Feeling hungry? Better let your subconscious make the decisions

For optimal decision making, some studies have suggested it's best not to think too hard, that it's advantageous to let your subconscious do the creative heavy lifting. However, other studies have failed to find that unconscious thought leads to superior decisions. To begin solving this contradiction, Maarten Bos and his team have investigated one factor that could make a difference to the effectiveness of unconscious thought – a person's sugar levels. Their rationale is that conscious thought may require high levels of sugar, whereas unconscious thought might be able to operate effectively on low energy.

One hundred and fifty-six students (35 men) abstained from food and drink (except water) for three hours prior to the study. On arrival half of them enjoyed a can of the sugary drink 7-up. The others had a sweet tasting, sugar-free drink. To allow the sugar to reach the brains of those who had 7-up, all the students then watched a nine-minute wildlife film.

Next the students were presented with details about either four cars or four jobs. The items differed on 12 key aspects, which made them either more or less appealing. Whether viewing cars or jobs, there was always one optimal choice that ticked 75 per cent of the boxes; two choices that ticked half the boxes; and one choice that ticked just 25 per cent of the choices.

Finally, half the participants in each drink group then spent four minutes thinking about the jobs or cars before rating the four options in terms of preference – this was the conscious thought condition. The other half of the participants watched a second wildlife film for the same duration of time (to prevent conscious thought about the cars or jobs) before rating the various options – this was the unconscious thought condition.

For the participants with low sugar, their ratings were more astute if they were in the unconscious thought condition, distracted by the second nature film. By contrast, the participants who'd had the benefit of the sugar hit showed more astute ratings if they were in the conscious thought condition and had had the chance to think deliberately for four minutes. "We found that when we have enough energy, conscious deliberation enables us to make good decisions," the researchers said. "The unconscious on the other hand seems to operate fine with low energy."

The study has some shortcomings as the researchers acknowledged. For example, the decision-making was artificial – the participants weren't really choosing a car or job; they were merely rating the various choices in a contrived task. Another thing is that it's far from certain that the participants who watched the second nature film weren't thinking about the cars or jobs at the same time. Nonetheless, the researchers concluded: "Our data show that when we are low on energy we can employ another decision strategy than thinking consciously: we can trust our unconscious."

Further reading

Bos, M., Dijksterhuis, A., and van Baaren, R. (2012). Food for Thought? Trust Your Unconscious When Energy Is Low. Journal of Neuroscience, Psychology, and Economics DOI: 10.1037/a0027388