And the accuracy of a snap judgment always depends on what exactly we're sizing up. Ekman doesn't think we can use a thin slice of behavior to judge, say, if someone is smart enough to be our study partner or generous enough to lend us a bus token. "But we can pretty easily distinguish one emotion from another, particularly if it's on the face for a second or more." Spending more time with a genuine person, he says, won't yield a more accurate sense of that person's emotional state.

First impressions are not merely hardwired reactions—we are also taught how to judge others, holding our thin slices up to the light of social stereotypes. Brian Nosek, professor of psychology at the University of Virginia, studies the implicit attitudes that enter into our calculations. Just because someone carries an ACLU membership card or makes a point to invite their senior-citizen friends to dance-club outings doesn't mean they don't have prejudices bubbling under the surface. Nosek and colleagues administer a quick online test that reveals the beliefs people either can't or won't report.

Called the Implicit Association Test, it asks participants to pair concepts, such as "young" with "good," or "elderly" with "good." If, in some part of his mind, "old" is more closely related to "bad" than to "good," the test taker will respond more quickly to the first pairing of words than to the second. In versions of these tests, small differences in response times are used to determine if someone is biased toward youth over the elderly, African-Americans over Caucasians or for President Bush over President Kennedy. "When I took the test," says Nosek, "I showed a bias toward whites. I was shocked. We call it unconsciousness-raising, in contrast to the consciousness-raising of the 1960s."

As subtle as implicit attitudes are, they can cause serious real-world damage. If an angry person stumbles upon someone of a different race or religion, he is likely to perceive that person negatively, according to research. Anger incites instinctive prejudiced responses toward "outsiders," a finding that has important implications for people in law enforcement and security.

Certain physical features consistently prompt our brains to take first-impression Polaroids with a distorting filter. People who have a "baby face," characterized by a round shape, large eyes and small nose and chin, give off the impression of trustworthiness and naiveté—on average, a false assumption. A pretty face also leads us astray: Our tendency is to perceive beautiful people as healthier and just plain better than others.

Leslie Zebrowitz, professor of psychology at Brandeis University in Massachusetts, argues that we overgeneralize in the presence of baby mugs and homely visages. Humans are hardwired to recognize a baby as an innocent, weak creature who requires protection. By the same token, mating with someone who is severely deformed, and thereby unattractive, may keep your DNA from spreading far and wide. But we overgeneralize these potentially helpful built-in responses, coddling adults with babyish miens who in fact don't need our care and shunning unattractive people who may not meet our standards of beauty but certainly don't pose an imminent threat to our gene pool.

Zebrowitz has found that many baby-faced grown-ups, particularly young men, overcompensate for misperceptions by cultivating tougher-than-average personalities in an attempt to ward off cheek-pinching aunts. Think of the sweet-faced rapper Eminem, who never cracks a smile, or the supermodel-juggling, hard-partying actor Leonardo DiCaprio.

Not every observer is equally likely to draw unwarranted conclusions about a smooth-cheeked man or a woman with stunning, symmetrical features. People who spend time cultivating relationships are more likely to make accurate snap judgments.

"A good judge of personality isn't just someone who is smarter—it's someone who gets out and spends time with people," says David Funder, a professor of psychology at the University of California at Riverside, who believes in the overall accuracy of snap judgments. Funder has found that two observers often reach a consensus about a third person, and the assessments are accurate in that they match the third person's assessment of himself. "We're often fooled, of course, but we're more often right."

On the other side of the equation, some people are simpler to capture at first glance than others. "The people who are easiest to judge are the most mentally healthy," says Randy Colvin, associate professor of psychology at Northeastern University in Boston. "With mentally healthy individuals," Colvin theorizes, "exterior behavior mimics their internal views of themselves. What you see is what you get."

Article Courtesy of www.psychologytoday.com