S+ versus S- fading in teaching visual discriminations to severely mentally handicapped children.

Twenty-seven severely mentally handicapped children in three matched groups were trained on both a complex and a simple visual discrimination task with: (1) prompt fading on S+; (2) prompt fading on S-; or (3) no prompting (trial-and-error training). On the complex discrimination task, differences between groups were obscured by a floor effect. Only one subject from each group acquired the discrimination. However, on the simple discrimination task all nine S+ fading, eight S- fading and six trial-and-error training subjects attained criterion. Both S+ and S- fading groups made significantly fewer errors than the trial-and-error group but did not differ significantly from each other. Sixteen children who failed to acquire the complex discrimination in Experiment 1 also participated in Experiment 2. Subjects received additional training on the task by one of four procedures. Neither continued trial-and-error training, continued S+ or S- fading, reversals of the prompt between S+ and S-, or intensity fading resulted in acquisition of the task. Results are discussed in terms of overshadowing and task difficulty.