Sequence learning in individuals with behavioural limitations.

The production of sequences by two mentally retarded adults and a normally capable preschooler was assessed after each was trained to touch five physically dissimilar and nonrepresentative forms in an experimenter-specified order (denoted A1-->A2-->A3-->A4-->A5). Performance on the 10 constituent two-term sequences was examined (e.g. A-->A2, A2-->A3, A1-->A3 and A2-->A4). The probe data were largely consistent with the five-term sequence performance trained explicitly and suggest the formation of stimulus relations based on relative position rather than a rote stimulus-response chain. The procedures and results were replicated with a second five-term sequence (B1-->B2-->B3-->B4-->B5). The subjects' performances were also assessed on trials in which mixtures of the two sets of stimuli were presented as either two-term probes (e.g. A2-->B4 and B2-->A4; with all three subjects) or five-term probes (e.g. A1-->B2-->A3-->B4-->A5; with the two adult subjects). Again, the subjects' performances were consistent with their baseline training. The mixed-probe data extend prior research on sequence production and suggest the formation of classes of mutually substitutable sequence stimuli. The overall findings highlight the importance of experiential variables in the formation of ordinal relations in developmentally limited individuals.