when the divergent task instructions were followed immediately by a short distracting task before producing uses for a brick, compared to a control condition. We may note that the instructions in this study did not ask for unusual uses, which is the norm in divergent thinking tasks, and so it is not clear whether participants had the goal of being creative. Participants may have been reporting infrequent uses, that they happened to know, rather than generating uses novel to them at the time of test. Raters tend to score infrequent responses as creative, although such uses may have been pre-known and therefore could reflect memory retrieval rather than generation of subjectively novel responses ( Quellmalz, 1985 ). However, Gilhooly et al. (2012) using more standard instructions with a stress on unusual uses found a stronger beneficial effect of Immediate Incubation than of Delayed Incubation with both incubation effects being superior to control effects, scored for fluency and novelty of responses. Thus, the benefit of immediate incubation was also found when the task involved novelty ( Gilhooly et al., 2012 ) as well as fluency ( Dijksterhuis and Meurs, 2006 ).

Zhong et al. (2008) , applied the Immediate Incubation paradigm to the Remote Associates Task (RAT), in which solvers have to generate an associate common to three words (e.g., cottage, blue, mouse ? Answer : cheese ), and found that, Immediate Incubation activated solution words more on unsolved trials. compared to solution word activation on unsolved trials where that had been no Immediate Incubation.

Overall, it may be concluded from both meta-analyses ( Sio and Ormerod, 2009 ; Strick et al., 2011 ) and from recent studies ( Gilhooly et al., 2012 , 2013 , 2015 ) that incubation periods, whether delayed or immediate, do have beneficial effects. The main theories regarding mechanisms underlying incubation effects will now be outlined.

Theories of Incubation Effects

Intermittent conscious work.

This approach proposes that participants carry out intermittent conscious work during the incubation period despite instructions to be fully engaged on the interpolated task used to fill the incubation period ( Seifert et al., 1995 , p. 82; Weisberg, 2006 , pp. 443–445). Any conscious work during the supposed incubation period would help reduce the time required when the target problem was re-addressed – but conscious work on the target task would be expected to impair performance on the interpolated task. This theory has the merit of parsimony and essentially explains incubation away as not involving any special processes, such as intuitive unconscious thinking.

Beneficial Forgetting

This view (e.g., Woodworth, 1938 ; Simon, 1966 ; Smith and Blankenship, 1991 ; Smith, 1995 ; Segal, 2004 ; see also, Dijksterhuis and Meurs, 2006 ) argues that “mental sets,” weaken during the incubation period. Such “beneficial forgetting” facilitates fresh starts or “set shifting” when the problem is taken up again after the incubation period. As well as decay and interference, misleading approaches may conceivably be weakened through inhibition as proposed in the theory of retrieval-induced forgetting ( Anderson et al., 1994 ; Storm and Angello, 2010 ). Segal (2004) proposed a variant (known as “Fresh Look”) in which simply switching attention away from the main task allowed a new start, with no forgetting or unconscious work proposed. The Fresh Look view does not predict effects of Immediate Incubation because with in that condition, there is insufficient opportunity for sets or fixations to develop that need to be forgotten to enable later progress.

Unconscious Work

On this account incubation effects involve active, but unconscious, or intuitive processing. The term “unconscious work” seems to first appear in the problem solving literature in Poincaré’s (1910 ) paper (p. 328). Related phrases such as “non-conscious idea generation” ( Snyder et al., 2004 ) and “unconscious thought” ( Dijksterhuis and Nordgren, 2006 ; Ritter and Dijksterhuis, 2014 ) are also used in the literature, but I will use the phrase “unconscious work” throughout the present paper.

Theoretically, what form might unconscious work take? For example, could unconscious work be exactly like conscious work, but with just one difference, namely that it is carried out without any conscious awareness? Or is unconscious work better thought of as some form of automatic spreading activation along associative links, as against a conscious rule or strategy governed activity? Wallas (1926) proposed the idea of spreading “associative chains” as being active during incubation, which can be seen as anticipating modern ideas of spreading activation. Poincaré (1910) argued for quite specific mechanisms of automatic idea generation and selection tailored to his domain of interest which was mathematical creation. Both Poincaré and Wallas argued that the suddenness of Illumination or Inspiration coupled with the feeling of confidence in the sudden insight arose from prolonged unconscious work. Wallas’s analysis is often labeled as a Four Stage theory, incorporating Preparation, Incubation, Illumination, and Verification, but he also proposed a sub-stage of Illumination which he dubbed “Intimation” ( Wallas, 1926 , p. 97). This sub-stage is often overlooked in discussions of Wallas’s analysis, although Wallas considered it was important, practically and theoretically (see also, Sadler-Smith, 2015 , for an extended discussion of Intimation in Wallas’s model). Intimation is the moment at the very start of the Illumination period when the solver becomes aware that a flash of success is imminent. Theoretically, Wallas saw Intimation as reflecting increasing activation of a successful association train which was about to become conscious. Thus, Intimation was consistent with the view that Incubation involved unconscious work. Practically, Wallas felt it was important that the solver recognize the Intimation feeling and desist from distracting activities to allow the solution to continue rising into consciousness. Overall, unconscious work has long been favored as a possible explanation of incubation effects. The question of what specific processes might be involved in unconscious work will be considered further in the Theoretical Discussion section.

The possible mechanisms indicated above are not mutually exclusive (or exhaustive). Delayed Incubation could involve all three suggested mechanisms, with some intermittent conscious work taking place when attention strays from the distracting task during the incubation period and with some beneficial forgetting and unconscious work also occurring when the solver is consciously processing to the distracting incubation task. However, a beneficial effect of Immediate Incubation would not be consistent with the Beneficial Forgetting hypothesis in that there is not time in the Immediate paradigm for sets or misleading directions to be established, but the Immediate paradigm would permit some intermittent conscious work and/or some unconscious work.

Theories of Incubation: Empirical Evidence

Intermittent work.

As a check for intermittent conscious work during an incubation period, performance on the interpolated task, during incubation, should be compared with performance by a control group using the interpolated task as a stand-alone activity. Impaired interpolated task performance during incubation would be consistent with the hypothesis of some conscious work on the target task during incubation. The argument here being that intermittent conscious work represents a diversion of resources away from the interpolated task and that should impair performance on the interpolated task. Although this may seem a basic methodological check for intermittent conscious work, it does not appear to have been carried out ( Sio and Ormerod, 2009 ; Dodds et al., 2012 ) until quite recently. In particular, Gilhooly et al. (2012 , 2015 ) incorporated suitable checks for intermittent conscious work on a target divergent thinking task during the incubation period. In an experiment involving delayed and immediate incubation and two different interpolated activities ( Gilhooly et al., 2012 ), there was no evidence of impairment to the interpolated incubation period tasks (which were mental rotations and anagram solving) as a result of the tasks being carried out during incubation periods, as against being carried out as stand-alone tasks in control conditions. These studies also found positive incubation effects, despite a lack of evidence for intermittent conscious work. If anything, the trends in the data were the opposite of those that would be predicted by the intermittent work hypothesis. Mental rotation and anagrams were somewhat (but not significantly) facilitated by being carried out as distractor tasks during incubation. None of the one tail predictions of the intermittent conscious work hypothesis were upheld. An additional analysis examined the correlations between performance scores on the interpolated tasks and post-incubation scores on the target, divergent thinking task. The Intermittent Work Hypothesis would predict negative correlations in that the more attention given to the interpolated task, the better the interpolated task scores would be, and the worse would be the target task scores. Over eight Pearson correlations examined, two were negative and six positive; the average Pearson correlation between target task and interpolated task performance measures was 0.11. Only one correlation was significant ( r = 0.36, p < 0.05, two tail) and this was in the direction opposite to that predicted by the Intermittent Work Hypothesis. This analysis of correlations between interpolated task and target task performance measures thus did not support the Intermittent Work hypothesis. A later study ( Gilhooly et al., 2015 ) using a target divergent thinking task and mental rotations as the interpolated task in a delayed incubation paradigm, also found no impairment in the interpolated task relative to controls. Indeed, mental rotations were significantly better performed as an interpolated task as against as a stand-alone task, contrary to the Intermittent Work Hypothesis.

In a related study, Baird et al. (2012) , using thought monitoring techniques, found that frequency of target task related intermittent thoughts during incubation was not related to quality of performance after the incubation period. So, it seems that even if intermittent thoughts about the target task occurred they were ineffective and did not explain the beneficial effects of incubation. In conclusion, from Baird et al. (2012) and Gilhooly et al. (2012 , 2015 ), it seems safe to rule out the Intermittent Work explanation of incubation effects.

On this view, solvers often develop initial approaches that are misleading and become fixated on these approaches. A break allows such tendencies to become weaker and so a fresh start is possible when the problem is resumed after an incubation break.

Smith (1995) investigated this possibility using word problems presented either with helpful or with misleading cues. After failures to solve, participants were given breaks of varying lengths and then on returning to the task tried to recall the cues and to solve. In the case of misleading cues, participants were more likely to solve when they had forgotten the cues and likelihood of forgetting increased with length of the break. The results thus supported the idea that beneficial forgetting of misleading information could be a factor underlying incubation effects.

