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Recent research demonstrated that when autistic children are presented a discrimination task with multiple cues, they typically respond to an abnormally limited number, usually one, of the available cues. This phenomenon, termed "stimulus overselectivity," has been implicated as a possible basis for many of the behavioral deficits characteristic of autism. The present investigation was conducted to systemically analyze the effects of changing the schedules of reinforcement during discrimination training on subsequent stimulus overselectivity. Twelve autistic children were taught a discrimination involving multiple visual cues, with a CRF schedule of reinforcement. The children were then overtrained on either the same (CRF) schedule or on a partial (VR:3) reinforcement schedule. Subsequent overselectivity on single-cue test trials was then assessed. Results suggested that significantly less overselectivity occurred when the children were presented with the VR:3 reinforcement schedule during overtraining. These results are discussed in terms of variables influencing overselectivity and in terms of implications for designing treatment procedures for autistic children.

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Three students with moderate mental retardation were taught a complex stimulus class with a twochoice conditional discrimination procedure applied across eight 10-member stimulus sets. Each set was composed of five age-appropriate and five age-inappropriate examples of clothing, accessories, and leisure items (e.g., a Walkmang radio). Discrimination training was programmed serially across each set, and generalization probes were conducted concurrently among all sets. Generalization probes consisted of unreinforced conditional matching trials with comparison items being drawn from (a) the set undergoing training (within-set probes), (b) sets not undergoing training (between-set probes), and (c) both sample and comparison items from different sets (transitive stimulus control probes). Results indicate that within-set generalization, between-set generalization, and transitive stimulus relations controlled responding by all 3 students for items that had been contingently associated with reinforcement. However, items that gained control of responding through within-set and between-set generalization alone (i.e., not acquired through contingent reinforcement) remained at baseline levels during transitive stimulus control probes. Results are discussed in terms of a taxonomy of multiple sources of stimulus control that underlie socially defined and maintained stimulus classes.

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