Stimulus Class Formation in Animals
Thomas R. Zentall Department of Psychology University of Kentucky Lexington, KY 40506-0044 Telephone: 606-257-4076/Fax: 606-323-1979 E-Mail. Zentall@pop.uky.edu
The simplest kind of stimulus class is one defined simply by a common trained response. Other stimulus classes do not require training of each of the members but they derive their membership from the physical similarity among class members through the process of stimulus generalization. Stimulus classes of greater interest are nonsimilarity based classes for which membership implies properties not explicitly experienced, or so-called emergent properties. Nonsimilarity-based or arbitrary classes can develop when two or more arbitrary stimuli become directly associated through their pairing with a common event. These classes appear to develop during matching-to-sample training when two or more samples are associated with the same comparison (i.e., many-to-one matching).
Convergent evidence will be presented for the development of emergent relations between these samples (or for their common coding) in the form of. (1) Transfer: When a subset of these samples is associated with new comparisons there is evidence that the remaining samples are also associated with the new comparisons. (2) Interference/facilitation: When a subset of these samples is associated with new comparisons and a delay is inserted between the samples and new comparisons, interpolation of one of the remaining samples into the delay will interfere with or will facilitate matching accuracy depending on whether the interpolated sample was paired with the same comparison as the current sample in original many-to-one training. (3) Partial versus total reversal: When originally trained sample-comparison associations are reversed, reversals are faster when all of the associations are reversed than when only half of the associations are reversed (and the rest remain relevant). (4). Samples associated with the same comparison are harder to discriminate from each other (in a simple successive discrimination) than are samples associated with different comparisons. (5) The retention functions (matching accuracy as a function of delay inserted between the sample offset and comparison onset) for samples associated with the same comparison are much more similar in slope than those same retention functions when samples are associated with different comparisons.
The relation between this kind of stimulus class formation and formal (Sidman) stimulus equivalence will be discussed. Specifically, direct evidence for the three defining characteristics of stimulus equivalence (reflexivity, symmetry, and transitivity) in animals will be presented. Finally, the relation between stimulus class formation and human language will be addressed.