Participants perform the probabilistic reversal learning task either in a testing room seated in front of a computer or lying down while undergoing functional magnetic resonance imaging (FMRI). FMRI is a diagnostic test that uses a strong magnet and radio waves to obtain pictures of brain structure and function. For the scan, the subject lies on a narrow bed with a plastic-encased metal coil close to the head. The bed slides into the scanner - a small tunnel about 6 feet long. All subjects, whether in the testing room or in the MRI scanner, undergo the learning task as follows: