Have you ever been in doubt about which is the right choice when making a decision? Whether it’s a big one such as what study program to follow, or a seemingly trivial one such as what to wear on a date. Humans are great at contemplating. If you then asked a friend for help, something you have probably heard before is the advice to “sleep on it”. Conventional wisdom suggests that putting a decision aside and sleeping on it helps in finding the right choice. But is this really the case, one might wonder. The answer to this is more complex than a simple yes or no, so let’s start with what actually happens when you are sleeping: unconscious processing.

The capacity of the unconscious

Scientists generally agree on the benefits of unconscious processing – the work that our brain does while we are not conscious of it (yes, our brain does a lot of this). You have probably had the situation before in which you were desperately trying to think of a fact, such as your high-school teacher’s name, but you could just not remember it. And then minutes or hours later you suddenly have the ‘aha-moment’ in which you remember her name totally out of the blue. That was the work of your (dear) unconscious mind. Our conscious processing capacity is very limited, for example, we are not able to concentrate on two things at the same time. Most decisions, however, include a vast amount of information that needs to be integrated and weighed against each other, so the conscious mind might simply not be able to do this due to its limited processing capacity. Hence, taking some time away from the decision and letting the unconscious tackle the problem would appear beneficial.

Conscious versus unconscious decisions

In a study by Bos and colleagues this benefit of unconscious processing was proven. Subjects had to decide which car they would buy based on a description of positive and negative attributes, varying in importance concerning the car purchase. Ideally, the subjects would find the quality cars in the display by weighting the different attributes and finding the important ones while discarding the trivial ones. What they found was that subjects that put the decision aside and were distracted for a couple of minutes not only made objectively better decisions than those who made a decision right away, but also reported to be subjectively more satisfied with their decision. Another study found similar results when comparing groups that either had time to consciously think about the decision or were distracted and thus, subject to unconscious thought. In sum, a period of unconscious thought prior to making a decision is not only superior to instant decision making, but also to a period of conscious thought. So taking some time off the decision is beneficial, but is it even more beneficial to sleep on it as common sense suggests?

Unconscious versus overnight decisions

Scientifically speaking it would also make sense that sleep adds a positive effect, since it generally benefits several cognitive processes, also those related to choice such as memory. A recent study by Karmarkar and colleagues was the first to experimentally investigate whether sleep adds onto the positive effect of putting the decision aside for a while. They compared the choices subjects made concerning laptop satchels, which were presented with different attributes just like in the previous study. This time, however, there was no objective good choice, all satchels had a similar quality. It was simply about how satisfied and confident the subject felt with their subjective, preference-based choice. What they found was that sleep did not improve the subjective decision quality, surprisingly there was a trend indicating that the quality had decreased as compared to the group that had only taken some time away from the decision.

Complex versus minor decisions

Does this mean that sleep is even harmful when trying to make the right decision? Probably not. The experimental design did not reflect the idea behind a real-life decision very well as the subjects were not given the possibility to not choose a laptop satchel at all and the decision was likely not personally relevant to the subjects, making the decision generally not very complex. For now we can clearly state the benefits of leaving a complex decision to rest for a while, as shown in the first studies, and whether sleep adds onto this still needs to be investigated in further experiments. Yet, it appears that this effect does not hold true for minor decisions.

Closing thoughts

So where does this leave us? Should we generally stop trying so hard to consciously find a solution and leave everything to the unconscious? No! Each system has its strong and weak points. After all, your unconscious is likely never going to find out what 119 multiplied by 28 is. Yet, if you are facing a complex problem it is beneficial to let your unconscious mind give it a try. As a rule of thumb, you might consciously compare alternatives for simpler decisions, when weighting of attributes is easy, meaning that your conscious processing capacity is big enough. However, when weighting is hard, it might be useful to form a general first impression and then take some time away from the decision to let the unconscious do the work. Whether sleep is really needed for this or if a period of distraction is equally effective is up to this point rather unclear. Nonetheless, it seems like it is not a good idea to postpone every minor decision to the next day, sorry to all procrastinators!

Bos, M. W., Dijksterhuis, A., & van Baaren, R. B. (2011). The benefit of “sleeping on things”: Unconscious thought leads to automatic weighting. Journal of Consumer Psychology, 21, 4-8.

Dijksterhuis, A. (2004). Think different: The merits of unconscious thought in preference development and decision making. Journal of Personality and Social Psychology, 87(5), 586-598.

Karmarkar, U. R., Shiv, B., & Spencer, R. M. C. (2017). Should you sleep on it? The effects of overnight sleep on subjective preference-based choice. Journal of Behavioral Decision Making, 30(1), 70-79.