on stimulus generalization and stimulus classes

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Journal of Behavioral Education [jbe] ph182-jobe-460873 January 25, 2003 10:33 Style file version Nov 28th, 2002

Journal of Behavioral Education, Vol. 12, No. 1, March 2003 (C© 2003), pp. 77–83

On Stimulus Generalization and Stimulus Classes

Anthony J. Cuvo1

Stimulus generalization has been defined as the spread of effect of reinforcementfor responses emitted in the presence of one stimulus to different stimuli presentedunder extinction conditions. As a result of stimulus generalization, novel stim-uli come to exert stimulus control over members of the response class. Studiesin the applied behavior analysis literature, however, have reported experimentalpreparations that included prompting and reinforcement procedures during whatwere claimed to be stimulus generalization conditions. These studies violated theprocedural requirement that stimulus generalization be tested under extinctionconditions. Responses that come under the control of a class of stimuli may do soby direct training or by stimulus generalization. It is desirable for organisms torespond in the presence of members of an appropriately constructed stimulus class,but we should understand the mechanism of entry into the class by its members. Ifinaccurate claims of stimulus generalization are made when training proceduresare used in the ostensible generalization conditions, the robustness of the orig-inal training procedures will be over estimated. By adhering to the operationalrequirements of behavioral definitions, we could better understand the power andlimits of our educational and training procedures.

KEY WORDS: stimulus generalization; stimulus class; generalization.

The technical terms of an academic discipline play an important role in accu-rate communication among members of the discipline. A common language allowsfor consistent understanding of terms, and facilitates relatively precise exchangeof information among the adherents of a discipline, such as behavioral educa-tion. Furthermore, a standard set of definitions allows for efficient communicationbecause one does not have to operationally define the terms in each discourse;the terms should have, more or less, the same referents for everyone. If there isdrift in the denotation of the terms in written or spoken communication because

1Rehabilitation Institute, Southern Illinois University, Carbondale, Illinois 62901; e-mail:[email protected].

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of inconsistent or inappropriate operationalization of their procedures, that cancreate ambiguity in meaning and confusion in understanding. Even worse, withinappropriate use of technical terms or procedures we may make false claims abouta phenomenon and veer off course in the accuracy of our knowledge base. We maycome to believe that an educational outcome, for example, is either more or lessrobust than it really is. The present manuscript is a cautionary note occasioned bymethodological deviations in the behavioral preparations related to claims of stim-ulus generalization. Illustrations will be cited from education and training researcharticles published in several behavioral journals.

The term stimulus generalization or induction has been defined as “ the spreadof effects of reinforcement (or other operations such as extinction or punishment)during one stimulus to other stimuli differing from the original along one or moredimensions” (Catania, 1998, p. 391). The experimental preparation involves dif-ferentially reinforcing responses in the presence of certain stimuli, and then ob-serving performance under extinction conditions in the presence of other stimulinot present during training (Donahoe & Palmer, 1994; Harrison, 1991; Keller &Schoenfield, 1950; Skinner, 1953). Claims of stimulus generalization can be madeif the target response occurs under those non-training conditions. It is importantto note the procedural difference between responses produced under acquisitiontraining and generalization testing conditions. For the former, responses are ac-quired by differential reinforcement and possibly other forms of training. For thelatter, responses are emitted in the presence of novel stimuli by spread of effectwithout benefit of direct training.

The classic experiment by Guttman and Kalish (1956) from the experimentalanalysis of behavior literature provides a laboratory model for testing stimulus gen-eralization under extinction conditions. In their experiment, pigeons were trainedto peck a key with a green light on a VI 1-minute reinforcement schedule. Af-ter attaining a steady state of responding under this reinforcement condition, thebirds were exposed to keys with green plus 10 other wavelengths of light withoutreinforcement for key pecking. A figure of the key pecking data showed a sym-metrical curve generalization gradient, with fewer responses emitted the more thelight wavelength differed from the one presented during training. In the Guttmanand Kalish experiment, responses were reinforced during training, but not duringgeneralization trials. Research reported in the experimental analysis of behaviorliterature tends to be true to this preparation for the study of stimulus generalization.

In the applied behavior analysis literature, in contrast, there have been incon-sistencies regarding the conditions implemented to test stimulus generalization,and consequently, the evidence needed to support its outcome. In the applied lit-erature claims of stimulus generalization have been made when there have beenreinforcement and other forms of training in the presence of alleged generalizationstimuli. Essentially, direct training in various forms has occurred, and generaliza-tion has been attributed to the performance under some of those trained conditions.

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Generalization and Classes 79

Extinction, therefore, has not been the test condition for claims of stimulus gener-alization by some researchers. This research will be illustrated from several appliedbehavioral journals, and its implications for education and training discussed.

