How is RFT different from stimulus equivalence?

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I often hear behavior analysts comment that RFT is essentially the same thing as stimulus equivalence, or that RFT does not add anything new to the equivalence literature.

Here are a few points to help clarify the difference between RFT and stimulus equivalence:

1) Stimulus equivalence is an empirical phenomenon; RFT is a behavioral theory about how that phenomenon (and other phenomena) comes about. In other words, RFT provides an operant analysis of how/why people are able to form equivalence classes. I cringe when I hear behavior analysts try to use stimulus equivalence as an explanation for some other behavioral event without recognizing that equivalence itself is a behavioral event that requires a technical analysis! This is especially true because the phenomenon of equivalence doesn't readily make sense from a direct contingency analysis (i.e., the "derived" or "emergent" relations are interesting because they're somewhat unexpected based on the organism's history of reinforcement in the presence of the "equivalent" stimuli...that is why we call the relations "derived" or "emergent").

2) Murray Sidman, a pioneer in behavior analysis and stimulus equivalence research, provided some of the earliest behavioral accounts of stimulus equivalence. Sidman's approach, however, was/is primarily a descriptive one: "My own theorizing has been directed not so much at an explanation of equivalence relations but rather, at the formulation of a descriptive system -- a consistent, coherent, and parsimonious way of defining and talking about the observed phenomena" (Sidman, 1994). A precise, coherent description of an empirical phenomenon is important, but it is not the same as a functional, behavioral explanation. RFT attempts to offer such an explanation.

3) In my view, RFT is a more scientifically conservative way to account for equivalence (as compared to Sidman's approach) because it does not require any new behavioral principles at the level of process (in Chapter 2 of the RFT book, we do propose a new behavioral principle at the level of outcome, but that is simply due to the unusual effects we see from the transformation of stimulus functions). Sidman, on the other hand, suggests that equivalence is probably a basic stimulus function "not derivable from more fundamental processes." RFT claims that it IS derivable from more fundamental processes -- basically, a history of multiple-exemplar training and differential reinforcement forrelational responding.

4) The terms RFT uses to describe equivalence and other derived stimulus relations (e.g., mutual entailment, combinatorial entailment, transformation of stimulus functions) are more general than the terms used by Sidman (e.g., reflexivity, symmetry, transitivity, etc.). RFT introduced these new terms so that we could have a language to talk about all different types of stimulus relations (bigger than, before-after, opposites, darker than, etc.). Sidman's terms were taken from mathematical set theory and apply to equivalence relations, but do not work for other types of stimulus relations. In other words, RFT folks did not create new terms just for the hell of it or just because they sounded kewl.

5) RFT, as suggested in point 4, also emphasizes research on types of derived stimulus relations other than equivalence. This is important because stimulus functions can be changed on the basis of these derived relations, and the functions will be changed differently based on different relations. It has been demonstrated many times now that stimulus functions can transfer between members of an equivalence class (i.e., if one stimulus becomes a conditioned reinforcer, other stimuli in the equivalence class may also become reinforcers). But it has also been demonstrated that a stimulus can acquire new functions on the basis of a derived relation other than equivalence to another stimulus. For example, if stimulus A is a conditioned reinforcer and the learner derives a relation of opposition between stimulus A and B, stimulus B is likely to acquire aversive functions (the stimulus functions are transformed on the basis of its derived relation to stimulus A). This has been demonstrated with quite a few different types of stimulus functions and with quite a few different types of relations. Many researchers studying derived relations focus on equivalence relations exclusively, but RFT suggests knowledge of these other types of relations and their impact on the psychological functions of stimuli is also vitally important to a comprehensive theory of language and cognition.



Really nice list.

In the context of a comparison with stimulus equivalence it is good to note that RFT is a theory of how stimulus equivalence comes about, but it would be worth adding that this is only a small part of what RFT is about. The initial excitement about stimulus equivalence was because of its language connection (e.g., maybe this is a model of word meaning; you can train vocabulary using these procedures, etc), but few stimulus equivalence researchers seem focused there anymore.

There is a good reason. As you begin to work with the concept you see that it is rarely possible to "explain" even a normal sentence of any complexity simply by equivalence. Furthermore, as you point out nicely Eric, it is a violation of behavioral thinking to explain one behavioral outcome by appealing to another. Behavioral psychologists don't always notice that, but they do notice it when you try to use it in the clinical or classroom -- stimulus equivalence just tells you little about how to get verbal phenomena to occur if they do not occur naturally. So the scope, precision, and utility of the analysis is inadequate when you try to use stimulus equivalence to unpack even very simple verbal phenomena, nevermind the kinds of things RFT is now leading to actual empirical work on such things as deictic frames, analogy, metaphor, intelligent behavior, and so on.

RFT and stimulus equivalence research, though they overlap, just have really different objectives. RFT is oriented toward a comprehensive behavioral account of language and cognition. I don't hear anyone saying that about stimulus equivalence. After 30 years of work on it, it is pretty obvious that it is not leading there. Quite the opposite. Sidman, 1972 is all about language training. Sidman, 2000 never mentions language at all.

Steven C. Hayes, University of Nevada

Thanks for the multiple exemplar!

Thanks for this explanation Eric, it is "kewl"! Speaking as a layperson who works with persons challenged by autism. RFT seems, for me anyhow, to shed light on the last 10 years of my practice. Just this morning, as a parent explained (as she understands it) how it is that her son learns some things and not others, did (some) of the info from chapters one and two seem to coagulate to make sense for me! (not that I "get" the full meal deal yet...) I am grateful and excited at the potential of RFT and the impact it will have on the lives of many!

I Teach Children with Autism and THEY TEACH ME! (Christina Burk)

no prob

No problem, Shelly. That's great that you're digging into the very dense RFT book and starting to see connections to your work! I encourage you (and others) to post such revelations to this site or the RFT/ACT listservs, as I commonly encounter behavior analysts who want to know how RFT relates to their work in early intensive intervention...