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Nod Your Head if You Agree with Yourself: How Your Own Body Language Can Persuade You

We should learn to decode our own nonverbal signals

Keep your eyes peeled next time you watch a video of a political rally or assembly. You'll often notice that, arranged directly behind the speaker and facing the viewer, is a line of folks who are emphatically bobbing their heads in agreement throughout the speech. They may well be planted there by design. Nonverbal signs of approval like these can act as subtle but powerful cues shaping our own acceptance of the message that's being broadcast.

The impact of nonverbal signals is not lost on the self-helpers, and a whole industry has blossomed to teach us how to interpret someone else's body language or control our own on a date or at a job interview, or how to resist the pull of these signals when they're skillfully deployed by used car salesmen. Much of this advice is decently grounded in proper science.

But I don't see the body language gurus dispensing advice about how to interpret one's own body language. What if we use our own body language to make inferences about our own thoughts? And what if these inferences could shape our attitudes?

These seem like absurd questions—you'd think that our body language would be a reflection of our opinions, rather than a cause of them. It also seems strange to think that we would have to rely on our own body language to figure out what we're thinking. But the growing field of embodied cognition suggests exactly that. It seems that the signals between thinking and moving go both ways, and that what our body is doing can affect our thoughts.

An especially interesting study along these lines was published in 2003 by Pablo Brinol and Richard Petty. They recruited college student participants, telling them that they were working with a manufacturer to conduct a consumer study to test the sound quality of stereo headphones. The students listened to a pre-recorded "radio" program, which was really a carefully constructed script disguised as an editorial giving a number of good arguments as to why students should be required to carry a personal ID card. Half of the subjects were told that they should nod their heads throughout the message in order to test how the headphones performed when people moved their heads. The other half were told to shake their heads left to right while listening to the message. Afterwards, the students answered a slew of questions about the headphones' performance and their attitudes towards the proposed ID cards—the latter, they were told, was necessary because their attitudes might taint their evaluation of the headphones, and this needed to be controlled for.

You might see where this is going: the students who'd nodded their heads throughout the message were more likely to think the ID cards were a good idea. But that's not the whole story. This finding only held when the editorial contained strong arguments. When the arguments were weak, exactly the reverse happened: the head-nodding students now thought the ID cards were a worse idea than the head-shaking subjects.

Why would this be? It seems that the students were using their own head movements as a cue to agreement, all right. But not agreement with the message itself. Rather, argued Brinol and Petty, their body language was used to infer whether they agreed with themselves. The idea is that, when listening to persuasive arguments, people don't just listen passively—they generate an internal dialogue that keeps a running score of whether the arguments are good ones. If they are, they'll tell themselves "Good point." If not, they'll react by internally groaning. The head movements apparently affected how confident people were in these assessments, not how confident they were in the arguments themselves. In other words, the internal dialogue really did act as a dialogue: between the self that evaluated the message, and the head-nodding or head-shaking self that was listening to the evaluation. And the body language served as a cue as to what that listening self was thinking.

Maybe someone should put that in their manual on body language.

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It's not exactly about body language, but Gretchen Rubin has an interesting blog post on behaviors that can act as "tells" revealing our inner state.

To read the original head movement study:

Brinol, P. & Petty, R.E. 2003. Overt head movements and persuasion: A self-validation analysis. Journal of Personality & Social Psychology, 84, 1123-1139.

For an interesting follow-up study involving body posture:

Brinol, P, Petty, R.E. & Wagner, B. 2009. Body posture effects on self-evaluation: A self-validation approach. European Journal of Social Psychology, 39, 1053-1064.