They found that people who were told to sit up straight were more likely to believe thoughts they wrote down while in that posture concerning whether they were qualified for a job while those who were slumped over their desks were less likely to accept written-down feelings about their own qualifications.
The results are an indication that our body posture can affect not only what others think about us, but also how we think about ourselves, said Richard Petty, co-author of the study and professor of psychology at Ohio State.
The study included 71 students at Ohio State. When they entered the lab for the experiment, the participants were told they would be taking part in two separate studies at the same time, one organized by the business school and one by the arts school.
They were told the arts study was examining factors contributing to people's acting abilities, in this case, the ability to maintain a specific posture while engaging in other activities. They were seated at a computer terminal and instructed to either "sit up straight" and "push out [their] chest]" or "sit slouched forward" with their "face looking at [their] knees."
While in one of these positions, students participated in the business study, which supposedly investigated factors contributing to job satisfaction and professional performance.
While holding their posture, students listed either three positive or three negative personal traits relating to future professional performance on the job.
After completing this task, the students took a survey in which they rated themselves on how well they would do as a future professional employee. How the students rated themselves as future professionals depended on which posture they held as they wrote the positive or negative traits.
Students who held the upright, confident posture were much more likely to rate themselves in line with the positive or negative traits they wrote down. In other words, if they wrote positive traits about themselves, they rated themselves more highly, and if they wrote negative traits about themselves, they rated themselves lower.
"Their confident, upright posture gave them more confidence in their own thoughts, whether they were positive or negative," Petty said.
However, students who assumed the slumped over, less confident posture, didn't seem convinced by their own thoughts – their ratings didn't differ much regardless of whether they wrote positive or negative things about themselves.
The end result of this was that when students wrote positive thoughts about themselves, they rated themselves more highly when in the upright than the slouched posture because the upright posture led to confidence in the positive thoughts. However, when students wrote negative thoughts about themselves, they rated themselves more negatively in the upright than the slouched posture because the upright posture led to more confidence in their negative thoughts.
Petty emphasized that while students were told to sit up straight or to slump down, the researchers did not use the words "confident" or "doubt" in the instructions or gave any indication about how the posture was supposed to make them feel.
In a separate experiment, the researchers repeated the same scenario with a different group of students, but asked them a series of questions afterwards about how they felt during the course of the study.
"These participants didn't report feeling more confident in the upright position than they did in the slouched position, even though those in the upright position did report more confidence in the thoughts they generated," Petty said.
That suggests people's thoughts are influenced by their posture, even though they don't realize that is what's happening.
"People assume their confidence is coming from their own thoughts. They don't realize their posture is affecting how much they believe in what they're thinking," he said. "If they did realize that, posture wouldn't have such an effect."
This research extends a 2003 study by Petty and Briñol which found similar results for head nodding. In that case, people had more confidence in thoughts they generated when they nodded their head up and down compared to when they shook their head from side to side.
However, Petty noted that body posture is a static pose compared to head nodding, and probably more natural and easy to use in day-to-day life.
"Sitting up straight is something you can train yourself to do, and it has psychological benefits – as long as you generally have positive thoughts," he said.
For example, students are often told when taking a multiple-choice test that if they're not absolutely sure of the answer, their first best guess is more often correct.
"If a student is sitting up straight, he may be more likely to believe his first answer. But if he is slumped down, he may change it and end up not performing as well on the test," he said.
Petty conducted the study with Pablo Briñol at the Universidad Autónoma de Madrid in Spain and Benjamin Wagner, a current graduate student at Ohio State. The research appears in the October 2009 issue of the European Journal of Social Psychology.