Segal (2004) examined a variant of the Beneficial Forgetting approach which may be labeled the Fresh Look hypothesis. On this variant, simply switching attention from the target task is enough and length of break is not important. His study involved a spatial insight problem, in which a square has a parallelogram superimposed on it and the task is to find the sum of the areas of the two shapes. The problem is made easier when the solver realizes that the shapes can be restructured as two equal sided right angle triangles which, if slid, form a rectangle whose area is easily calculated. Participants engaged in this target task until they felt they were experiencing an impasse.

After impasse , participants were given 4 or 12 min on either a demanding verbal task (crossword) or undemanding task (browsing through newspapers) and then returned to the main task for up to 6 more min.

Results indicated significant benefits for incubation break v. no break, but no effects for length of break or for the demandingness of the activity during the break. Segal argued that these results were consistent with a the Fresh Look view, that simply removing attention from the target task was sufficient and that it was not important what was done in the incubation period or how long it was. This study thus supports a role for attentional shifting as a mechanism for Delayed Incubation. Together, Smith (1995) and Segal (2004) are consistent with a role for Beneficial Forgetting in the Delayed Incubation paradigm.

In contrast to Smith (1995) , Segal (2004) , and Dijksterhuis and Meurs (2006) argued that in the Immediate Incubation paradigm, the Beneficial Forgetting approach may be ruled out as there is no period of initial work in which misleading fixations and sets could be developed. Thus, if Immediate Incubation is shown to be effective, the unconscious work hypothesis must remain in contention for Immediate Incubation effects at least and would also be a candidate explanation as one possible mechanism for Delayed Incubation. Dijksterhuis and Meurs (2006) took the beneficial effects of the Immediate Incubation paradigm on a divergent task in their Experiment 3 as support for the role of unconscious work in incubation. However, as already mentioned, the task in this study did not clearly meet the usual criteria for a creative task and the scoring did not distinguish infrequent from genuinely novel responses. Hence, this study did not unequivocally address creative thinking as against free recall of possibly rare but previously experienced events from episodic and semantic memory.

Gilhooly et al. (2012) using explicit instructions to generate novel responses did find that both delayed and immediate incubation were effective in the Alternative Uses task and that immediate incubation produced more facilitation than delayed incubation. These results were consistent with a role for unconscious work in divergent thinking, particularly for Immediate Incubation, to which the Beneficial Forgetting approach is not applicable.

Snyder et al. (2004) investigated the role of unconscious work in the Delayed Incubation paradigm using a surprise return to the target task. In this case, beneficial effects of incubation emerged, consistent with the view that an automatic continuation of work but unconsciously may have occurred after the task was set aside. We may note that Snyder et al.’s (2004) task required simply production of uses for a piece of paper as against novel uses. Thus, this study did not necessarily require creative thinking as against recall of previously known uses.

The interpolated tasks used by Segal (2004) and by Dijksterhuis and Meurs (2006) were different in modality from the main tasks. Segal’s main task was spatial while the interpolated tasks were verbal and Dijksterhuis and Meurs’s study showed the opposite pattern in that their target task was verbal but the interpolated task was spatial. The similarity–dissimilarity relationship between target and interpolated tasks could be important theoretically as the main competing hypotheses suggest different effects of similarity between target and interpolated tasks. If unconscious work is the main process then interpolated tasks similar to the target task should interfere with any unconscious work using the same mental resources and so lead to weaker (or even reversed) incubation effects when compared with effects of dissimilar interpolated tasks. The unconscious work hypothesis suggests that when it comes to incubation it would be helpful to “do something different” from the target task. On the other hand, a forgetting account would suggest that interpolated tasks similar to the target task would cause greater interference, which would lead to more forgetting of misleading approaches and thus enhanced incubation benefits.

Helie et al. (2008) explored the effects of different interpolated tasks on the reminiscence paradigm in free recall. This is relevant to our present concerns because the reminiscence paradigm is analogous to incubation, in that an initial free recall is followed by interpolated tasks for a set period and then the same free recall is attempted a second time. The reminiscence score is the number of items recalled on re-test that were not recalled on the initial free recall. Helie et al. (2008) found that the more executively demanding the interpolated tasks were, the lower were the reminiscence scores for picture recall These results fitted well with Helie and Sun’s (2010) Explicit–Implicit Interaction model which envisages unconscious implicit processes running in parallel with conscious explicit processes. Helie et al.’s (2008) result is consistent with the Unconscious Work hypothesis for incubation in that more demanding interpolated tasks will leave less resources available for unconscious work. However, Helie et al.’s (2008) focus was free recall from episodic memory rather than creative thinking, which requires novel combinations and so, although suggestive, and consistent with Unconscious Work, this result does not directly address creative thinking which is the focus of the present paper.

Ellwood et al. (2009) found a beneficial effect on number of responses post-incubation of a dissimilar interpolated task in a Delayed Incubation experiment. However, this study used a fluency of uses task rather than a novel uses task. Also, as Ellwood et al. (2009) pointed out, although their findings are consistent with an explanation in terms of unconscious work, an explanation in terms of selective relief of fatigue could also be invoked to account for the effects of similarity between incubation and target tasks. On this view, for example, a spatial Delayed Incubation task very different from a main verbal task could facilitate more recovery from fatigue specific to verbal processing than might an interpolated verbal task. Gilhooly et al. (2013) included tests of the effects of the similarity between incubation and target tasks in an Immediate Incubation paradigm, so that where fatigue as an explanation could be examined. The Gilhooly et al. (2013) study factorially varied incubation activities (verbal – anagram solving vs. spatial – mental rotations), used either a clearly creative verbal divergent task (alternate uses) or a clearly spatial divergent task (mental synthesis) and both divergent tasks were scored for novelty as well as fluency. Significant incubation effects were found, but of most interest were the interactions, in that spatial incubation benefitted verbal divergent thinking more than did verbal incubation activity and verbal incubation activity benefitted spatial divergent thinking more than did spatial incubation activity. These results supported a role for unconscious work during incubation periods in creative thinking tasks and did not support the hypotheses that incubation effects are due to Beneficial Forgetting or attention shifting. The Beneficial Forgetting account predicted the opposite pattern of facilitation (i.e., that similar incubation and target tasks would be more beneficial than different modality incubation and target tasks).

Theoretical Discussion

From recent research discussed above relating to the three main explanations for incubation effects, viz., Unconscious Work, Intermittent Work, and Beneficial Forgetting, it seems that given the effectiveness of Immediate Incubation, in which sets are unlikely to have been developed, the Beneficial Forgetting hypothesis can be ruled out for immediate incubation at least. In addition, Gilhooly et al. (2012 , 2015 ) found no support for the idea of Intermittent Work, from studies in which suitable control conditions were included. Unconscious Work thus remains as the best candidate explanation for the effects of Immediate Incubation periods and it handles the effects of similarity between incubation and target task Gilhooly et al. (2013) . Gilhooly et al. (2013) found that Delayed Incubation was beneficial, but less so than Immediate Incubation in a divergent thinking task (Alternative Uses). It could be that in Delayed Incubation, sets do build up during the initial period of conscious work, and are then reduced by Beneficial Forgetting, after which useful unconscious work could come into play. In contrast, with Immediate Incubation, there are no sets to be overcome and beneficial unconscious work can start sooner than in the Delayed paradigm leading to better performance than with Delayed incubation. Overall, however, the Unconscious Work hypothesis is in contention for both Delayed and Immediate Incubation.

However, the question still arises of what processes might be involved in unconscious work? Could unconscious work processes be identical toe conscious work processes with the sole difference that they are executed without conscious awareness? This issue will now be addressed.

Unconscious Work?

Conscious work is generally rule or strategy governed. Could unconscious work also be rule governed? Poincaré (1910 , p. 329) considered the possibility of a “subliminal self” that worked in the same way as the conscious self, but without consciousness, and might even be a superior “self” since it could find solutions that evaded the conscious mind. Kounios and Beeman (2015) illustrate this notion of a subliminal self by supposing that a man has the job of solving long anagrams during office hours. Suppose the person concerned works systematically all day, on the day shift, from 9 am to 5 pm, trying to solve say, “iaiaeiaeiiamsnrtnmhslbtssdtn,” but when he leaves at 5 pm it is still not solved. Another worker takes over and continues the systematic search on the night shift, from where the first worker left off. At 7 pm the night shift worker phones through to the day shift worker with the answer (cf., insight) saying “It’s “antidisestablishmentarianism!””. In this example, the second shift worker represents the unconscious and works just the same way, using systematic search, as the day shift worker; but, the day shift worker is not aware of the night shift worker’s activities until the answer is phoned through.

To explore further the idea that unconscious work might be a subliminal version of conscious work let us consider conscious processing in the Alternate Uses task. This was addressed in a think aloud study of the Brick Uses task by Gilhooly et al. (2007) in which it was found that participants used strategies, such as scanning the target object’s properties (“Bricks are heavy”) and using the retrieved properties to cue and infer uses from semantic memory (“Heavy objects can hold down things like sheets, rugs, tarpaulin and so on, so a heavy brick could do those things too”). Could unconscious work essentially duplicate this form of conscious work but with no awareness. As we have argued previously ( Gilhooly et al., 2012 , p. 976).

