Differences in development of visual and auditory-visual equivalence relations.

Five young adult females with mild mental retardation were given match-to-sample training and testing to develop four classes of equivalent stimuli: two classes containing three forms each and two classes containing one spoken nonsense syllable and two forms each. All subjects demonstrated development of all possible equivalence classes involving these stimuli. For 4 of 5 subjects, the classes that included auditory stimuli developed more rapidly than those that did not.