hungerIn his book Thinking Fast and SlowDaniel Kahneman describes the brain as made up of two systems. System 1 is fast, emotional, and almost automatic--I think of this as "intuition." System 2 controls more logical, deliberate processes. There are many factors that can influence which system you use to make a decision (anchoring, availability, substitution, loss aversion, framing, etc.) and Kahneman's book discusses these. But other environmental factors can influence which system takes over. This post discusses how hunger shifts the balance from System 2 to System 1.

First up is a study on Israeli judges' parole decisions broken up by time of day by Shai DanzigeraJonathan Levavb, and Liora Avnaim-Pessoa (edited for PNAS  by Kahneman). Here's the abstract:

Are judicial rulings based solely on laws and facts? Legal formalism holds that judges apply legal reasons to the facts of a case in a rational, mechanical, and deliberative manner. In contrast, legal realists argue that the rational application of legal reasons does not sufficiently explain the decisions of judges and that psychological, political, and social factors influence judicial rulings. We test the common caricature of realism that justice is “what the judge ate for breakfast” in sequential parole decisions made by experienced judges. We record the judges’ two daily food breaks, which result in segmenting the deliberations of the day into three distinct “decision sessions.” We find that the percentage of favorable rulings drops gradually from ≈65% to nearly zero within each decision session and returns abruptly to ≈65% after a break. Our findings suggest that judicial rulings can be swayed by extraneous variables that should have no bearing on legal decisions.

The Economist summarized the paper and produced a graphic with the main takeaway:

israeli-parole-board

The second paper, by Ilona Grunwald-Kadow and coauthors, analyzes the neural behavior of fruit flies when deprived of food (via @tylercowen and @IFLscience). Their results are explained in this press release from the Max Planck Institute:

The results show that the innate flight response to carbon dioxide in fruit flies is controlled by two parallel neural circuits, depending on how satiated the animals are. “If the fly is hungry, it will no longer rely on the ‘direct line’ but will use brain centres to gauge internal and external signals and reach a balanced decision,” explains Grunwald-Kadow. “It is fascinating to see the extent to which metabolic processes and hunger affect the processing systems in the brain,” she adds.

Remember this next time you're trying to decide between working through lunch or grabbing a bite to eat. Do your body and your neighbors a favor by taking a break.

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