Abstract
Two subjects with retardation who exhibited generalized identity matching, but who had extensive histories of failure to acquire arbitrary matching, were exposed to a series of conditions designed to train separately the components of a two-choice conditional discrimination. First, the successive discrimination between the sample stimuli was established by programming a different schedule of reinforcement in the presence of each sample stimulus. Schedule performance was acquired and maintained by both subjects, but neither acquired arbitrary matching. To train the simultaneous discrimination between the comparison stimuli, 1 subject was then exposed to a series of simple discrimination reversals and subsequently failed to acquire arbitrary matching. Both subjects acquired arbitrary matching under a procedure that maintained both the sample and the comparison discrimination by first presenting entire sessions composed of one sample-comparison relation and then gradually reducing the number of consecutive trials with the same sample until sample presentation was randomized (schedule performance was maintained). Removal of the schedule requirement had no effect on arbitrary matching accuracy. Both subjects subsequently demonstrated control by relations symmetric to the trained relations.