Academic journal article The Psychological Record

Reversal Learning Set and Functional Equivalence in Children with and without Autism

Academic journal article The Psychological Record

Reversal Learning Set and Functional Equivalence in Children with and without Autism

Article excerpt

The capability of behaving organisms to respond to physically dissimilar stimuli as if they are the same has been of considerable interest to researchers who study both human and nonhuman beings from various theoretical and methodological perspectives (e.g., human and nonhuman cognitive psychology, Pavlovian conditioning, and behavior analysis). In recent years, one focus of interest has been the phenomenon of stimulus equivalence as defined by Sidman and Tailby (1982). According to their set theory definition, stimuli are said to be equivalent if the individual's behavior toward them exhibits the relational properties of reflexivity, symmetry, and transitivity--typically as exhibited in emergent stimulus-stimulus relations in conditional matching-to-sample procedures. The emergence of new relations without explicit discrimination training, combined with the formal relationship to mathematical equivalence, constitutes the principal argument that stimulus equivalence is the foundation for true symbolic matching to sample.

Vaughan (1988), building on an earlier suggestion by Lea (1984), used another set-theoretic definition that led to a different method for establishing and verifying functional stimulus equivalence. Vaughan used the concept of the partition: division of a given set into two smaller subsets. Each member of each subset is defined mathematically as equivalent to the other member or members of the subset containing that member, if the union of the two subsets is equal to the universe and if the intersection between the two subsets corresponds to a blank set. In Vaughan's implementation, a set of 40 stimuli was divided arbitrarily into two nonintersecting subsets through the establishment of stimuli of one subset as positive (20 S+) and those of the other as negative (20 S-) in a successive (i.e., go, no-go) discrimination procedure with pigeons. When the pigeons mastered the 20 S+ versus 20 S- problems, the discriminative functions of the subsets were abruptly reversed. Originally positive stimuli became negative, and vice versa. When this discrimination reversal problem was mastered, the contingencies were re-reversed, thus reinstating the original discrimination contingencies. Such reversals were programmed many more times over the 2-year course of the study.

Used in this manner, the repeated-reversal procedure allows one to ascertain (1) whether subjects become more efficient in mastering reversed contingencies as training progresses (often termed "reversal learning set") and (2) whether spontaneous discrimination function reversals are observed, that is, if experiencing the consequences of the reversed contingencies with some members of a subset leads to spontaneous discriminative function reversals with other members without explicit discrimination training. The second of these outcomes--demonstrated and emphasized in Vaughan's study--indicates the formation of functional stimulus classes, one way of demonstrating functional equivalence.

Since Vaughan's pioneering study, the contingency-reversal procedures have been replicated with verbally able adolescents and adults (McIlvane, Dube, Kledaras, Iennaco, & Stoddard, 1990; Sidman, Wynne, Maguire, & Barnes, 1989) and with sea lions having extensive conditional discrimination training histories (Kastak, Schusterman, & Kastak, 2001). Findings have often been positive. Very little is known, however, about the conditions under which functional stimulus classes established in this manner can be demonstrated in the absence of verbal ability or an extensive history of intraexperimental discrimination training.

Also yet to be established is the relationship, if any, between reversal learning set and functional equivalence. It seems possible that establishing the behavioral prerequisites for reversal learning set might promote positive outcomes on tests for functional equivalence. Indeed, the spontaneous reversals observed in contingency reversal experiments could be viewed as a logical endpoint of a continuum of reversal learning set effects: maximally efficient behavioral allocation within the concurrent schedules programmed via the reversal learning procedure. …

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