“The standard view in cognitive science is (a) that mental contents vary in activation levels, (b) that above some high activation level mental contents become available to consciousness, (c) that we are conscious of only a limited number of highly activated mental elements at any one time (that is, the contents of working memory) and (d) that strategy or rule based processing, as found in Gilhooly et al.’s (2012) think aloud study, requires such highly activated (conscious) material as inputs and generates highly activated (conscious) outputs.”

On the standard view then, conscious work requires the highly activated contents of working memory and highly activated material is necessarily in consciousness. Overall, it seems impossible that unconscious processes could really be exactly like conscious processes in every respect except that of being conscious. For example, using the rules of arithmetic and temporary working memory storage processes to multiply two 3 digit numbers (e.g., 364 × 279 = ?) is surely impossible without highly activated representations in working memory of the numbers, goals, and intermediate results. The short term representations involved in mental arithmetic would seem to be necessarily conscious. It seems impossible to carry out unconscious multiplication of two or three digit numbers. (With practice of course, one can learn and store three digit multiplication results in long term memory which can be directly retrieved by a type of unconscious process. However, this t is not mental multiplication). Poincaré (1910 , p. 334) made a very similar point when he wrote “It never happens that the unconscious work gives us the result of a somewhat long calculation all made , where we only have to apply fixed rules.” In conclusion, the idea that unconscious work or thought processes could be just the same as conscious work processes with the sole difference that they lack awareness of any mental content, seems unlikely.

However, a challenge to this conclusion has been recently put forward by Hassin (2013) who argues in favor of what he labels a “Yes, It Can” (YIC) principle. According to YIC, unconscious processes can perform the same fundamental, high level functions that conscious processes perform. While it would be generally accepted that the elementary (fundamental?) component processes in carrying out 364 × 279 = ?, are unconscious (e.g., the first step of 364 × 279 is likely to be 9 × 4 = 32, which involves a direct retrieval process that occurs without conscious concomitants in adults practiced in basic multiplication at least) and many such steps and processes are needed, yet precise results need to be held in working memory and precise goals need to be formulated in an organized way (executive processes) all of which seems impossible without mental contents activated to conscious levels. Hassin cites some experiments ( Sklar et al., 2012 ) which appear to show priming in subliminally presented additions and subtractions involving two and even three digits. However, these are far from the long calculations with intermediate results that Poincare discussed as difficult for the subliminal self. Exact calculations cannot realistically be made purely by priming which would activates associatively related numbers and not just the correct ones which are needed at every step of a long calculation if it is to be successful. Similar points apply to all types of problem solving which require multiple steps to be carried out and multiple intermediate results to be held along the way between presentation and solution.

Assuming unconscious work cannot actually be just the same in terms of processing steps as conscious work, of what then, might unconscious work consist?

Poincaré (1910 , p. 333) drew on Epicurus’s (341–270 BC) ancient-world theory of atoms as having hooks so that these elementary building blocks of nature could combine with each other. He imagined ideas like hooked atoms hanging on a wall before relevant ideas/atoms are set in motion during Preparation and continue in motion during Incubation. As with molecules of a gas in a container, the atoms/ideas collide at random and sometimes the hooks snag and a new combination is formed. The atoms initially set in motion can strike atoms at rest and may combine with them. This would represent initial ideas being combined with new ideas so that the products of random combination would always have some relation to the starting conditions of the problem.

Campbell (1960) drew on a range of pre-cursors of his view who had stressed the role of extensive trial-and-error in creative work ( Bain, 1874 ; James, 1880 ) and he was strongly influenced by Poincaré (1910) . Campbell argued that creative problem solving involves a quasi-random generation of associations between mental elements (“Blind Variation”) to produce novel combinations of ideas, some of which may be useful and so be subject to Selective Retention. This approach draws an analogy with biological evolution in which random changes in genetic material lead to changes in organisms, some of which are useful and hence retained by natural selection. Similarly, it is argued that ideas are modified in creative problem solving in ways which are blind to the final solution and only by chance lead ultimately to modifications that solve the problem and are retained for future use. Campbell (1960) quoted extensively from Poincaré’s (1910 ) account of creative thinking in mathematics, as involving extensive quasi-random search, although Campbell did not stress any special role for unconscious processing. His concern was very much with the role of blind trial-and-error, whether carried out at a conscious or an unconscious level. It could be argued that Campbell saw productive conscious creative thinking as like the unconscious work proposed by Poincaré (1910) .

Simonton (1995 , 2003 ) developed Campbell’s ideas and used the notion of “mental elements” which are similar to Poincaré’s (1910 ) “hooked atoms.” However, unlike Campbell, Simonton stresses the role of unconscious processes which lead to new combinations, some of which are retained and selected to enter consciousness on the basis of their “stability.”

In terms of current approaches to cognitive processing, how might novel combinations come about? Parallel spreading activation processes in a semantic network could lead to remote and unusual associations ( Jung-Beeman et al., 2004 ). One specific proposal is that of Helie and Sun’s (2010) Explicit–Implicit Interaction model. In this model, incubation is regarded as involving unconscious, implicit, stochastic associative processes that demand little attentional capacity in contrast with conscious explicit rule governed attentionally demanding processes that run in parallel. In this model, activation spreading through implicit networks during incubation periods leads to novel associations which could facilitate later work when conscious processing resumes and the explicit level processes and knowledge interact with the implicit level processes and knowledge. The model does not seem to deal with incubation leading to a breakthrough of solutions into consciousness without an explicit return to the task. According to Dijksterhuis and Nordgren’s (2006) Unconscious Thought Theory (UTT), unconscious thought, or work, is parallel, bottom-up, inexact, and divergent; whereas conscious thought is, serial, exact, and convergent. Thus, the characteristics of unconscious thought, as envisaged by UTT are consistent with incubation effects.

Overall, there is general agreement among many theorists that unconscious thinking, or unconscious work, in the form of implicit associative processes involving spreading activation [similar to Wallas’s (1926) concept of “associative trains”], is a possible explanation of incubation effects.

How might the suddenness of inspiration be explained? Both Poincaré and Wallas saw this feature of creative thinking as indicative of prolonged unconscious work that found a solution and delivered it to consciousness. However, here Poincaré identified a problem for the unconscious work account. How did the good idea become selected for promotion to consciousness? Poincaré was focussed on mathematical creation and he proposed that in this domain selection was based on the mathematician’s special intuitive sensibility to beauty in mathematics and further that the subliminal self possessed this intuitive sensibility. Poincaré’s theory, as stated in the 1910 paper, is narrow in solely addressing mathematical creation; generalization to other fields, such as poetry, music, physics, and so on, would require specific intuitive sensibilities to be proposed for those fields. An alternative possibility that has general applicability, is that when a problem is set aside, a goal representation remains active for extended time periods, although below the threshold for consciousness. The active goal representation would tend to boost activation flow into associated solution-relevant paths and when a solution combination of associations or a single relevant association became active, the solution and the goal representations would mutually activate each other in a positive feedback loop leading both to become conscious as their activations pass threshold levels. It is suggested that this rising activation (or “rising train of association” as Wallas put it) is experienced as Intimation. The present account has the benefit of automaticity and is parsimonious in not requiring special sensibilities to be invoked. The sub-threshold but active goal representation automatically does the work of selecting promising solution –relevant associations.

Concluding Comments and Limitations

Overall, it can be concluded that the field, although still acknowledging the pioneering work of Poincaré and Wallas, has made considerable progress. The existence of incubation as a beneficial stage in creative thinking has been established through a large number of empirical studies ( Sio and Ormerod, 2009 ), so that the field does not depend on potentially unreliable introspective accounts. New paradigms, such as Immediate Incubation have been established and have helped justify a role for implicit Unconscious Work. Theoretical ideas have been sharpened and refined and the joint effects of spreading activation and subconscious goal activation provide a candidate 9 explanation for insight or intuitive solutions following incubation. The approach put forward here, in terms of spreading activation and goal representations, is most applicable to relatively small scale but knowledge rich problems such as divergent thinking tasks. Further work is needed to develop the present approach for knowledge lean problems, such as laboratory insight problems on the one hand and for larger scale real life problems on the other hand.

Author Contributions

The author confirms being the sole contributor of this work and approved it for publication.

This paper is based on research funded by grants from UK Economic and Social Research Council (RES-000-22-2191) and Leverhulme Trust (F008281G) to KG.

Conflict of Interest Statement

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords : creativity, intuition, problem-solving, incubation effect, insight problem solving

Citation: Gilhooly KJ (2016) Incubation and Intuition in Creative Problem Solving. Front. Psychol. 7:1076. doi: 10.3389/fpsyg.2016.01076

Received: 28 April 2016; Accepted: 01 July 2016; Published: 22 July 2016.

Reviewed by:

Copyright © 2016 Gilhooly. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Kenneth J. Gilhooly, [email protected]

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Creative Thinking: Designed for Humans

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The creative thinking processes is complex. Techniques and systems that work at one stage of the process can be detrimental if applied at another stage. This chapter discusses the Four Stages Model of the Creative Thinking Process, and highlights the importance of understanding what occurs within each stage. With this knowledge individuals and organizations can enhance their ability to develop creative ideas.

