concept learning by retarded children: a comparison of three discrimination learning procedures

3. menu Defic. Res. (1982) 26, 229-238

CONCEPT LEARNING BY RETARDED CHILDREN: ACOMPARISON OF THREE DISCRIMINATION

LEARNING PROCEDURES

S. R. AESCHLEMAN*

Indiana University-Purdite University at Indianapolis, Indiana

AND

ANN F . HIGGINS

University ofKansaSy Kansas, USA

I N T R O D U C T I O N

In recent years there has been increasing interest in training techniques that producegeneralization to extra training situations. One generalization programming techniqueis to teach one exemplar of a generalizable lesson, then test for generalization to otherexemplars of that lesson. If generalization has not been engendered, another exemplarof the same lesson is taught, the generalization probe is readministered, and so on untilan established criterion of generalization has been achieved. Stokes & Baer (1977) havecalled this technique the training of sufficient exemplars. While this method has beenused extensively to generate response classes (Baer, Peterson, & Sherman, 1967; Guesseiai, 1968; Schumaker & Sherman, 1970), very little is known regarding the minimumnumber of exemplars necessary to produce generalization within and discriminationbetween stimulus classes (i.e. conceptual behaviour). Furthermore, it is not knownwhether different discrimination training procedures have differential effects on thisprocess. Although there is now ample documentation that procedures which add thengradually remove prompts to cue correct responding can facilitate acquisition of asingle, two choice discrimination relative to the method that provides only differentialreinforcement (Griffiths & Griffiths, 1976; Moore & Goldiamond, 1964; Sidman &Stoddard, 1967; Touchette, 1968), there is no direct evidence that such procedures arealso the optimal conditions for concept learning. It is possible that procedures whichadd then gradually remove cues may facilitate discrimination learning on each exemplarof a stimulus class, but retard generalization to other exemplars of that stimulus class.This hypothesis was first proposed by Gollin & Savoy (1968) who found that aprocedure that added then removed a cue from the learning situation attenuatedtransfer from a single discrimination to a conditional discrimination task. Gollin &Savoy suggested that the performance decrement during the conditional discrimination

"Address offprint requests to Stanley R. Aeschleman, Department of Psychology. IndianaUniversity-Purdue University at Indiana, 1201 East 38th Street, Indianapolis, Indiana 46223,USA.Received 14 January 19820022-264X/82/I200^0229$02.00 © 1982 Blackwell Scientific Publications

229

230 S. R. AESCHLEMAN and ANN F. HIGGINS

test could have resulted from the additional cue narrowing attention and thus providingthe subjects with insufficient comparative experience during discrimination training.

The purpose of the present experiment was to use the training of sufficient exemp-lars technique to determine the minimum number of exemplars required to generateconcept learning by retarded children trained on three different discrimination learningprogrammes. Two training conditions added then subsequently removed promptsfrom the learning situation by gradually increasing the saliency of the incorrect choice(stimulus fading) or gradually increasing the time between a prompt and the onset of thetrial (stimulus delay). In a third condition, reinforcement only, no prompts wereprovided. The stimulus fading method was first introduced by Terrace (1963) and hassubsequently been shown to facilitate discrimination learning by retarded children innumerous studies (Lambert, 1975; Sidman & Stoddard, 1967; Touchette, 1968).Touchette (1971) initially developed the stimulus delay method to measure the point atwhich control is transferred from the prompt to the criterion discrimination. Thestimulus delay method has since been used effectively as a teaching strategy (Johnson,1977; Stremel-Campbell, Cantrell, & Halle, 1977).

M A T E R I A L S A N D M E T H O D

Subjects

Twenty-four developmentally delayed children attending a preschool in Indianapolis,Indiana, served as subjects. The age range was from 30 to 65 months (mean of 52months). Developmental ages as determined by the Alpern-BoU Developmental Pro-file (Alpern & Boll, 1972) ranged from 18.0 to 50.8 (mean of 34.6). All subjects wereengaged in a summer school programme that ran concurrently with the present study.

