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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-tovariant
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.