• Creative thinking processes
• The four stage creative thinking process model: problem definition
• Idea generation
• Idea refinement
• Idea evaluation

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Psychology Discussion

Creative thinking: 4 stages of creativity thinking.

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Some of the stages of creativity thinking are:   1. Preparation 2. Incubation 3. Illumination 4. Verification!

This is also a controlled thinking in which the creative thinker whether artist, writer or a scientist is trying to create something new. It involves characteristics of both reasoning and imagination. Creative thinking is a process in which the individual generates an original, unusual and productive solution to a problem.

It is defined as personal, imaginative thinking which produces a new, novel and useful solution. Unlike ordinary solution to problems, creative solutions are the new one to the effect that other people have not thought before.

The product of creative thinking may be a new and unique way of conceptualizing the world around us. The emphasis in creative thinking is on the word ‘new’. In human beings we find two kinds of productive abilities – the convergent and divergent abilities.

Convergent abilities are used to bring together otherwise divergent things. Divergent production abilities are those which are not guided by rules or conventions, but capable of generating new solutions to a problem. Divergent production abilities are particularly important in creative thinking.

Creative thinking involves four stages:

1. Preparation:

In this stage the thinker formulates the problem and collects the facts and materials considered necessary for finding new solutions. Many times the problem cannot be solved even after days, weeks or months of concentrated efforts. Failing to solve the problem, the thinker turns away from it initiating next stage.

2. Incubation:

During this period some of the ideas that were interfering with the solution will tend to fade. The overt activity and sometimes even thinking about the problem is absent in this stage. But the unconscious thought process involved in creative thinking is at work during this period.

Apparently the thinker will be busy in other activities like reading literature or playing games, etc. Inspite of these activities the contemplation about finding a solution to problem will be going on in the mind.

3. Illumination:

Following the period of incubation the creative ideas occur suddenly. Consequently the obscure thing becomes clear. This sudden flash of solution is known as illumination and is similar to ‘aha (eureka)’ experience. For example, Archimedes found solution to the crown problem.

4. Verification:

Though the solution is found in illumination stage, it is necessary to verify whether that solution is correct or not. Hence in this last stage evaluation of the solution is done. If the solution is not satisfactory the thinker will go back to creative process from the beginning.

If it is satisfactory, the same will be accepted and if necessary, minor modification may also be made in solution.

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• Process of Creative Thinking: 4 Stages | Thinking | Processes | Psychology
• Convergent and Divergent Thinking: Difference | Thinking | Psychology
• Imagination and Creative Art | Psychology
• Essay on Creativity: Meaning, Nature and Stimulation

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Stages of the creative process.

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There are five stages to the creative process: (1) preparation - defining the problem, (2) concentration - focusing on solving the problem, (3) incubation - relaxing and allowing the subconscious mind to work, (4) illumination - the “ah ha” moment where an idea emerges, and (5) verification - ensuring it works and getting others interested.

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The How of Creativity

How creators transform ideas and do something with them..

Posted November 7, 2019 | Reviewed by Hara Estroff Marano

A New Yorker cartoon shows a scene at a cocktail party with a caption: “Did you know that it was Harry who came up with the idea for the daiquiri? He just never did anything with it.”

At the just-concluded thematic conference on individual, social, and educational perspectives on creativity in Dubrovnik, Croatia, my keynote address examined research on bringing creative ideas to life.

Creativity includes not only having ideas, but developing them and transforming them into products or performances. Monet did not just have the idea to paint water lilies or just have the idea to portray changing qualities of light. He also realized these ideas in hundreds of paintings. Tesla did not just have the idea to harness the power of water (although he started by fantasizing about it!), but he built the first hydroelectric power plant.

People usually ask how creative individuals get their ideas. But a better question might be: how do creative individuals realize their ideas? Are creative individuals unusually gritty and just stick with it, no matter what? It turns out they are not.

At least not in the sense that winners of the national spelling bee are gritty and sit doing the same thing over and over again without being swayed by other interests or activities until final success. As grit involves consistency of interests, it tends to help success in more structured activities. In a series of studies, my colleagues and I found that grit does not predict creativity—but visible passion does.

How do people take their ideas and their passion to transform them into products or performances? Here are three things you need to know to get you started.

1. There is no formula for success.

First step: Creativity doesn’t work in steps. Different stages of the creative process have been proposed, including the famous four-stage model by Wallas that describes preparation, incubation, illumination, and verification. Or there's the creative problem-solving model that includes stages called clarify, ideate, develop, and implement. These models have validity, but they don’t represent well-defined and ordered steps.

A necessary starting point is to decide to do something. This is an act of courage. By nature, creativity involves risk—risk that an idea to reorganize a struggling department store would only end in lost customers or risk for one’s reputation if substantial time is spent on a presentation that is ultimately not well received. To demonstrate such courage does not mean to be fearless. Rather, it means deciding to act in spite of feeling uneasy and uncomfortable.

2. Creativity means tweaks and adjustments.

Creators across domains of work—such as art, design, music composition, screenplay writing, and science—usually start with having a relatively vague idea, which changes and develops through the working process. The Pixar movie Up started with an idea about two brothers from a floating city on an alien planet fighting to inherit their father’s kingdom; it ended as the story of an elderly man who ties balloons to his house to fly to South America in order to fulfill a promise to his late wife. To give an example from another domain of work, what is now Flickr started with a game; although Game Neverending did not gain traction, the photo-sharing feature within it developed into a creative response to a consumer need in the early 2000s.

The fact that a creator changes and adjusts an idea based on feedback, constraints, or new knowledge is not a sign of failure. It is a sign of successful creative work. In a classic study, Csikszentmihalyi and Getzels found that most creative art was made not by those who spent the most time executing or crafting their pieces but by those who spent the most time engaging with the objects in their still lives by holding, feeling, arranging, and rearranging them. Csikszentmihalyi deemed this process of what he called “problem finding” as the key feature of creativity, distinguishing it from problem solving, which can be more formulaic in nature.

3. Creativity takes persistence.

Achieving something creative often takes a long time. Artists prepare exhibitions for months, designers go through multiple prototypes and iterations to create a product, scientists take months (or even years) to complete a research project and publish the findings. These paths are not smooth.

When their grant proposal or research paper is rejected, scientists feel disappointed (trust me, I am a scientist). Yet the successful ones are those who persevere. Yitang Zhang spent years thinking about a basic mathematical problem until he was finally able to solve it. When he did, he was skyrocketed from a lecturer to full professor, not to mention receiving the MacArthur (genius) award.

Creative individuals persist in their work, even in the face of uncertainty and obstacles. However, their persistence is often different from what we teach children in schools—to persist through a well-planned set of tasks or steps. Persistence in the creative process is not linear in nature but includes many reformulations and restarts, while keeping in mind the overarching goal even when at times abandoning specific courses of action.

Creative individuals experience many and varied emotions in their work process, from the anxiety of facing an unclear problem to frustration with obstacles to disappointment or even anger at poor reception. Importantly, creative individuals are not necessarily comfortable with risks or impervious to negative feedback. Rather, they are able to persist in their work in spite of such emotional experiences by managing their emotions and channeling them to fuel their work.

Sometimes we have good reasons for not pursuing creative ideas. Maybe you have a full-time job, family, and like to occasionally see friends, and travel. We are not going to develop every idea. But hopefully we do better than Harry who invented the daiquiri but has never done anything with that idea. Knowing what to expect in the creative process might help in managing the stresses and disappointments.

Csikszentmihalyi, M., & Getzels, J. W. (1971). Discovery-oriented behavior and the originality of creative products: a study with artists. Journal of Personality and Social Psychology, 19, 47–52. doi:10.1037/h0031106

Glăveanu, V. P., Lubart, T., Bonnardel, N., Botella, M., de Biaisi, P.-M., Desainte-Catherine, M., Georgsdottir, A., Guillou, K., Kurtag, G.,Mouchiroud, C., Storme, M., Wojtczuk, A., & Zenasni, F. (2013) Creativity as action: Findings from five creative domains. Frontiers in Psychology, 4(176), 1-14. doi:10.3389/fpsyg.2013.00176

Grohman, M., Ivcevic, Z., Silvia, P., & Kaufman, S. B. (2017). The role of passion and persistence in creativity. Psychology in Aesthetics, Creativity and the Arts. 11(4), 376-385. http://dx.doi.org/10.1037/aca0000121

Ivcevic, Z., & Nusbaum, E. C. (2017). From having an idea to doing something with it: Self-regulation for creativity. In M. Karwowski & J. C. Kaufman (Eds.), The creative self: How our beliefs, self-efficacy, mindset, and identity impact our creativity (pp. 343-365). San Diego, CA: Academic Press.

Puccio, G. J., Mance, M., Switalski, L. B., & Reali, P. (2012). Creativity rising. Buffalo, NY: ICSC Press.

Wallas, G. (1926). The art of thought. New York: Harcourt Brace.

