A methodological integration of generalized equivalence classes, natural categories, and cross-modal perception

A generalized equivalence class contains some stimuli that are perceptually disparate and others that resemble one another. They all function as members of a generalized equivalence class when all of them occasion the selection of the others in the set, and a response trained to one or a few are occasioned by all other stimuli in the set. This article formalizes the structural relations among the stimuli in these classes and identifies the generalization tests needed to fully document the range of stimuli that function as members of such a class. These include tests conducted in variant-to-base, base-to-variant, and variant-to-variant formats. The structural and functional properties that characterize generalized equivalence classes also characterize naturally occurring categories, natural kinds, semantic superordinate categories, and cross-modal perceptual classes. Thus, the procedures used to measure generalized equivalence classes could also be used to document these other classes.