The IBM PC keyboard is a convenient response panel for subjects in a reaction time task when the stimuli are presented on the same machine. However, there is a mean delay of about 10 msec and a random error of ±7.5 msec (±5 msec on the AT or PS/2). Our analyses show that for typical single response experimental situations, this added variance is acceptable. With mouse buttons, timing resulted in a delay of 31 ±2 msec if the mouse ball was steady but 45 ±15 msec if it was moving, and a 25-msec refractory period before a second response could be detected. With keys connected to the game port, timing was accurate to 1 msec. For timing the interval between two nearly simultaneous responses, only the game port method is recommended. Any research application should provide an external check on reaction timing accuracy and should correct any mean error. © 1990 Psychonomic Society, Inc.