Fickr on Wikipedia: https://en.wikipedia.org/wiki/Flickr

Up (Pixar) on Wikipedia: https://en.wikipedia.org/wiki/Up_(2009_film)

https://en.wikipedia.org/wiki/Yitang_Zhang

Zorana Ivcevic Pringle, Ph.D. is a research scientist at the Yale Center for Emotional Intelligence and studies emotions in creativity, as well as how to teach creativity skills through the arts.

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The Four Stages of Creativity: Incubation

This video discusses the incubation effect which is one important steps of the problem solving. And this video is published on Jan 4, 2019 by Micah Buzan. A great idea or the solution to the question may come to us when we are focusing on other things which are completely unrelated. Sometimes we believe that we get the final result after a long period thinking; however, the ideas are suddenly appearing instead of gradually creating. Thus, this curious phenomenon directly separates thinking into consciously thinking and unconsciously thinking. Wallas’ model (1926) describes the four stages of problem solving:

• Preparation, which involves defining a problem and consciously attempting to solve it;
• Incubation, wherein, when a solution has not been forthcoming, conscious work ceases, but continues nonconsciously;
• Illumination, which encompasses the moment of insight;
• Verification, whereby the solution is refined and confirmed.

Ellwood, S., Pallier, G., Snyder, A., & Gallate, J. (January 01, 2009). The Incubation Effect: Hatching a Solution?. Creativity Research Journal, 21, 1, 6-14.

This article (2009) is a scholar journal I found from OSU Library which focus on whether incubation is an empirically verifiable phenomenon and the possible role therein of nonconscious processing. This article set up experiment to find out (a) whether an incubation effect occurred and (b) the impact of different types of break on this effect. Before the experiment set, the article discusses a lot of information which support the exist of incubation effect and its connection with nonconscious processing. The result of experiment demonstrated that having a break during one work which is completely different from your origin work is more beneficial for idea production than working on a similar task.

Savic, M. (September 01, 2015). The incubation effect: How mathematicians recover from proving impasses. Journal of Mathematical Behavior, 39, 67-78.

This article is a scholar journal which mainly discussed how mathematicians respond to, and often overcome “getting stuck.” And it made a long period experiment to investigate that what they will do when they are getting stuck and whether the action of mathematicians deliberate or accidental. According to the article, author find that six mathematicians used their own ways to try to overcome their impasse, for example, doing tasks unrelated to mathematics or sleeping on it. What’s more, it provides some future research which related to how to apply incubation effect to the school education. It provides some points for school to help students study more efficient.

IRVINE, W. B. (2017). AHA!: The moments of insight that shape our world. S.l.: OXFORD UNIVERSITY PRESS.

This book uses five different domains to study how the Aha Moment happen in the different domains on the different ways. The author describes some great Aha Moment in history. The part 4 of this book is The Aha Moment in Mathematics. It provides a lot of story of mathematicians and claims that the Aha moment which is the production of unconsciously thinking plays a what wonderful role in their problem solving process. It implies that a mathematician’s unconscious mind is better at math than his conscious mind! This book lists a lot of stories about different mathematicians, but there is common that they are very glad to have an Aha Moment which can help them overcome the impasses. Their emotion expression shows that Aha Moment, or incubation effect, have played an important role in their work. In the process of solving problem, after they try their best to understand and solve the problem, incubation will help mathematicians at some degree. This book doesn’t base on the psychology’s complicated experiment, thus it more focus on analyzing.

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Incubation and Intuition in Creative Problem Solving

Kenneth j. gilhooly.

1 Psychology Department, University of Hertfordshire, Hatfield, UK

2 Department of Clinical Sciences, Brunel University London, London, UK

Creative problem solving, in which novel solutions are required, has often been seen as involving a special role for unconscious processes (Unconscious Work) which can lead to sudden intuitive solutions (insights) when a problem is set aside during incubation periods. This notion of Unconscious Work during incubation periods is supported by a review of experimental studies and particularly by studies using the Immediate Incubation paradigm. Other explanations for incubation effects, in terms of Intermittent Work or Beneficial Forgetting are considered. Some recent studies of divergent thinking, using the Alternative Uses task, carried out in my laboratory regarding Immediate vs. Delayed Incubation and the effects of resource competition from interpolated activities are discussed. These studies supported a role for Unconscious Work as against Intermittent Conscious work or Beneficial Forgetting in incubation.

“Intuition: the power of the mind by which it immediately perceives the truth of things without reasoning or analysis; a truth so perceived, immediate, instinctive knowledge or belief.

Latin, in , into, upon, and tueri , tuitus , to look.” The Chambers Dictionary, 9 th Edition , 2003, p. 778. Edinburgh: Chambers Harrap.

Creative problem solving involves the production of approaches and solutions that are novel to the solver even if not historically novel ( Boden, 2004 ). Explaining the generation of personally novel solutions is an unresolved issue for the psychology of thinking and problem solving. Sometimes, problems seem to be solved by an immediate intuition or insight (e.g., Salvi et al., 2016 ) but, with difficult problems, a period of conscious analysis is usually needed, even if it does not directly lead to solution and the problem is set aside before solution. Why might setting a problem aside facilitate solution? One popular explanation is that setting creative problems aside for a period can allow unconscious processes to generate solution ideas, which are then experienced, either as spontaneous breakthroughs into consciousness while attention is focussed on other matters, or as very rapid solutions on returning to previously intractable problems. These solutions occurring apparently rapidly and without awareness of intermediate steps, will be experienced as akin to the dictionary idea of an intuition as a truth (a solution in this case) perceived without reasoning or analysis.

The value of setting a problem aside for facilitating solutions has been a concern of theorists in the area for at least the past 100 years. Wallas (1926 , p. 80) drew on Poincaré’s (1910 ) earlier analysis of mathematical creation and labeled the stage in which a problem is not consciously processed as “Incubation.” (It is noteworthy that Poincaré himself did not use the term “Incubation” in his 1910 paper, although he reported four examples of incubation periods from his own experience of creative work in mathematics). In Wallas’s analysis, Incubation is proposed as a useful stage after conscious Preparation but preceding Illumination (or Inspiration) and Verification. Clues to processes underlying creative thinking should be found from analyses of when and why Incubation can be useful. Subjective reports by acknowledged creative thinkers over many areas of work have supported the existence of incubation phenomena (e.g., Poincaré, 1910 ; Ghiselin, 1952 ; Csikszentmihalyi, 1996 ). However, since such personal reports have often been given many years after the events described, the reliability of such reports is highly questionable. For example, frequently cited accounts by Coleridge (composition of poem Kubla Khan in a dream), Mozart (complete compositions coming to mind without error) and Kekulé (discovery of benzene ring in a dream) have proven to be false ( Weisberg, 2006 , pp. 73–78). Poincaré (1910) himself based his own analysis of creative thinking on self reports of problem solving episodes he had experienced nearly 30 years previously. This is actually rather curious, as Poincaré was an active researcher in mathematics at the time of making his analysis of creative thinking and could presumably have drawn on more recent episodes which would be less susceptible to recall problems. However, after Poincaré (1910) and Wallas (1926) , who had relied on their own introspections and on subjective reports by others (e.g., Wallas drew on daydream reports by Varendonck, 1921 ), a substantial body of experimental work research has been carried outusing both (a) insight problems, in which t the solver has to develop a re-structuring of the task to reach a unique solution and (b) divergent problems, that have no single unique solution but in which many novel potential solutions are to be generated. A typical divergent task, often used in research studies, is the Alternative Uses Task. In this task, participants are to produce as many uses as they can which are different from the normal use in response to one or more everyday items, such as a house building brick, a coat hanger, a pencil, a paperclip, and so on ( Guilford, 1967 ; Guilford et al., 1978 ; Gilhooly et al., 2007 ).

Early work on incubation used a laboratory paradigm, known as the Delayed Incubation Paradigm , in which participants work on the target problem for an experimenter set preparation time before being given an interpolated activity different from the target task for a setincubation period before returning to the target problem for a set post-incubation work time. Performance in the incubation condition is compared with that of the control condition in which participants work without a break on the target task for a time equal to the sum of preparation and post-incubation conscious working times in the incubation condition. A recent alternative, the Immediate Incubation paradigm , has an interpolated task immediately after the instructions on the main problem before any conscious work has been undertaken on that problem, followed by uninterrupted work on the maint problem for a set time ( Dijksterhuis and Meurs, 2006 ).

Delayed and Immediate Incubation Effects

There is now considerable evidence from laboratory studies for the benefits of Delayed Incubation, i.e., that setting a problem aside after a period of work is beneficial (see Dodds et al., 2012 , for a qualitative review). A quantitative meta-analysis by Sio and Ormerod (2009) , of 117 studies identified a positive effect of Delayed Incubation, where the overall average effect size was in the low-medium band (mean d = 0.29) over a range of insight and divergent tasks. Sio and Ormerod’s review also revealed that the benefits of an incubation period are greater when participants are occupied by an undemanding interpolated task than when they engage in a demanding interpolated task or no task at all. Overall, from narrative reviews and meta-analysis, it can be concluded that the basic existence of Delayed Incubation effects is clearly established, especially for divergent problem solving.

