The "unconscious thought" theory for making complex decisions was proposed in a 2006 study by Ap Dijksterhuis at the University of Amsterdam in the Netherlands, and colleagues.
The team showed volunteers a series of cars and their attributes on a screen, before asking half of them to think carefully about choosing the best car, and the other half to solve anagrams - a distraction technique to allow unconscious processing.
Those in the anagram group were more likely to choose the cars with the best attributes, leading the researchers to conclude that it is best to leave tough choices to the unconscious (Science, vol 311, p 1005).
Now two teams have questioned this conclusion. Instead, they suggest that the volunteers made their decisions when they first viewed the data, based on an immediate gut instinct. Those in the anagram group simply recalled this original decision when asked to choose.
Those in the "thinking" group, however, reconsidered their first impressions while the details of the cars faded from their memory, which led to poorer choices.
"What Dijksterhuis ignored is that people might already decide when they first hear about the cars, and not after thinking about it or solving anagrams," says psychologist Daniel Lassiter of Ohio University in Athens.
To test this hypothesis, Lassiter and his colleagues repeated Dijksterhuis's experiment with a twist: they told the volunteers to memorise the cars' attributes while viewing them, thus distracting their attention from making an immediate decision.
The small tweak made a big difference. In contrast to Dijksterhuis's experiment, students made better choices when they spent time thinking, rather than solving anagrams (Psychological Science, vol 20, p 671).
Lassiter says this is strong evidence against the idea that unconscious deliberation is superior to conscious decision-making. He questions whether unconscious thought exists at all.
This is evidence against the idea that unconscious deliberation is superior to conscious decision-making Axel Cleeremans from the Free University of Brussels (ULB) in Belgium carried out a very similar experiment to Lassiter, but using apartments instead of cars, and came to the same conclusion.
He also asked another set of volunteers to choose as soon as they had viewed the apartment information, with no time for any deliberation. The decisions made were of the same quality as those made by the volunteers he asked to solve anagrams, Cleeremans says.
This is further evidence that unconscious thought does not improve decision quality. He presented his findings at the annual meeting of the Association for the Scientific Study of Consciousness in Berlin, Germany.
Dijksterhuis maintains that unconscious thought exists. He says that he has carried out further experiments directly comparing decisions formed after a period of unconscious thought with those based on first impressions only, and found the former to be superior. He intends to submit these for publication.
John-Dylan Haynes of the Bernstein Center for Computational Neuroscience in Berlin says that the new results show that unconscious thought during anagram solving had no great effect on decision quality. But he says that unconscious processing could be important for gut reactions.