Scarcity: Why Having Too Little Means So Much by Sendhil Mullainathan, Eldar Sharif Page A

evidence have taught us about the way the brain focuses and is disrupted. One common distinction is between “top-down” processing, where the mind is directed by our conscious choice of what to focus on, and “bottom-up” processing, where attention is captured by one stimulus or another in ways that we find hard to control.We saw this in the introduction, when food-related words captured the attention of the hungry. You know the feeling well, from any time a quick movement or sound captured your attention away from what you were doing. A particularly noteworthy form of distraction, one that requires no external distractors at all, is mind wandering. Without our realizing it, the brain’s resting state—the default network—tends to pull us away from what we are doing. True to its name, this happens without our conscious input, when our mind “wanders.” So while we are often able to direct our brain’s activity, at other times we lose that control. For the kids in the school near the trains, the ability to remain focused in the presence of bottom-up distractors depends also on how much work the brain is doing, on how “loaded” it is. Behavioral and neuroimaging studies have shown that distraction along with brain activity related to the presence of distractors increase when the load is high. Top-down attention cannot prevent bottom-up intrusions. When someone says your name across the room at a party, your attention shifts no matter how intently you are trying to focus on something else.
    Scarcity itself also captures attention via a bottom-up process. This is what we mean when we say it is involuntary, happening below conscious control. As a result, scarcity, too—like trains or sudden noises—can pull us away even when we are trying to focus elsewhere.
    An early study tested this idea by giving subjects a simple enough task: push a button when you see a red dot on the screen . Sometimes, just before the dot appeared, another picture would flash on the screen. For nondieters, this picture had no effect on whether people saw the dot. For dieters, in contrast, something interesting happened. They were less likely to see the red dot if they had just seen a picture of food. Flashing a picture of a cake, for example, reduced dieters’ chance of seeing the red dot immediately afterward: it was as if the cake had blinded them. This happened only with pictures of food; nonfood pictures had no effect. Of course the dieters were not physically blinded; they were just mentally distracted. Psychologists call this an
attentional blink.
The food picture, now gone,had made them mentally blink. When the dot appeared, their minds were elsewhere, still thinking about the food. All of this happened in a fraction of a second, too quick to control. Too quick to even be aware of. The title of the study says it best: “All I Saw Was the Cake.”
    The attentional blink occurs briefly. The distracting effects of scarcity, we conjectured, would last significantly longer. To test this, we ran a study with the psychologist Chris Bryan, in which we gave subjects word searches such as this one:
    WORD SEARCH

    Subjects searched for the highlighted word (
STREET
in this case). When they found and clicked it, a new grid appeared and they would look for the next word. A second group of subjects was given the same task but with slightly different words. For example:
    WORD SEARCH

    Theeven-numbered words were the same for both groups. The odd-numbered words were neutral words for the first group but tempting ones for the second:
STREET
became
CAKE
,
PICTURE
became
DONUT
, and so on. We then looked at how long it took participants to find the same words, those they had in common, the even-numbered neutral ones.
    For most subjects, changing the odd-numbered words had no effect. Not so for dieters. Dieters took 30 percent longer to find
CLOUD
after they had just searched for
DONUT
. Dieters were not slow overall—they found
CLOUD
just as