Concerning the effectiveness of Immediate Incubation opportunities, Dijksterhuis and Nordgren (2006) found that better performances when Immediate Incubation occurred after decision problems or divergent tasks were initially presented. Indeed, Nordgren et al. (2011) reported that Delayed Incubation resulted in better decisions than Immediate Incubation and both types of incubation were beneficial relative to No Incubation.

A meta –analysis ( Strick et al., 2011 ) of 92 decision studies found a significant beneficial aggregate effect size of g = 0.224 for Immediate Incubation. Their results also pointed to a number of moderating factors, for example, beneficial effects were greater, with more options, with shorter presentation times, with shorter incubation times and with induction of a configural mindset vs. a feature based mindset.

In creative divergent tasks Dijksterhuis and Meurs (2006) , reported that responses were more creative on average, when the divergent task instructions were followed immediately by a short distracting task before producing uses for a brick, compared to a control condition. We may note that the instructions in this study did not ask for unusual uses, which is the norm in divergent thinking tasks, and so it is not clear whether participants had the goal of being creative. Participants may have been reporting infrequent uses, that they happened to know, rather than generating uses novel to them at the time of test. Raters tend to score infrequent responses as creative, although such uses may have been pre-known and therefore could reflect memory retrieval rather than generation of subjectively novel responses ( Quellmalz, 1985 ). However, Gilhooly et al. (2012) using more standard instructions with a stress on unusual uses found a stronger beneficial effect of Immediate Incubation than of Delayed Incubation with both incubation effects being superior to control effects, scored for fluency and novelty of responses. Thus, the benefit of immediate incubation was also found when the task involved novelty ( Gilhooly et al., 2012 ) as well as fluency ( Dijksterhuis and Meurs, 2006 ).

Zhong et al. (2008) , applied the Immediate Incubation paradigm to the Remote Associates Task (RAT), in which solvers have to generate an associate common to three words (e.g., cottage, blue, mouse ? Answer : cheese ), and found that, Immediate Incubation activated solution words more on unsolved trials. compared to solution word activation on unsolved trials where that had been no Immediate Incubation.

Overall, it may be concluded from both meta-analyses ( Sio and Ormerod, 2009 ; Strick et al., 2011 ) and from recent studies ( Gilhooly et al., 2012 , 2013 , 2015 ) that incubation periods, whether delayed or immediate, do have beneficial effects. The main theories regarding mechanisms underlying incubation effects will now be outlined.

Theories of Incubation Effects

Intermittent conscious work.

This approach proposes that participants carry out intermittent conscious work during the incubation period despite instructions to be fully engaged on the interpolated task used to fill the incubation period ( Seifert et al., 1995 , p. 82; Weisberg, 2006 , pp. 443–445). Any conscious work during the supposed incubation period would help reduce the time required when the target problem was re-addressed – but conscious work on the target task would be expected to impair performance on the interpolated task. This theory has the merit of parsimony and essentially explains incubation away as not involving any special processes, such as intuitive unconscious thinking.

Beneficial Forgetting

This view (e.g., Woodworth, 1938 ; Simon, 1966 ; Smith and Blankenship, 1991 ; Smith, 1995 ; Segal, 2004 ; see also, Dijksterhuis and Meurs, 2006 ) argues that “mental sets,” weaken during the incubation period. Such “beneficial forgetting” facilitates fresh starts or “set shifting” when the problem is taken up again after the incubation period. As well as decay and interference, misleading approaches may conceivably be weakened through inhibition as proposed in the theory of retrieval-induced forgetting ( Anderson et al., 1994 ; Storm and Angello, 2010 ). Segal (2004) proposed a variant (known as “Fresh Look”) in which simply switching attention away from the main task allowed a new start, with no forgetting or unconscious work proposed. The Fresh Look view does not predict effects of Immediate Incubation because with in that condition, there is insufficient opportunity for sets or fixations to develop that need to be forgotten to enable later progress.

Unconscious Work

On this account incubation effects involve active, but unconscious, or intuitive processing. The term “unconscious work” seems to first appear in the problem solving literature in Poincaré’s (1910 ) paper (p. 328). Related phrases such as “non-conscious idea generation” ( Snyder et al., 2004 ) and “unconscious thought” ( Dijksterhuis and Nordgren, 2006 ; Ritter and Dijksterhuis, 2014 ) are also used in the literature, but I will use the phrase “unconscious work” throughout the present paper.

Theoretically, what form might unconscious work take? For example, could unconscious work be exactly like conscious work, but with just one difference, namely that it is carried out without any conscious awareness? Or is unconscious work better thought of as some form of automatic spreading activation along associative links, as against a conscious rule or strategy governed activity? Wallas (1926) proposed the idea of spreading “associative chains” as being active during incubation, which can be seen as anticipating modern ideas of spreading activation. Poincaré (1910) argued for quite specific mechanisms of automatic idea generation and selection tailored to his domain of interest which was mathematical creation. Both Poincaré and Wallas argued that the suddenness of Illumination or Inspiration coupled with the feeling of confidence in the sudden insight arose from prolonged unconscious work. Wallas’s analysis is often labeled as a Four Stage theory, incorporating Preparation, Incubation, Illumination, and Verification, but he also proposed a sub-stage of Illumination which he dubbed “Intimation” ( Wallas, 1926 , p. 97). This sub-stage is often overlooked in discussions of Wallas’s analysis, although Wallas considered it was important, practically and theoretically (see also, Sadler-Smith, 2015 , for an extended discussion of Intimation in Wallas’s model). Intimation is the moment at the very start of the Illumination period when the solver becomes aware that a flash of success is imminent. Theoretically, Wallas saw Intimation as reflecting increasing activation of a successful association train which was about to become conscious. Thus, Intimation was consistent with the view that Incubation involved unconscious work. Practically, Wallas felt it was important that the solver recognize the Intimation feeling and desist from distracting activities to allow the solution to continue rising into consciousness. Overall, unconscious work has long been favored as a possible explanation of incubation effects. The question of what specific processes might be involved in unconscious work will be considered further in the Theoretical Discussion section.

The possible mechanisms indicated above are not mutually exclusive (or exhaustive). Delayed Incubation could involve all three suggested mechanisms, with some intermittent conscious work taking place when attention strays from the distracting task during the incubation period and with some beneficial forgetting and unconscious work also occurring when the solver is consciously processing to the distracting incubation task. However, a beneficial effect of Immediate Incubation would not be consistent with the Beneficial Forgetting hypothesis in that there is not time in the Immediate paradigm for sets or misleading directions to be established, but the Immediate paradigm would permit some intermittent conscious work and/or some unconscious work.

Theories of Incubation: Empirical Evidence

Intermittent work.

As a check for intermittent conscious work during an incubation period, performance on the interpolated task, during incubation, should be compared with performance by a control group using the interpolated task as a stand-alone activity. Impaired interpolated task performance during incubation would be consistent with the hypothesis of some conscious work on the target task during incubation. The argument here being that intermittent conscious work represents a diversion of resources away from the interpolated task and that should impair performance on the interpolated task. Although this may seem a basic methodological check for intermittent conscious work, it does not appear to have been carried out ( Sio and Ormerod, 2009 ; Dodds et al., 2012 ) until quite recently. In particular, Gilhooly et al. (2012 , 2015 ) incorporated suitable checks for intermittent conscious work on a target divergent thinking task during the incubation period. In an experiment involving delayed and immediate incubation and two different interpolated activities ( Gilhooly et al., 2012 ), there was no evidence of impairment to the interpolated incubation period tasks (which were mental rotations and anagram solving) as a result of the tasks being carried out during incubation periods, as against being carried out as stand-alone tasks in control conditions. These studies also found positive incubation effects, despite a lack of evidence for intermittent conscious work. If anything, the trends in the data were the opposite of those that would be predicted by the intermittent work hypothesis. Mental rotation and anagrams were somewhat (but not significantly) facilitated by being carried out as distractor tasks during incubation. None of the one tail predictions of the intermittent conscious work hypothesis were upheld. An additional analysis examined the correlations between performance scores on the interpolated tasks and post-incubation scores on the target, divergent thinking task. The Intermittent Work Hypothesis would predict negative correlations in that the more attention given to the interpolated task, the better the interpolated task scores would be, and the worse would be the target task scores. Over eight Pearson correlations examined, two were negative and six positive; the average Pearson correlation between target task and interpolated task performance measures was 0.11. Only one correlation was significant ( r = 0.36, p < 0.05, two tail) and this was in the direction opposite to that predicted by the Intermittent Work Hypothesis. This analysis of correlations between interpolated task and target task performance measures thus did not support the Intermittent Work hypothesis. A later study ( Gilhooly et al., 2015 ) using a target divergent thinking task and mental rotations as the interpolated task in a delayed incubation paradigm, also found no impairment in the interpolated task relative to controls. Indeed, mental rotations were significantly better performed as an interpolated task as against as a stand-alone task, contrary to the Intermittent Work Hypothesis.

In a related study, Baird et al. (2012) , using thought monitoring techniques, found that frequency of target task related intermittent thoughts during incubation was not related to quality of performance after the incubation period. So, it seems that even if intermittent thoughts about the target task occurred they were ineffective and did not explain the beneficial effects of incubation. In conclusion, from Baird et al. (2012) and Gilhooly et al. (2012 , 2015 ), it seems safe to rule out the Intermittent Work explanation of incubation effects.

