The Believing Brain - Michael Shermer [146]
Linda is thirty-one years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice and participated in antinuclear demonstrations.
Which is more likely? 1. Linda is a bank teller. 2. Linda is a bank teller and is active in the feminist movement.
When this scenario was presented to subjects, 85 percent chose the second option. Mathematically speaking, this is the wrong choice, because the probability of two events occurring together will always be less than the probability of one occurring by itself. And yet most people get this problem wrong because they fall victim to the representative fallacy, in which the descriptive terms presented in the second option seem more representative of the description of Linda.28
Hundreds of experiments reveal time and again that people make snap decisions under high levels of uncertainty, and they do so by employing these various rules of thumb to shortcut the computational process. For example, policy experts were asked to estimate the probability that the Soviet Union would invade Poland and that the United States would then break off diplomatic relations. Subjects gave this a probability of 4 percent. Meanwhile, another group of policy experts was asked to estimate the probability just that the United States would break off diplomatic relations with the Soviet Union. Although the latter was more likely, these experts gave it a smaller probability of happening. The experimenters concluded that the more detailed two-part scenario seemed more representative of the actors involved.
Inattentional Blindness Bias
Arguably one of the most powerful of the cognitive biases that shape our beliefs is captured in the biblical proverb “There are none so blind as those who will not see.” Psychologists call this inattentional blindness, or the tendency to miss something obvious and general while attending to something special and specific. The now-classic experiment in this bias has subjects watching a one-minute video of two teams of three players each, one team donning white shirts and the other black shirts, as they move about one another in a small room tossing two basketballs back and forth. The assigned task is to count the number of passes made by the white team. Unexpectedly, after thirty-five seconds a gorilla enters the room, walks directly through the farrago of bodies, thumps his chest, and exits nine seconds later.
How could anyone miss a guy in an ape suit? In fact, in this remarkable experiment by psychologists Daniel Simons and Christopher Chabris, 50 percent of subjects did not see the gorilla, even when asked if they noticed anything unusual.29 For many years now I have incorporated the gorilla DVD into my public lectures, asking for a show of hands of those who did not see the gorilla. Out of the more than one hundred thousand people I have shown it to over the years, fewer than half saw the gorilla during the first viewing. (I show the clip a second time with no counting and everyone sees it.) I was able to decrease the figure even more by telling audiences that one gender is more accurate than the other at counting the passes, but I won’t tell them which gender so as not to bias the test. This really makes people sit up and concentrate, causing even more to miss the gorilla.
Most recently, I filmed a special on gullibility for Dateline NBC with the host Chris Hansen, in which we reconstructed a number of classic psychological experiments that demonstrate many of these cognitive biases, one of which was inattentional blindness. Instead of a gorilla, however, we had Chris Hansen himself walk right