Stimulus materials and setting

Choice of the target discrimination, bottle vs. jar, was based on two criteria: thediscrimination should be relatively difficult; and the concept should be absent from therepertoire of most preschool, developmentally delayed children. The training stimuliconsisted of five drawings of different types of bottles (e.g. one bottle had a rectangularbase, another a cylindrical base, etc.) and five drawings of different types of jars.Stimuli used in the pretest and the concept acquisition probe included five drawings ofobjects from stimulus classes other than bottle and jar (an obelisk, light bulb, hourglass, cup and flower pot) and the same 10 drawings used in the training phase. Allstimuli were drawn on 10.3x 10.3 cm squares of white paper and mounted on 21.8x21.8 cm Mead Notebook divider cards with black electrical tape.

The experiment was conducted with subjects seated next to the experimenter at atable in a 4.75x7.62 m room. The room contained a one-way mirror through which anobserver occasionally conducted inter-observer reliability checks.

Procedure

Figure 1 outlines the sequence of procedures employed during the experiment. Allchildren received an identical pretest session to determine whether the target concepts

CONCEPT LEARNING BY RETARDED CHILDREN 231

I START I

RANDOM A88IONMEMT OF

SUBJECTS TO OflOUPB

CONDUCT

PRETRAININQ

EXIT

EXPERIMENTy

CONDUCT TRAINING ON

ONE PAIR OF EXEMPLARS

PRESENT CONCEPT

ACQUISITION PROBE

Figure 1. Summary of the sequence of procedures used in ihe experiment.

(bottle and jar) were presently in their repertoire. Children who failed the pretest (fewerthan 80% correct responses) were randomly assigned to one of three experimentalgroups, 'stimulus fading', 'stimulus delay', or 'reinforcement only', and entered thepretraining phase. Children who passed the pretest were not included in the study.Pretraining was used to establish stimulus control by the cues employed to promptresponding during training in the 'stimulus fading' and 'stimulus delay' conditions.


After completing pretraining, subjects received training on the target concepts. Thetraining phase of all three experimental conditions contained five separate trainingprogrammes, each designed to teach the child to discriminate one type of bottle fromone type of jar. Upon entering the training phase, the subject received training on onepair of bottle and jar exemplars. When the learning criterion was reached on the firstpair of exemplars, a concept acquisition probe was administered. The concept acquisi-tion probe determined whether generalization to other types of bottles and jars wasengendered by the training programme. Children who reached criterion (80% correctresponding) on the concept acquisition probe received no further training. However,children who failed the concept acquisition probe returned to the training phase fortraining on a second pair of bottle and jar exemplars. Alternate presentations ofsuccessively different training programmes and concept acquisition probes were con-tinued until the subject passed the probe, failed to complete a training programme, orcompleted all five training programmes. This alternation of training on differentexemplars and concept learning probes was used to determine which procedure gener-ated conceptual behaviour with training on the fewest number of exemplars. Thespecific procedures employed in each phase are described below.

Pretest and concept acquisition probe. Both the pretest and concept acquisition probecontained 20 trials. Fifteen of the trials presented paired combinations of the bottle andjar exemplars. These stimulus pairs were randomly chosen from the 25 combinations ofthe five different types of bottles and five different types of jars. The remaining fivetrials presented a drawing of one of the objects from stimulus classes other than bottleand jar with a randomly chosen drawing of one type of jar or bottle. The inclusion ofthese additional objects provided a more rigorous test of conceptual behaviour.Stimulus location and order of presentation were determined randomly.

Pretest and concept acquisition probe sessions began with the experimenter sittingbeside the child with the stimulus cards placed face down in front of the child. Theexperimenter then gave the following instructions: 'We are going to play a game. I willask you to touch a picture. See if you can touch the right one'. Then the experimenterturned over the first card and told the child to touch the correct one for that trial (e.g.'Touch bottle'). If on the initial trial the subject did not respond or responded inappro-priately by touching both cards, the child's hand was guided to the correct choice. Onsubsequent trials, no other prompts were given. A response to either of the two stimulior a failure to respond within eight sec. terminated the trial. 'Cookie Monster' or'Kermit the Frog' hand puppets were presented following correct and incorrectresponses on a variable ratio three schedule. This procedure was used to maintainresponding without providing differential feedback for correct and incorrect responses.Upon presentation of the puppet, the experimenter praised the child through thepuppet (i.e. the experimenter moved the puppet's mouth and imitated the vocalizationsof the character). The puppet was kept out of sight under the table when not in use.