CLAIMS OF STIMULUS GENERALIZATIONWITH REINFORCED RESPONSES

In a number of recent studies, response consequences, typically in the formof differential reinforcement, were provided in what were termed stimulus gener-alization conditions. For example, when teaching microwave skills to adults withmoderate mental retardation, a FR 13 reinforcement schedule was employed forcorrect responses during generalization probes (Jones & Collins, 1997). In anotherstudy, edible reinforcers used during training were discontinued during generaliza-tion tests, but praise for correct as well as attempted sign language was maintained(Dalrymple & Feldman, 1992). In a study designed to teach children with autismto ask questions about hidden objects, training sessions were conducted in thegirls’ bedrooms, and generalization sessions occurred in the living rooms with themothers providing intervention (Williams, Donley, & Keller, 2000). Although themothers never provided prompts, “the contingencies of reinforcement during allgeneralization sessions corresponded to the training sessions that preceded them”(p. 629).

In a study that investigated procedures to teach verbal responses to ques-tions about medication, differential response consequences were provided dur-ing both generalization pre-and posttests (Cromer, Schuster, Collins, & Grisham-Brown, 1998). During the posttest, for example, descriptive praise was providedfor correct responses, and verbal correction as well as response practice were theconsequences for errors. Other studies also reported using the same differentialreinforcement procedures during generalization probes as were employed dur-ing training (Collins, Branson, & Hall, 1995; Fickel, Schuster, & Collins, 1998;Mitchel, Schuster, Collins, & Gassaway, 2000; Sandknop, Schuster, Wolery, &Cross, 1992; Smith, Collins, Schuster, & Kleinert, 1999). Although the prepara-tion of the studies cited above included differential reinforcement of responses innovel conditions, stimulus generalization was claimed as an outcome.

CLAIMS OF STIMULUS GENERALIZATION WITH RESPONSEPROMPTS AND REINFORCED RESPONSES

The published literature also shows that claims for stimulus generalizationhave been made when both response prompts and consequences were employed inthe nominal generalization setting as they were during original training. In a studythat tested the effect of activity schedules on task engagement by a child with

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autism, the initial training conditions were work and leisure activities (Massey& Wheeler, 2000). The child was taught to use activity schedules to control re-sponding during these two school activities. Lunch was designated as a stimulusgeneralization condition; however, the same instructional procedures used duringthe work and leisure training conditions were employed for the lunch activity.

CRITIQUE OF STIMULUS GENERALIZATIONTESTING PROCEDURES

In all of the studies previously cited, the goal was to extend responding toadditional members of the relevant stimulus class, and that is a commendable out-come. The use of prompts and differential reinforcement to strengthen responsesemitted in the presence of multiple neutral stimuli designated to become classmembers is an appropriate tactic. Those responses, however, come under the con-trol of stimulus class members by direct training. Responses that emerge in thepresence of additional nontraining stimuli during extinction conditions help expandthe breadth of the stimulus class by generalization. Thus, control by the stimulusclass can occur as a result of both direct training and stimulus generalization.

As exemplified in the studies cited, there is a deviation between the traditionallaboratory procedures for testing stimulus generalization and the experimentalpreparations in those applied studies. The issue is not merely a semantic quibble, butwhat we really know and how we come to know it. A problem that this proceduraldiscrepancy creates is that it leads to claims of effects that are not true by traditionaldefinition. When one considers the outcome claims of these applied studies withoutknowing their experimental preparations, it can lead readers to overestimate thepower of the acquisition training procedures. It can be misleading to imply or inferthat generalization occurred when, in fact, the spread of effect to other stimulusclass members was trained. This can result in confusion in what we really knowin a body of literature, such as behavioral education and training.

The procedural veering from laboratory tradition may have its roots in theapplied behavior analysis literature of the late 1960s and 1970s. In the landmarkarticle that defined applied behavior analysis, generality of behavior change wasidentified as one of its characteristics (Baer, Wolf, & Risley, 1968). Generality of abehavior, according to these authors, refers to its durability over time (i.e., responsemaintenance), occurrence in a variety of appropriate environments (i.e., stimulusgeneralization), and spread to a variety of functionally related behaviors (i.e.,response generalization). The latter two outcomes essentially define generality interms of the breadth of the stimulus and response classes, respectively.

The term “generality”, as defined above, casts a wide net to encompass severaldistinct behavioral outcomes. This and related issues regarding the terms “gen-eralization” and “generality” have been discussed previously (Cooper, Heron,& Heward, 1987; Johnston, 1979; Johnston & Pennypacker, 1993). Instead of

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focusing on the concept of generalization, consideration should be directed moreproperly to the concept of “class” and the alternative means of expanding the tar-geted class membership to produce functional outcomes. Generalization is onlyone of those means, albeit an efficient one when it occurs. In addition to or in theabsence of generalization, stimulus classes can be broadened by various forms ofdirect training in the presence of their intended class members. It also is importantto teach learners to discriminate with precision and not respond in the presenceof stimuli that would not occasion functional responses (Albin & Horner, 1988).Class membership should be appropriately expanded and delimited.

