THE GENERALIZATION OF EMERGENT RELATIONS IN EQUIVALENCE CLASSES - STIMULUS SUBSTITUTABILITY

After learning the conditional relations AB, BC, and CD, subjects pass ed the emergent relations tests BA, CB, DC, AC, BD, AD, CA, DB, and DA , showing the formation of two 4-member equivalence classes. The A, B, and C stimuli were nonsense syllables; the D stimuli were ''short'' o r ''long'' lines. Generalization of reflexivity, symmetry, and equival ence was assessed by using intermediate line lengths for the training lines in the DD, DC, DB, and DA tests. Test lines closest to a trained line occasioned choice of the same comparisons as those occasioned by the trained line. These test lines, then, functioned as class members . As the disparity between the test and trained lines increased furthe r, the choice of a given comparison decreased systematically. The over lap of the generalization gradients demonstrated the substitutability of stimuli in an equivalence class. The gradients narrowed when subjec ts could indicate that test lines did not belong to either class by th e choice of a ''neither comparison.'' Gradient stability in the absenc e of reinforcement demonstrated the cohesiveness of the classes and th eir generalized extensions. Finally, these results suggest that the co mbined effects of primary generalization and equivalence class formati on can account for the development of naturally occurring and natural kind categories.