Equivalence class establishment, expansion, and modification in preschool children

Preschool children were taught four two-choice match-to-sample conditional discriminations with 10 arbitrary visual stimuli. For 6 participants, 2 of the 10 stimuli served as the sample, or conditional, stimuli in all discrim inations. For 5 additional participants, the same pair of stimuli served as the discriminative, or comparison, stimuli in all discriminations. Equival ence classes were established with more participants in the latter group, r eplicating prior research with participants with retardation. Four particip ants, in whom equivalence classes were established and who were available f or further participation, were exposed to new conditional discriminations w ithout trial-by-trial feedback and involving some novel and some familiar s timuli. Consistent conditional responding was observed, and tests for inclu sion of the novel stimuli in the original classes showed class expansion. T raining to reverse the unreinforced conditional performances produced a rev ersal of class membership in 3 of 4 participants, an outcome not consistent with other studies. The results are discussed with respect to the interact ion of class structure and size.