This experiment studies whether the rate of operant discrimination under the control of the time interval schedule of successive presentation of stimuli is constant. Method: The Ss were 19 experimentally naive pigeons maintained by restricted feeding to 80 percent of their ad libitum weight. A modified Skinner box was used. The Pecking of the key operated an electric switch which permitted automatic recording and programming of reinforcements. The key was a disc of translucent glass which was illuminated from outside of the box by a projective lamp through a monochromatic filter and a neutral wedge. After preliminary training for the pecking response, the Ss were trained to discriminate between the positive light stimulus which is to be reinforced and the negative one. A single stimulus was presented successively in random order and three time interval schedules, 7 sec., 15 sec. and 30 sec. were chosen. The number of reinforcement per day was 40 and the criterion of learning was set at 90 percent correct response with no errors for the last half of the series. On the next day after the Ss attained to the criterion of learning, testing the effect of learning was carried out under the extinction trials in one series similar to that of training trials. Results: The rate of acquisition and extinction in the operant discrimination was different for the different time interval schedules. In 15 sec. time interval the Ss learned more rapidly than in the other time intervals. The total number of reinforcements required for the attainment to the criterion of learning was the least in 15 sec. interval, but the difference between 7 sec. interval and 30 sec. interval was not significant. The difference between three time interval schedules in extinction trials was not significant statistically. The 15 sec. interval schedule showed most effective in operant discrimination in this experiment.

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