The effects of a graduated stimulus change on the acquisition of a simple discrimination in severely retarded boys

Methods were compared for teaching severely retarded boys to discriminate the position of a 0.75-in. black square and to press the response key closest to it. Seven boys were given trial-and-error training; one learned the task. The six boys who did not learn were presented with a program of graduated stimulus changes. All but one acquired the performance, and he was under appropriate control during the program. When he reached the criterion stimuli, he reverted to a position-based response learned during trial-and-error training. Six similar subjects were presented with graduated stimulus training alone. All six learned the criterion discrimination with few or no errors. Both groups were tested for retention of the criterion performance 35 days after training was completed. Two boys who had near-perfect criterion discrimination performances showed no signs of retention after 35 days. These boys had a history of trial-and-error training.