The present study involved three motor learning experiments; Experiments 1 and 2 measured regulating grasping power and isometric elbow flexion power, respectively. Knowledge of Results (KR) was given after completion of a task of short duration. Experiment 3 was similar to Experiment 2, but procedurally, KR was given concurrently with the task. Accordingly, KR processing takes place within the intertrial interval and parallel to taking task in Experiments 2 and 3, respectively. In these experiments, influences of varying intertrial intervals on the learning process were examined. The results were as follows; 1) In Experiments 1 and 2, shortening of the intertrial interval caused a delay in learning, however this was not the case for Experiment 3. Insufficient KR processing time is considered to be partially responsible for the above delay, 2) In Experiment 3, lengthening of the intertrial interval caused the above delay. These results suggest motor information processing to involve a property of natural decay with the course of time.