Another supportive series of tests were conducted by the University of Chicago. These and many similar tests show how our subconscious computer actually creates the reality for which it is programmed. Three test groups of subjects took part in a mental programming experiment based upon shooting a basketball. All the participating students were tested as to their individual basket-shooting ability and the results were tabulated.I was taught "mental practicing" when I was a music student. This stuff actually works!
Group one was told, “Don’t play any basketball for a month. In fact, just forget about basketball for the entire month.” Group Two was told, “You are each to practice shooting baskets for one full hour a day, everyday, for the month.” Group Three was told, “You are to spend one hour a day imagining you are successfully shooting baskets. Do this each day for the month. Fantasize yourself at being successful shooting baskets. See every detail of your accomplishments in your mind.”
One month later, the three groups were again tested as to their basket-shooting ability. The Group One participants, who hadn’t played basketball for a month, tested exactly the same as they did the first time. Group Two, who had been practicing a full hour every day for a month, demonstrated a 24-percent improvement in their basket-shooting ability. Group Three, who had only imagined that they were successfully shooting baskets for an hour each day, tested 23 percent improved in their actual basket-shooting ability—only one percentage point less than the group that had actually been practicing.
(I found it here, by the way.)