Over at Mind Matters, the expert blog I curate at Scientific American, we’re currently featuring a really interesting article by On Amir on the cognitive cost of making decisions:
For instance, it’s long been recognized that strenuous cognitive tasks–such as taking the SAT–can make it harder to focus later on. But recent results suggests that these taxing mental activities may be much broader in scope-and may even involve the very common activity of making choices itself. In a series of experiments and field studies, University of Minnesota psychologist Kathleen Vohs and colleagues repeatedly demonstrate that the mere act of making a selection may deplete executive resources. For example, in one study the researchers found that participants who made more choices in a mall were less likely to persist and do well in solving simple algebra problems. In another task in the same study, students who had to mark preferences about the courses they would take to satisfy their degree requirements were much more likely to procrastinate on preparing for an important test. Instead of studying, these “tired” minds engaged in distracting leisure activities.
Why is making a determination so taxing? Evidence implicates two important components: commitment and tradeoff resolution. The first is predicated on the notion that committing to a given course requires switching from a state of deliberation to one of implementation. In other words, you have to make a transition from thinking about options to actually following through on a decision. This switch, according to Vohs, requires executive resources. In a parallel investigation, Yale University professor Nathan Novemsky and his colleagues suggest that the mere act of resolving tradeoffs may be depleting. For example, in one study, the scientists show that people who had to rate the attractiveness of different options were much less depleted than those who had to actually make choices between the very same options.
Another cool study on this theme comes from Roy Baumeister’s lab at FSU. The experiment began with a large group of undergraduates performing a mentally taxing task, which involved watching a video while ignoring the text of random words that was scrolling by at the bottom of the screen. (It takes conscious effort to not pay attention to such “salient stimuli”.) Then, the researchers offered the students some lemonade. Half of the students were given lemonade made with real sugar, while the other half got lemonade made with a sugar substitute. (The fake sugar tastes sweet but contains no calories.) After giving the glucose time to enter the bloodstream and perfuse the brain – this only takes ten to fifteen minutes – Baumeister had the students make a decision about apartments. It turned out that students given a drink without real sugar were significantly more likely to rely on instinct and intuition when choosing a place to live, even if it led them to choose the wrong place. The reason, according to Baumeister, is that the brains of these students were simply too exhausted to think. They needed a restorative sugar fix, but all they got was Splenda. This research can also help explain why we get “cranky” when we’re hungry and tired: the brain is less able to suppress the negative emotions sparked by small annoyances.
The moral of all this work is that the part of the brain devoted to deliberate analysis and cognitive processing (some circuitry centered in the prefrontal cortex) is remarkably feeble and fragile.