The present study examined how the magnitude of time-out duration following incorrect responses affected the ability of adults to learn simple visual discriminations. Sixty-four college students were randomly assigned to one of four groups that received a 0-, 5-, 10-, or 20-s time-out duration after an incorrect response. Each participant completed a simple visual discrimination task by attempting to determine and remember the correct response for each of eight different color-shape combinations. The results indicated that timeout was effective at enhancing performance, even when reinforcers for correct responses were used. In addition, the effectiveness was dependent on the duration of the time-out. (Contains 6 figures.)