While trying to look intelligent, a lot of people do things that make them look dumb. 

For instance, people use big words or put on a poker face—tactics that can backfire for some, studies show.

A growing amount of research is teasing out how people form first impressions of others’ intelligence—and how well it works when you try to manage those impressions. The cues people look for in assessing each other’s intelligence are simple. But they aren’t always easy to pull off under pressure. They include showing self-confidence, speaking clearly and smoothly, and responding thoughtfully to what others are saying, research shows.

And put away that phone: One of the strongest and most accurate signs of intelligence is looking at others when you are speaking to them, says Nora A. Murphy, an associate professor of psychology at Loyola Marymount University in Los Angeles, who has conducted six studies on the topic. In one, Dr. Murphy compared, in the same study, the behaviors people adopt when trying to look smart with the cues observers use in sizing up others’ intelligence.

In a 2007 study of 182 graduate students, some participants were instructed to try to appear intelligent during a videotaped discussion with a partner. Each also took an IQ test. Other people were asked to watch the videos and make a judgment about the participants’ likely IQ. Separately, researchers watched the videos for 28 different behaviors.

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