Pretraining. The purpose of pretraining for the 'stimulus fading' and 'stimulusdelay' conditions was to generate stimulus control by the prompts used in the subse-quent training programmes. Because success on the initial steps of the 'stimulus fading'training programmes required a discrimination between a white card containing animage (e.g. a drawing of a bottle or jar) and a completely darkened card, children in the'stimulus fading' group received pretraining on an image-no image discrimination


problem. The images were 10 randomly chosen Roman alphabet letters drawn on 4x4cm squares of white paper. A blackened 4x4 cm square of paper covered with a matteacetate overlay represented the no image stimulus. In the 'stimulus delay' conditionsuccessful completion of early steps in the training programme depended upon thechild being under stimulus control of a pointing cue. Consequently, for children in thisgroup, pretraining consisted of presentations of pairs of the Roman alphabet letterswith a pointing prompt to one of the letters indicating the correct choice. At thebeginning of each trial, the experimenter pointed to one of the letters while simultane-ously instructing the child to 'touch one'. The location of the experimenter's pointingcue was determined randomly. Subjects in the 'reinforcement only' condition alsoreceived pretraining as a control for warm-up effects. Pretraining for this group wasidentical to that received by the 'stimulus delay' group with the exception that nopointing cue was employed. Each subject in the 'reinforcement only' group was yokedwith one child from the 'stimulus fading' group and one child from the 'stimulus delay'group and received trials and reinforcers equal to the average given to this pair.

The learning criterion for the 'stimulus fading' and 'stimulus delay' groups waseight consecutive correct trials. The instructions and procedure for presentation ofstimuli were the same as the pretest with the exception that in the present phase theexperimenter said, 'Touch one', at the beginning of a trial. Five-second presentations ofone of the hand puppets followed correct responses while incorrect responses resultedin the experimenter looking away from and ignoring the child for 5 s.

Training. All experimental conditions contained five training programmes, eachrequiring the child to discriminate one type of bottle from one type of jar. A trainingprogramme contained 26 pairs of stimulus cards. For the 'stimulus fading' condition,the incorrect choice was gradually faded in across ten steps during the presentation ofthe first 20 stimulus cards (two cards per step so that both a bottle and a jar were thecorrect choice on a fading step). Fading was accomplished with grey matte acetateoverlays (Letraset 217). On the first fading step, 10 sheets of overlay were placed overthe incorrect choice. On the next step, nine sheets of overlay were placed over theincorrect choice, and so on until the last step where only one sheet covered the incorrectchoice. Subsequent to the fading series, six criterion stimulus cards were presented inwhich both stimuli were equally and maximally salient.

For the 'stimulus delay' group, all pairs of stimuli were presented at equal andmaximal saliency and a touch cue was presented in the following manner. Initially, thechild was given instructions to touch the correct choice with the experimenter simul-taneously touching the stimulus. After successful completion of a step, the touch cuewas delayed 0.5 s. That is, for the first step there was no delay between the task requestand the cue, but on the second step the task request and cue were separated by 0.5 s.The delay was incremented by 0.5 s through 10 steps which resulted in a 4.5 s delay onthe tenth step. The length of the delay was determined by the experimenter countingsilently 'one' for the 0.5 s delay, 'one, two' for the 1.0 s delay and so on until the last stepwhere the experimenter counted from one to nine. During presentations of the last sixstimulus cards, no touch cue was given. The training programmes for the 'reinforce-ment only' group were identical to the 'stimulus delay' condition with the exceptionthat no touch cue was given on any trials.

