Science Briefs

The Beautiful Powers of Unconscious Thought

When you're faced with an important decision, people often recommend you "sleep on it." Does science support that belief?

By Ap Dijksterhuis

Ap DijksterhuisAp Dijksterhuis obtained his PhD in 1996 at the Radboud University Nijmegen (at that time still called University of Nijmegen). Between 1996 and 1999 he was a Research Fellow of the Royal Dutch Academy of Arts and Sciences and in 2000 moved to the University of Amsterdam as an Associate professor. In 2002 he became full professor and in 2006 moved back to the Radboud University Nijmegen. In 2005, Ap won both the APA Award for Early Career Contributions and the European Association of Experimental Social Psychology Kurt Lewin Award. In that same year, he also received a Vici grant--the largest grant of the Dutch Science Foundation (NWO)--to fund research on unconscious thought and decision making. In 2007 he published a popular psychology book in Dutch called 'Het slimme onbewuste' ('The smart unconscious') which became a bestseller. Recently, HP/De Tijd selected Ap as one of the top 100 of most influential Dutch people.

"When making a decision of minor importance, I have always found it advantageous to consider all the pros and cons. In vital matters however...the decision should come from the unconscious, from somewhere within ourselves."

Sigmund Freud

When you are facing an important decision, others will sometimes tell you to postpone your decision and "sleep on it" first. In my case it was often my grandmother who gave me this advice. It is a belief many people intuitively share: It helps to put a problem aside for some time in order to arrive at a better decision. Somehow, waiting seems to help us to differentiate between the vital and the futile. Postponing a decision helps us to base our decisions on the appropriate reasons.

But does this "folk belief" hold in a scientific experiment? A few years ago, we conducted an experiment in which we had people choose between four hypothetical apartments. The information was constructed in such a way that one of the four apartments was objectively more desirable than the other three, in that it possessed more positive and fewer negative qualities. However, this was not immediately evident as the apartments were described with a great deal of information. After our experimental participants read all the information about the apartments, they chose their favorite one either immediately or after a period of distraction during which they did some other things. Our hypothesis was that the latter group would continue to "unconsciously think" about the apartments while they were distracted. Indeed, our findings showed that 37 % of the participants who decided immediately chose the appropriate apartment, whereas 60 % of the unconscious thinkers chose the best one (see Dijksterhuis, 2004; Dijksterhuis & Nordgren, 2006). Postponing a decision helps, even if one does not consciously think about it anymore.

The next question was whether unconscious thought could be even more helpful than an equal period of conscious thought. Traditionally, most scholars on decision making have assumed that thorough conscious thought is the best strategy to arrive at sound decisions. This is without doubt sometimes true, but as a general principle it needs to be qualified. We know that under some circumstances (e.g., Wilson & Schooler, 1991), conscious thought deteriorates the quality of decisions. In another experiment we conducted (Bos et al., 2009), our participants chose between six houses that were on sale in our home city, Nijmegen. We simulated the website on which these houses were advertised but removed the asking price. Our participants were given a few minutes time to navigate our "website," and some participants were then given as much time as they wanted to think about the houses, and to further browse through the information. Others were distracted for about 45 minutes (they actually did other experiments) before they decided. Finally, participants chose their favorite house and they were asked to estimate the asking price for each of the six houses based on the information provided. The unconscious thinkers - that is, the ones that were distracted - performed significantly better than the conscious thinkers, a finding that has now been replicated a number of times (see Strick et al., 2009, for a meta-analysis).

In other experiments (Dijksterhuis, Bos, van der Leij & van Baaren, 2009), we asked immediate decision makers, conscious thinkers, and unconscious thinkers to predict the results of soccer matches that were to be played in the near future. The accuracy of the predictions did not differ much for people who didn't know much about soccer. For fans, however, the results did differ. Fans who thought unconsciously made better predictions than fans who thought consciously or fans who guessed immediately. Interestingly, for both immediate decision makers as well as for conscious thinkers, knowledge of soccer did not correlate with the quality of the predictions. Only among unconscious thinkers was this correlation obtained, indicating that the benefits of expertise, at least within the confines of the present paradigm, become apparent when one thinks unconsciously rather than consciously.

