A pedestrian holding a map approaches you and asks for directions. You engage in a short conversation, which is briefly interrupted when two workers walk between you carrying a door. A second later, you continue your conversation.
What you don't notice is that the pedestrian is now someone else. Yep, that's right: A different person took his place when the door passed between you. And you didn't even notice. In fact, fully 50% of people who participated in this 1998 experiment by psychologist Daniel Simons were blind to the switch.
Why did so many people fail to notice such an obvious change? Because we see what we expect to see, and we don't expect to see people we're chatting with morph suddenly into other people. The "default assumption" is that they stay the same.
It's like that old riddle about the man who drives his son to a baseball game, and the car gets stuck on the railroad tracks. A train comes, the father is killed but the child survives, though in critical condition. When paramedics get him to the hospital, the doctor says: "I can't operate on this boy; he's my son."
To this day, people come up with explanations such as alien abduction to solve the "who's the doctor" riddle rather than simply recognizing that it's the boy's mother. The default assumption says doctors are men.
Default assumptions are great fodder for fooling people, a type of illusion that catches the brain in the act of jumping to conclusions. But they also can have serious consequences, from derailing careers in science to putting innocents on death row.
For example, a recent study out of Yale revealed that identical applications for a laboratory job were judged quite differently depending on whether the applicant was male or female. The mythical "John" received substantially more offers — and more money — than the mythical "Jennifer." A report several years ago from the National Science Foundation found a similar pattern: In order to be judged as productive as similar male applicants, female post-docs had to publish an average of three more papers in prestigious journals or 20 more in less-known publications.
Our default assumptions tell us that scientists are men, so that's what we're primed for. And we don't even know we're doing it.
Try this experiment: Quickly picture in your mind's eye a doctor, an airline pilot, a CEO, a hedge fund manager, a newspaper editor, an engineer. Most people's mental picture will quickly register tall white men. If we're in charge of filling one of these jobs, we're usually unaware of what our brains have already decided. A short black woman, a fat person or someone in a wheelchair is highly unlikely to be chosen.
Even if you know a short black female CEO or a guy in a wheelchair who's a physicist, you probably won't revise your default assumption. You'll consider these cases "exceptions."
The same insidious assumptions explain in part why blacks are more than twice as likely to be sent to death row than whites, even when the evidence is equally compelling, and especially if the jury is all white. Even more telling, the blacker the suspect's skin and the more stereotypically African his features, the more likely he is to be judged to be what Stanford psychologist Jennifer Eberhardt called "deathworthy."
Perhaps the most remarkable finding from the "switched pedestrian" experiment was that people had a much harder time distinguishing switches when the person asking for directions was different from themselves — in other words, students had a harder time telling the difference between two middle-aged academics than they did people of their own age group; when the pedestrian was dressed as a construction worker, the perceived class difference made him harder to distinguish. We really do see "them" as "all looking alike."
Having default assumptions doesn't make us bad, just human. We can't get rid of them entirely. But we can recognize how they skew our judgment and take steps to mitigate the problem and even correct for it, just as you correct when you know your car pulls to the right.
For example, we can replace names with initials on job applications, make sure juries are diverse and have sufficient numbers of role models for minority groups in fields such as science to work against a tendency to see them as exceptions. As black, Latino or female scientists become a more normal part of the landscape, default assumptions lose power.
That kind of change won't help anyone outwit the sneaky experimenter who wants to play mind games with you by switching people under your nose. But it could help us outwit our own default assumptions in cases where it matters so much more.
K.C. Cole is a professor of journalism at USC and a former science writer at The Times. kccole.com.