Study: Nodding or Shaking Head Changes Opinion

— It goes without saying that the people who read this column are all rational folks who reach conclusions based entirely on the evidence and they can't be influenced by such unrelated events as their own body language. There's not a chance, for example, that your convictions are likely to be affected by anything as irrelevant as nodding your head in agreement with someone else's statement, or shaking it back and forth in disagreement.

Don't bet on it, says psychologist Richard Petty of Ohio State University, whose research shows that what we think about something can indeed be influenced by simply nodding or shaking our head.

But Petty's findings are a bit confusing. It turns out that simply nodding yes doesn't necessarily mean we are more likely to agree with whatever we are hearing. It may have just the opposite effect, reaffirming our own opposing views.

Myriad of Influences

And shaking no doesn't necessarily mean we will disagree more with what we are hearing. We may be more inclined to agree with arguments that we would normally oppose.

The findings also reaffirm something else. Old Sigmund was right when he concluded that we are very complex creatures, subject to influence by a vast reservoir of data that we may not even know is there.

"There's so much that goes on at the unconscious level," Petty says. "Freud was right about that. He was wrong about a lot of the details, but he certainly was right in that there's so much going on [in our brains] that we're just not aware of."

Petty's research, which he carried out with former doctoral student Pablo Brinol, now at the Universidad Autonoma de Madrid, began with a study that seemed to reaffirm something psychologists have known for years. When we nod yes, we tend to agree with what we are hearing.

"That has been shown before," Petty says.

The surprise came when a proposal read to the participants was supported by very weak arguments. The effect of the head movements was reversed.

"People who were nodding their heads [in agreement] were actually more negative towards the proposal than people who were shaking their heads side to side," Petty says. So nodding yes made them disagree more than people who were shaking no in disagreement.

That's a little hard to visualize, but hang around for a minute or two.

A Matter of Confidence

To carry out the research Petty had to resort to a little subterfuge, a common practice among psychologists. The researchers told 82 college students who participated in the program that their job was to determine if simple head movements would degrade the sound quality of a new set of stereo headphones.

Half were told to nod their heads up and down once every second, and the others were told to shake their heads back and forth once a second. A recording of a campus radio program was transmitted through the headphones, featuring music and an editorial.

The editorial advocated increasing tuition, a subject that was sure to command the attention of the students. Half the participants heard reasonable arguments in favor of the increase (lower class size, more individual attention, better scholastic performance leading to better jobs) and the others heard really lame reasons for why they should support the increase.

"We told them we only had daffodils on the campus, and we needed the money so we could plant some tulips for variety," Petty says.

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