During the 1970s, there were calls for analyzing and producing generalityof behavior change, and strategies were extracted and classified from the litera-ture that explicated how generalization could be promoted (Stokes & Baer, 1977).These authors defined generalization more expansively than traditional laboratorydefinitions (e.g., Catania, 1998). Stokes and Baer acknowledged that generaliza-tion includes the occurrence of the target behavior under non-training conditionswithout benefit of the original training procedures. This component of their defini-tion is in keeping with laboratory tradition. In addition, Stokes and Baer proposedthat generalization can be claimed if the desired behavior is achieved when someforms of intervention are employed, but with less investment than required to pro-duce the original results. This extension of the definition permits the training ofresponses that are then claimed as generalization outcomes. With this permissivedefinition as background and a menu of strategies to promote generalization byvarious training techniques, such as those indicated by Stokes and Baer, the contextwas present for the accumulating body of applied studies today whose conclusionsregarding stimulus generalization require methodological scrutiny.

More than 20 years ago, Michael (1980) observed that the behavioral proce-dures used as independent variables by some applied researchers were beginningto loose continuity with basic behavioral principles. This seems to be the case withthe principle of stimulus generalization, as understood from the experimental anal-ysis of behavior literature, and stimulus generalization as tested by some appliedpractitioners. Michael attributed methodological deviations from traditional con-cepts , in part, to “. . . the outcome-cure orientation’s encouragement to manipulatesimultaneously anything that might work” (p. 9).

The argument presented here is that behavioral educators should focus onstimulus class formation and how that will be accomplished in an applied context,such as education and training settings. Responses to some members of the stimu-lus class should be trained initially with one or more behavioral techniques. Thesemembers of the potential class could be selected for training after due considerationto techniques to promote generalization (Horner, Dunlap, & Koegel, 1988; Stokes& Baer, 1977). After that training, other unprogrammed stimuli might emerge asclass members by generalization (i.e., under extinction conditions without any formof direct intervention). After consideration of the functionality of the members ofthe trained and emerged members of the stimulus class for the learner, responses

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could also be trained in the presence of still other stimuli desired for class mem-bership. The issue is not to restrict training under different stimulus conditions, butthe conceptual concern is inferring stimulus generalization when the effects canbe attributed to the use of response prompts, consequences, and other behavioralprocesses (Johnston, 1979; Johnston & Pennypacker, 1993). Behavioral educatorscan assert that they are expanding the stimulus class by training in the presence ofmultiple exemplars, for example, but they should differentiate for each exemplarits mechanism of entry into the class: training or generalization. Behavior analystsalso should not claim stimulus generalization without observing enhanced perfor-mance over baseline measures under non-training conditions (Barrios & Hartman,1988). It is recommended that the education and training literature remain faithfulto the definition of stimulus generalization and its testing requirements. To do sowill help us know what we know and why we know it.

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uct labels to adolescents with mental disabilities through the use of key words taught by peertutors.Education and Training in Mental Retardation and Developmental Disabilities, 30, 65–75.

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Dalrymple, A. J., & Feldman, M. A. (1992). Effects of reinforced directed rehearsal on expressive signlanguage learning by persons with mental retardation.Journal of Behavioral Education, 2, 1–16.

Donahoe, J. W. & Palmer, D. C. (1994).Learning and complex behavior. Needham Heights, MA:Allyn and Bacon.

Fickel, K. M., Schuster, J. W., & Collins, B. C. (1998). Teaching different tasks using different stimuliin a heterogeneous small group.Journal of Behavioral Education, 8, 219–244.

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Jones, G. Y., & Collins, B. C. (1997). Teaching microwave skills to adults with disabilities: Acquisitionof nutrition and safety facts presented as nontargeted information.Journal of Developmental andPhysical Disabilities, 9, 59–78.

Keller, F. S. & Schoenfield,W. N. (1950).Principles of psychology, New York: Appleton-Century-Crofts.

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Sandknop, P. A., Schuster, J. W., Wolery, M., & Cross, D. P. (1992). The use of an adaptive device toteach students with moderate mental retardation to select lower priced grocery items.Educationand Training in Mental Retardation and Developmental Disabilities, 30,219–229.

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to secondary students with moderate/severe disabilities: Facilitating observational learning dur-ing instructional downtime.Education and Training in Mental Retardation and DevelopmentalDisabilities, 3, 342–353.

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Williams, G., Donley, C. R., & Keller, J. W. (2000). Teaching children with autism to ask questionsabout hidden objects.Journal of Applied Behavior Analysis, 33,627–630.

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