The experiment was done with 58 undergraduates who wore either a white lab coat or street clothes. Those who wore the lab coat made half as many errors on incongruity trials than those who wore regular clothes. In a 2nd experiment, they randomly assigned 74 students to either wear a doctor's coat, wear a painter's coat or see a doctor's coat. They were given tests for sustained attention and those who wore the doctors coat found more differences and had more heightened attention than the other two groups. Further experiments also showed that the students who wore the doctor's coat had improvement in attention.
It appears that certain articles of clothing affect how a person behaves and what "role" they take on. Other experiments show that if you carry a heavy clipboard, you will feel more important. Dr. Adam Galinsky, a professor at the Kellogg School of Management at Northwestern University says that women who dress in a masculine fashion during a job interview are more likely to be hired and a teaching assistant who wears formal clothes is perceived as more intelligent than one who dresses more casually.
I love this experiment. There is an old saying that "clothes make the person". If you dress in old, ill-fitting, shabby clothing it is hard to feel successful and confident. This study points to the idea that it goes further than just wanting to "look nice". Perhaps clothing really does change the psychologic state of the wearer in a way that affects behavior and skill.
(hat tip to Sarah for the article tip)