When the participants can perform the dual tasks correctly 90 percent of the time, the movements will be considered automatic, and the subjects will undergo MRI scanning. MRI uses a magnetic field and radio waves to produce images of the brain. For the procedure, the subject lies still on a stretcher that is moved into the scanner (a narrow cylinder containing the magnet). Earplugs are worn to muffle loud noises caused by electrical switching of radio frequency circuits used in the scanning process. The scan will last about 1.5 hours.