Recently, the finding that unconscious thinkers outperform conscious thinkers and immediate decision makers has been replicated in new and interesting domains. Whereas our original experiments were mainly concerned with consumer decisions, it is now established that unconscious thought can improve clinical diagnoses made by clinical psychology students (de Vries et al., 2009), judgments of justice in hypothetical court cases (Ham, van den Bos & van Doorn, in press), and even moral judgments (Ham & van den Bos, in press).

But why is unconscious thought so helpful? In our view, there are two reasons. The first has to do with the different processing capacities of conscious and unconscious processes. Consciousness works in a serial fashion and has a small capacity. That is, it can only do one thing at a time, and it can only work on a very limited amount of information. Unconscious processes have the capacity to work on different things in parallel and can integrate a large amount of information. In a series of experiments, we (Dijksterhuis, Bos, Nordgren & van Baaren, 2006) tested whether the amount of information involved in a decision determines which strategy - conscious thought or unconscious thought - is the most fruitful. In these experiments, experimental participants had to choose their favorite among four hypothetical cars. For some, the cars were only characterized by four attributes, while for other participants the cars were characterized by twelve attributes. Indeed, conscious thinkers fared well when they had to choose among cars described by only four attributes (they actually did a bit better than unconscious thinkers), but they performed very poorly when they had to choose among the cars with twelve attributes. The difference in capacity was also suggested in another experiment (Dijksterhuis, 2004), where we asked conscious and unconscious thinkers who had just chosen between four apartments whether they had based their decision on just one or two attributes or on a more holistic, global judgment. The majority of the conscious thinkers claimed to have followed the first strategy, whereas the unconscious thinkers had done the latter.

We (Dijksterhuis, Bos, Nordgren & van Baaren, 2006) once interviewed people who had recently purchased a consumer product. We asked whether they had thought a lot about it consciously, or whether they had followed the "sleep on it" strategy. As it turned out, buyers of products that only require limited information processing (CD's, clothes, small things such as shampoo), experienced more post-choice satisfaction after conscious rather than unconscious thought, whereas buyers of more complex products (cars, cameras, furniture) experienced more satisfaction after unconscious thought.

The second major reason we offer for why unconscious thought is helpful is that it seems to be better at weighting the relative importance of different attributes. People who judge a house know that a large space as well as many electrical sockets in the kitchen are positive attributes, but they do well to recognize that the first attribute is far more important than the second. Obviously, it should receive more weight in a decision.

The idea that unconscious processes may, at least sometimes, be more effective at weighting than conscious processes is not new. It was already suggested by Freud and more recently by Wilson & Schooler (1991). In their experiments, they showed that conscious thought may actually be detrimental for the weighting process. In our own work, we obtained some suggestive evidence that unconscious thought is effective at weighting. In one experiment (Dijksterhuis & van Olden, 2006), participants had to choose one among five art posters. They did this immediately after seeing the posters, after some time of conscious thought, or after a period of unconscious thought. After they had chosen a poster to take home with them, we also asked participants to what extent they liked each of the five posters. A few weeks later, we called our participants, and asked them how satisfied they were with their choice, to what extent they experienced regret, and for how much money they would be willing to sell their poster. As it turned out, unconscious thinkers were more satisfied and asked for a higher selling price than other participants. Also, the degree to which they liked the chosen poster relative to the ones not chosen correlated with their satisfaction. This was not true for conscious thinkers: The extent to which they liked their poster after choosing it was not predictive of later satisfaction. This strongly suggests they engaged in poor weighting by using the wrong reasons to choose.

Recently, we discovered that unconscious thought leads to an automatic weighting process that continues - at least for a while - as time passes (Dijksterhuis, Bos & van Baaren, 2009). Assume you have to choose between two cars, one with a few very important positive characteristics (good safety record, good mileage) and many unimportant negative characteristics (not many cupholders, only available in three colors), the other with many unimportant positive characteristics (enough cupholders, available in many different colors), and few important negative characteristics (poor safety record, not very good mileage). Most people would choose the former car over the latter, and if you ask people immediately after processing information about such cars, they indeed show a mild preference for the former car. However, after a period of unconscious thought, this preference for the appropriate car has become much stronger. During unconscious thought, important matters become more important, whereas unimportant matters become more unimportant.

