The formation of visual stimulus equivalences in children.

Four normal children were presented a series of matching-to-sample tasks, using five sets of visual stimuli designated A, B, C, D, and E. Stimulus equivalences were established by matching stimuli from one set to those from another set. Each set consisted of three stimuli, so matching set A to set D meant that each stimulus in set A served as a sample with all three stimuli in set D as comparisons. Subjects were first taught AD and DC matching and were then able to perform AC/CA matching without additional training. After ED was taught directly, CE/EC and AE/EA performances emerged. Following CB training, three new equivalences were demonstrated: AB/BA, EB/BE, and DB/BD. Oral naming of each stimulus showed that subjects had not assigned a common label to stimuli in the same class, indicating that naming is not necessary for the formation of stimulus equivalences. The absence of response mediation suggests that matching to sample can form direct stimulus-stimulus associations. The data also provide support for the notion that generative performances are outcomes of existing stimulus-control relationships.