Stimulus factors in the training of prepositional usage in three autistic children.

Language deficient, autistic children were trained to use the prepositions "in" and "on". Three subjects were exposed to conditions of training that differed in the method of employment of stimulus objects used to train prepositional usage. Two subjects were trained first with "ambiguous" stimuli, that is, the same stimulus objects were used for training both prepositions. The two subjects were then switched to a training condition with "non-ambiguous" stimulus objects, that is, objects used for training "in" were different than those used for training "on". The two subjects were then switched to the ambiguous stimulus condition and finally returned again to training with non-ambiguous stimuli (four conditions). A third subject began with training on non-ambiguous stimuli, was switched to an ambiguous condition and was then switched back to non-ambiguous stimuli (three conditions). The results for two of the three subjects indicated that accurate usage of the two prepositions was obtained only under training conditions with non-ambiguous stimuli. Results for the third subject suggested that initial training with non-ambiguous stimuli might enhance subsequent accurate responding with ambiguous stimuli.