Still, unconscious thought is not effective in all tasks. It computes rather rough preferences that allow us to sense that we like one alternative better than another. However, it is not a precision instrument, as it cannot actively use propositional rules such as are needed in arithmetic (try to calculate 26 x 23 without conscious thought - it's impossible). Consciousness, on the other hand, is capable of doing just that--making it more precise. This is relevant for decision making, as it means that when we are faced with a decision that involves little information and not much weighting--that is, a decision for which the weaknesses of conscious thought are not very relevant--conscious thinkers can actually outperform unconscious thinkers. Likewise, when we have to make a decision based on numbers and calculations - such as in games - conscious thought usually outperforms unconscious thought. Payne and colleagues (Payne, Samper, Bettman, & Luce, 2008) provided people with information about various strategies in a game. The various alternatives were based on numerical values (as in returns of stocks) and on probability. In such a case, conscious thinkers are better than unconscious thinkers.

We have learned - especially in the Western world - that conscious deliberation is the holy grail of decision making. This idea needs to be revised. Sometimes conscious thought is more helpful, but sometimes unconscious thought is better. The important avenue for future research is to establish the circumstances when one strategy is better than the other. Perhaps because we have learned that conscious deliberation is almost always good, some people are surprised by, or skeptical about, findings that unconscious thought is helpful, or more generally, that we can perform very useful cognitive operations without conscious guidance. However, our evolutionary history should make clear that it is not surprising at all. Decision making is much older than human consciousness as we know it, and as with all such ancient abilities, we are generally quite good at them if we rely on our unconscious.

Acknowledgement: This research was supported by a Vici grant from the Netherlands Organisation for Scientific Research (NWO) (453-05-004). More information on our research program can be found at


Bos, M. W., Dijksterhuis, A., Bongers, K. C. A., van der Leij, A., Sjoerdsma, A., & van Baaren, R. B. (2009). Complexity and unconscious thought. Manuscript in preparation.

De Vries, M., Holland, R. W., Witteman, C., Vente, F., & Dijksterhuis, A. (2009). Intuitive processes in diagnostic decision-making: Classification after conscious versus unconscious processing. Manuscript under review.

Dijksterhuis, A. (2004). Think different: The merits of unconscious thought in preference development and decision making. Journal of Personality and Social Psychology, 87, 586-598.

Dijksterhuis, A., Bos, M.W., Nordgren, L.F., & van Baaren, R.B. (2006). On making the right choice: The deliberation-without-attention effect. Science, 311, 1005-1007.

Dijksterhuis, A., Bos, M.W., & van Baaren (2009). Unconscious thought leads to automatic weighting. Manuscript under review.

Dijksterhuis, A., Bos, M. W., Van der Leij, A., & van Baaren, R. B. (2009). Predicting soccer matches after unconscious and conscious thought as a function of expertise. Psychological Science, in press.

Dijksterhuis, A., & Nordgren, L.F. (2006). A theory of unconscious thought. Perspectives on Psychological Science, 1, 95-109.

Dijksterhuis, A., & van Olden, Z. (2006). On the benefits of thinking unconsciously: Unconscious thought increases post-choice satisfaction. Journal of Experimental Social Psychology, 42, 627-631.

Ham, J., & Van den Bos, K. (in press). On unconscious morality: The effects of unconscious thinking on moral decision making. Social Cognition.

Ham, J., van den Bos, K. & Van Doorn, E. (in press). Lady Justice thinks unconsciously: Unconscious thought can lead to more accurate justice judgments. Social Cognition.

Payne, J., Samper, A., Bettman, J.R. & Luce, M.F. (2008). Boundary conditions on unconscious thought in complex decision making. Psychological Science, 19, 1118-1123.

Strick, M., Dijksterhuis, A., Bos, M.W., Sjoerdsma, A., Van Baaren, R.B., & Nordgren, L.F. (2009). A meta-analysis on unconscious thought effects. Manuscript in preparation. See

Wilson, T.D. & Schooler, J.W. (1991). Thinking too much: Introspection can reduce the quality of preferences and decisions. Journal of Personality and Social Psychology, 60, 181-192.