On this view, solvers often develop initial approaches that are misleading and become fixated on these approaches. A break allows such tendencies to become weaker and so a fresh start is possible when the problem is resumed after an incubation break.

Smith (1995) investigated this possibility using word problems presented either with helpful or with misleading cues. After failures to solve, participants were given breaks of varying lengths and then on returning to the task tried to recall the cues and to solve. In the case of misleading cues, participants were more likely to solve when they had forgotten the cues and likelihood of forgetting increased with length of the break. The results thus supported the idea that beneficial forgetting of misleading information could be a factor underlying incubation effects.

Segal (2004) examined a variant of the Beneficial Forgetting approach which may be labeled the Fresh Look hypothesis. On this variant, simply switching attention from the target task is enough and length of break is not important. His study involved a spatial insight problem, in which a square has a parallelogram superimposed on it and the task is to find the sum of the areas of the two shapes. The problem is made easier when the solver realizes that the shapes can be restructured as two equal sided right angle triangles which, if slid, form a rectangle whose area is easily calculated. Participants engaged in this target task until they felt they were experiencing an impasse.

After impasse , participants were given 4 or 12 min on either a demanding verbal task (crossword) or undemanding task (browsing through newspapers) and then returned to the main task for up to 6 more min.

Results indicated significant benefits for incubation break v. no break, but no effects for length of break or for the demandingness of the activity during the break. Segal argued that these results were consistent with a the Fresh Look view, that simply removing attention from the target task was sufficient and that it was not important what was done in the incubation period or how long it was. This study thus supports a role for attentional shifting as a mechanism for Delayed Incubation. Together, Smith (1995) and Segal (2004) are consistent with a role for Beneficial Forgetting in the Delayed Incubation paradigm.

In contrast to Smith (1995) , Segal (2004) , and Dijksterhuis and Meurs (2006) argued that in the Immediate Incubation paradigm, the Beneficial Forgetting approach may be ruled out as there is no period of initial work in which misleading fixations and sets could be developed. Thus, if Immediate Incubation is shown to be effective, the unconscious work hypothesis must remain in contention for Immediate Incubation effects at least and would also be a candidate explanation as one possible mechanism for Delayed Incubation. Dijksterhuis and Meurs (2006) took the beneficial effects of the Immediate Incubation paradigm on a divergent task in their Experiment 3 as support for the role of unconscious work in incubation. However, as already mentioned, the task in this study did not clearly meet the usual criteria for a creative task and the scoring did not distinguish infrequent from genuinely novel responses. Hence, this study did not unequivocally address creative thinking as against free recall of possibly rare but previously experienced events from episodic and semantic memory.

Gilhooly et al. (2012) using explicit instructions to generate novel responses did find that both delayed and immediate incubation were effective in the Alternative Uses task and that immediate incubation produced more facilitation than delayed incubation. These results were consistent with a role for unconscious work in divergent thinking, particularly for Immediate Incubation, to which the Beneficial Forgetting approach is not applicable.

Snyder et al. (2004) investigated the role of unconscious work in the Delayed Incubation paradigm using a surprise return to the target task. In this case, beneficial effects of incubation emerged, consistent with the view that an automatic continuation of work but unconsciously may have occurred after the task was set aside. We may note that Snyder et al.’s (2004) task required simply production of uses for a piece of paper as against novel uses. Thus, this study did not necessarily require creative thinking as against recall of previously known uses.

The interpolated tasks used by Segal (2004) and by Dijksterhuis and Meurs (2006) were different in modality from the main tasks. Segal’s main task was spatial while the interpolated tasks were verbal and Dijksterhuis and Meurs’s study showed the opposite pattern in that their target task was verbal but the interpolated task was spatial. The similarity–dissimilarity relationship between target and interpolated tasks could be important theoretically as the main competing hypotheses suggest different effects of similarity between target and interpolated tasks. If unconscious work is the main process then interpolated tasks similar to the target task should interfere with any unconscious work using the same mental resources and so lead to weaker (or even reversed) incubation effects when compared with effects of dissimilar interpolated tasks. The unconscious work hypothesis suggests that when it comes to incubation it would be helpful to “do something different” from the target task. On the other hand, a forgetting account would suggest that interpolated tasks similar to the target task would cause greater interference, which would lead to more forgetting of misleading approaches and thus enhanced incubation benefits.

Helie et al. (2008) explored the effects of different interpolated tasks on the reminiscence paradigm in free recall. This is relevant to our present concerns because the reminiscence paradigm is analogous to incubation, in that an initial free recall is followed by interpolated tasks for a set period and then the same free recall is attempted a second time. The reminiscence score is the number of items recalled on re-test that were not recalled on the initial free recall. Helie et al. (2008) found that the more executively demanding the interpolated tasks were, the lower were the reminiscence scores for picture recall These results fitted well with Helie and Sun’s (2010) Explicit–Implicit Interaction model which envisages unconscious implicit processes running in parallel with conscious explicit processes. Helie et al.’s (2008) result is consistent with the Unconscious Work hypothesis for incubation in that more demanding interpolated tasks will leave less resources available for unconscious work. However, Helie et al.’s (2008) focus was free recall from episodic memory rather than creative thinking, which requires novel combinations and so, although suggestive, and consistent with Unconscious Work, this result does not directly address creative thinking which is the focus of the present paper.

Ellwood et al. (2009) found a beneficial effect on number of responses post-incubation of a dissimilar interpolated task in a Delayed Incubation experiment. However, this study used a fluency of uses task rather than a novel uses task. Also, as Ellwood et al. (2009) pointed out, although their findings are consistent with an explanation in terms of unconscious work, an explanation in terms of selective relief of fatigue could also be invoked to account for the effects of similarity between incubation and target tasks. On this view, for example, a spatial Delayed Incubation task very different from a main verbal task could facilitate more recovery from fatigue specific to verbal processing than might an interpolated verbal task. Gilhooly et al. (2013) included tests of the effects of the similarity between incubation and target tasks in an Immediate Incubation paradigm, so that where fatigue as an explanation could be examined. The Gilhooly et al. (2013) study factorially varied incubation activities (verbal – anagram solving vs. spatial – mental rotations), used either a clearly creative verbal divergent task (alternate uses) or a clearly spatial divergent task (mental synthesis) and both divergent tasks were scored for novelty as well as fluency. Significant incubation effects were found, but of most interest were the interactions, in that spatial incubation benefitted verbal divergent thinking more than did verbal incubation activity and verbal incubation activity benefitted spatial divergent thinking more than did spatial incubation activity. These results supported a role for unconscious work during incubation periods in creative thinking tasks and did not support the hypotheses that incubation effects are due to Beneficial Forgetting or attention shifting. The Beneficial Forgetting account predicted the opposite pattern of facilitation (i.e., that similar incubation and target tasks would be more beneficial than different modality incubation and target tasks).

Theoretical Discussion

From recent research discussed above relating to the three main explanations for incubation effects, viz., Unconscious Work, Intermittent Work, and Beneficial Forgetting, it seems that given the effectiveness of Immediate Incubation, in which sets are unlikely to have been developed, the Beneficial Forgetting hypothesis can be ruled out for immediate incubation at least. In addition, Gilhooly et al. (2012 , 2015 ) found no support for the idea of Intermittent Work, from studies in which suitable control conditions were included. Unconscious Work thus remains as the best candidate explanation for the effects of Immediate Incubation periods and it handles the effects of similarity between incubation and target task Gilhooly et al. (2013) . Gilhooly et al. (2013) found that Delayed Incubation was beneficial, but less so than Immediate Incubation in a divergent thinking task (Alternative Uses). It could be that in Delayed Incubation, sets do build up during the initial period of conscious work, and are then reduced by Beneficial Forgetting, after which useful unconscious work could come into play. In contrast, with Immediate Incubation, there are no sets to be overcome and beneficial unconscious work can start sooner than in the Delayed paradigm leading to better performance than with Delayed incubation. Overall, however, the Unconscious Work hypothesis is in contention for both Delayed and Immediate Incubation.

However, the question still arises of what processes might be involved in unconscious work? Could unconscious work processes be identical toe conscious work processes with the sole difference that they are executed without conscious awareness? This issue will now be addressed.

Unconscious Work?

Conscious work is generally rule or strategy governed. Could unconscious work also be rule governed? Poincaré (1910 , p. 329) considered the possibility of a “subliminal self” that worked in the same way as the conscious self, but without consciousness, and might even be a superior “self” since it could find solutions that evaded the conscious mind. Kounios and Beeman (2015) illustrate this notion of a subliminal self by supposing that a man has the job of solving long anagrams during office hours. Suppose the person concerned works systematically all day, on the day shift, from 9 am to 5 pm, trying to solve say, “iaiaeiaeiiamsnrtnmhslbtssdtn,” but when he leaves at 5 pm it is still not solved. Another worker takes over and continues the systematic search on the night shift, from where the first worker left off. At 7 pm the night shift worker phones through to the day shift worker with the answer (cf., insight) saying “It’s “antidisestablishmentarianism!””. In this example, the second shift worker represents the unconscious and works just the same way, using systematic search, as the day shift worker; but, the day shift worker is not aware of the night shift worker’s activities until the answer is phoned through.

