To conduct their research the asked 80 novice and skilled golfers to practice a putting stroke until they got it right 3 times in a row. They then asked half the golfers to spend 5 minutes describing what they did while others took a break and did something completely unrelated to golf.
What they found was that the golfers who talked about what they were doing took roughly twice as many attempts to repeat the task as the golfers who had been doing something else.
The researchers claim that the loss of performance is due to an effect called “verbal overshadowing” which makes the brain focus more on language centres than on the systems that support the skill in question.
Interestingly, this same effect has been shown to adversely impact the ability of a person to recognise faces. So if the police ask a witness to describe the face and appearance of a suspect before showing them photographs of likely suspects, they will actually reduce the likelihood of them identifying the correct person. Intuitively, you’d think this would be to the other way round.