How to Hack a First Impression Head high, eyes forward, and please, please keep your hands out of your pockets.

In a study published in 1992, researchers Nalini Ambady and Robert Rosenthal at Harvard University tested the power of first impressions by examining students' perceptions of their professors. For the experiment, Ambady and Rosenthal showed muted, 10-second video clips of professors teaching to participating undergrads, who rated the teachers on 15 dimensions of effectiveness, including warmth, optimism and professionalism, all based entirely on nonverbal cues.

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Ambady and Rosenthal looked at the results and wondered if they could change the ratings by shortening the clips. So they cut them from 10 seconds to five seconds. The ratings didn't change. They cut them to two seconds. Nothing changed. They concluded that we make a snap judgment in the first two seconds of meeting someone, and we rarely adjust it -- even when we get more information. We decide if we like and trust someone before we have even heard him or her speak.