To explore further the idea that unconscious work might be a subliminal version of conscious work let us consider conscious processing in the Alternate Uses task. This was addressed in a think aloud study of the Brick Uses task by Gilhooly et al. (2007) in which it was found that participants used strategies, such as scanning the target object’s properties (“Bricks are heavy”) and using the retrieved properties to cue and infer uses from semantic memory (“Heavy objects can hold down things like sheets, rugs, tarpaulin and so on, so a heavy brick could do those things too”). Could unconscious work essentially duplicate this form of conscious work but with no awareness. As we have argued previously ( Gilhooly et al., 2012 , p. 976).

“The standard view in cognitive science is (a) that mental contents vary in activation levels, (b) that above some high activation level mental contents become available to consciousness, (c) that we are conscious of only a limited number of highly activated mental elements at any one time (that is, the contents of working memory) and (d) that strategy or rule based processing, as found in Gilhooly et al.’s (2012) think aloud study, requires such highly activated (conscious) material as inputs and generates highly activated (conscious) outputs.”

On the standard view then, conscious work requires the highly activated contents of working memory and highly activated material is necessarily in consciousness. Overall, it seems impossible that unconscious processes could really be exactly like conscious processes in every respect except that of being conscious. For example, using the rules of arithmetic and temporary working memory storage processes to multiply two 3 digit numbers (e.g., 364 × 279 = ?) is surely impossible without highly activated representations in working memory of the numbers, goals, and intermediate results. The short term representations involved in mental arithmetic would seem to be necessarily conscious. It seems impossible to carry out unconscious multiplication of two or three digit numbers. (With practice of course, one can learn and store three digit multiplication results in long term memory which can be directly retrieved by a type of unconscious process. However, this t is not mental multiplication). Poincaré (1910 , p. 334) made a very similar point when he wrote “It never happens that the unconscious work gives us the result of a somewhat long calculation all made , where we only have to apply fixed rules.” In conclusion, the idea that unconscious work or thought processes could be just the same as conscious work processes with the sole difference that they lack awareness of any mental content, seems unlikely.

However, a challenge to this conclusion has been recently put forward by Hassin (2013) who argues in favor of what he labels a “Yes, It Can” (YIC) principle. According to YIC, unconscious processes can perform the same fundamental, high level functions that conscious processes perform. While it would be generally accepted that the elementary (fundamental?) component processes in carrying out 364 × 279 = ?, are unconscious (e.g., the first step of 364 × 279 is likely to be 9 × 4 = 32, which involves a direct retrieval process that occurs without conscious concomitants in adults practiced in basic multiplication at least) and many such steps and processes are needed, yet precise results need to be held in working memory and precise goals need to be formulated in an organized way (executive processes) all of which seems impossible without mental contents activated to conscious levels. Hassin cites some experiments ( Sklar et al., 2012 ) which appear to show priming in subliminally presented additions and subtractions involving two and even three digits. However, these are far from the long calculations with intermediate results that Poincare discussed as difficult for the subliminal self. Exact calculations cannot realistically be made purely by priming which would activates associatively related numbers and not just the correct ones which are needed at every step of a long calculation if it is to be successful. Similar points apply to all types of problem solving which require multiple steps to be carried out and multiple intermediate results to be held along the way between presentation and solution.

Assuming unconscious work cannot actually be just the same in terms of processing steps as conscious work, of what then, might unconscious work consist?

Poincaré (1910 , p. 333) drew on Epicurus’s (341–270 BC) ancient-world theory of atoms as having hooks so that these elementary building blocks of nature could combine with each other. He imagined ideas like hooked atoms hanging on a wall before relevant ideas/atoms are set in motion during Preparation and continue in motion during Incubation. As with molecules of a gas in a container, the atoms/ideas collide at random and sometimes the hooks snag and a new combination is formed. The atoms initially set in motion can strike atoms at rest and may combine with them. This would represent initial ideas being combined with new ideas so that the products of random combination would always have some relation to the starting conditions of the problem.

Campbell (1960) drew on a range of pre-cursors of his view who had stressed the role of extensive trial-and-error in creative work ( Bain, 1874 ; James, 1880 ) and he was strongly influenced by Poincaré (1910) . Campbell argued that creative problem solving involves a quasi-random generation of associations between mental elements (“Blind Variation”) to produce novel combinations of ideas, some of which may be useful and so be subject to Selective Retention. This approach draws an analogy with biological evolution in which random changes in genetic material lead to changes in organisms, some of which are useful and hence retained by natural selection. Similarly, it is argued that ideas are modified in creative problem solving in ways which are blind to the final solution and only by chance lead ultimately to modifications that solve the problem and are retained for future use. Campbell (1960) quoted extensively from Poincaré’s (1910 ) account of creative thinking in mathematics, as involving extensive quasi-random search, although Campbell did not stress any special role for unconscious processing. His concern was very much with the role of blind trial-and-error, whether carried out at a conscious or an unconscious level. It could be argued that Campbell saw productive conscious creative thinking as like the unconscious work proposed by Poincaré (1910) .

Simonton (1995 , 2003 ) developed Campbell’s ideas and used the notion of “mental elements” which are similar to Poincaré’s (1910 ) “hooked atoms.” However, unlike Campbell, Simonton stresses the role of unconscious processes which lead to new combinations, some of which are retained and selected to enter consciousness on the basis of their “stability.”

In terms of current approaches to cognitive processing, how might novel combinations come about? Parallel spreading activation processes in a semantic network could lead to remote and unusual associations ( Jung-Beeman et al., 2004 ). One specific proposal is that of Helie and Sun’s (2010) Explicit–Implicit Interaction model. In this model, incubation is regarded as involving unconscious, implicit, stochastic associative processes that demand little attentional capacity in contrast with conscious explicit rule governed attentionally demanding processes that run in parallel. In this model, activation spreading through implicit networks during incubation periods leads to novel associations which could facilitate later work when conscious processing resumes and the explicit level processes and knowledge interact with the implicit level processes and knowledge. The model does not seem to deal with incubation leading to a breakthrough of solutions into consciousness without an explicit return to the task. According to Dijksterhuis and Nordgren’s (2006) Unconscious Thought Theory (UTT), unconscious thought, or work, is parallel, bottom-up, inexact, and divergent; whereas conscious thought is, serial, exact, and convergent. Thus, the characteristics of unconscious thought, as envisaged by UTT are consistent with incubation effects.

Overall, there is general agreement among many theorists that unconscious thinking, or unconscious work, in the form of implicit associative processes involving spreading activation [similar to Wallas’s (1926) concept of “associative trains”], is a possible explanation of incubation effects.

How might the suddenness of inspiration be explained? Both Poincaré and Wallas saw this feature of creative thinking as indicative of prolonged unconscious work that found a solution and delivered it to consciousness. However, here Poincaré identified a problem for the unconscious work account. How did the good idea become selected for promotion to consciousness? Poincaré was focussed on mathematical creation and he proposed that in this domain selection was based on the mathematician’s special intuitive sensibility to beauty in mathematics and further that the subliminal self possessed this intuitive sensibility. Poincaré’s theory, as stated in the 1910 paper, is narrow in solely addressing mathematical creation; generalization to other fields, such as poetry, music, physics, and so on, would require specific intuitive sensibilities to be proposed for those fields. An alternative possibility that has general applicability, is that when a problem is set aside, a goal representation remains active for extended time periods, although below the threshold for consciousness. The active goal representation would tend to boost activation flow into associated solution-relevant paths and when a solution combination of associations or a single relevant association became active, the solution and the goal representations would mutually activate each other in a positive feedback loop leading both to become conscious as their activations pass threshold levels. It is suggested that this rising activation (or “rising train of association” as Wallas put it) is experienced as Intimation. The present account has the benefit of automaticity and is parsimonious in not requiring special sensibilities to be invoked. The sub-threshold but active goal representation automatically does the work of selecting promising solution –relevant associations.

Concluding Comments and Limitations

Overall, it can be concluded that the field, although still acknowledging the pioneering work of Poincaré and Wallas, has made considerable progress. The existence of incubation as a beneficial stage in creative thinking has been established through a large number of empirical studies ( Sio and Ormerod, 2009 ), so that the field does not depend on potentially unreliable introspective accounts. New paradigms, such as Immediate Incubation have been established and have helped justify a role for implicit Unconscious Work. Theoretical ideas have been sharpened and refined and the joint effects of spreading activation and subconscious goal activation provide a candidate 9 explanation for insight or intuitive solutions following incubation. The approach put forward here, in terms of spreading activation and goal representations, is most applicable to relatively small scale but knowledge rich problems such as divergent thinking tasks. Further work is needed to develop the present approach for knowledge lean problems, such as laboratory insight problems on the one hand and for larger scale real life problems on the other hand.

Author Contributions

The author confirms being the sole contributor of this work and approved it for publication.

Conflict of Interest Statement

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding. This paper is based on research funded by grants from UK Economic and Social Research Council (RES-000-22-2191) and Leverhulme Trust (F008281G) to KG.

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