As in the pretest phase, during training the child and experimenter sat at a table in


front of the stimulus cards and the child was instructed to touch the correct choice forthat trial. The location and order of presentation of the two stimuli varied randomlyfrom trial to trial. According to a continuous schedule, a puppet appeared for 5 s andverbally praised the child after responses to the correct choice. A failure to respondwithin 8 s or an incorrect response terminated the trial, produced a 5 s time-out duringwhich the experimenter ignored the child, and backed-up the programme one step. Theback-up procedure ensured that subjects in the 'stimulus fading' and 'stimulus delay'groups returned to an easier step in the programme (Hively, 1962). The last six trialsused a back-up procedure such that if an incorrect response occurred on two trials thesubject returned to the next to last fading/delay step and continued to cycle in thismanner until five of the last six trials were responded to correctly or the criterion forfailure to learn was met. The criterion for failure to learn was 100 trials.

R E S U L T S

Inter-observer reliability data were periodically collected by an observer in an observa-tion room adjacent to the experimental room. Reliability was obtained on subjectsduring training and probe sessions. The observer recorded the subject's response foreach trial and a triai-by-trial comparison was then made with the experimenter's scoringof the subject's response. Reliability was computed by dividing the total number ofagreements by the total number of trials presented during the session and multiplyingthe quotient by 100. Reliability ranged from 90.4 to 100 % with a mean of 97.1 %.

In this experiment, concept learning was demonstrated when a subject reached thecriterion of 8O'i ) correct responding on the concept acquisition probe. The efficacy of aprocedure for generating concept learning was measured by the number of stimulusclass members (i.e. bottle and jar exemplars) and number of trials to criterion. Percentcorrect responding was also computed to determine in which conditions errorlesslearning was attained or approached. Table 1 summarizes the performance of allsubjects on concept acquisition. An examination of each child's performance revealedthat more children in the 'stimulus fading' group learned the concepts than children inthe 'stimulus delay' and 'reinforcement only' groups. Five children in the 'stimulusfading' group learned the concepts while only three subjects in the 'stimulus delay'condition and four subjects in the 'reinforcement only' condition reached criterion onthe concept acquisition probe.

Of the children who acquired a discrimination on one pair of exemplars, nonerequired training on more than two pairs of exemplars to reach criterion on the conceptacquisition probe. In fact, three of the five learners in the 'stimulus fading' group and allthree learners in the 'stimulus delay' group acquired the concepts after training on onlyone pair of exemplars. On the other hand, it is noteworthy that all four learners in the'reinforcement only' condition required training on two pairs of exemplars beforereaching criterion on the concept acquisition probe. These differences were statisticallysignificant (x'(2)=7.2,P<0.05).

Because many children received training on only one pair of exemplars, the perfor-mance data on the first pair of exemplars provides the only meaningful comparison ofthe influence of the three procedures on discrimination learning. Analysisof the trials tocriterion data revealed no significant differences among the three groups F(2,21 )=0.12


Table I. Summary of the performance of each child in the training phase

GroupStimulus fading

JSDBCSAHKMCWJRAW

Stimulus delaySMssHOCFDOLBKGRA

Reinforcement onlyTFABRTCRMGSBJTRH

Exemplarsto criterion *

11122

FLFLFL

111

FLFLFLFLFL

2222

FLFLFLFL

Trials

4239423285

100100100

304426

100100100100100

70413243

100100100100

Exemplar IErrors %

4432

15192320

150

2527192422

15546

51394341

Correct

9090939482817780

9689

1007573817578

7888888649615759

Trials

2639

—

——

45402830

——

Exemplar 2Errors %

03

—

—

4312

—

Correct

10092

—

—

91939693

—

'FL^failed to learn.

P>0.05. However, analysis of the percent correct responding data did reveal asignificant effect F(2,21)=3.85,P<0.05. Analysisp(75r/we using the Duncan MultipleRange test (P<0.05) indicated that both the 'stimulus delay' and the 'stimulus fading'conditions significantly enhanced correct responding. Together, these data suggest thatthe prompts in the stimulus delay and stimulus fading programmes reliably controlledresponding early in the training sequence for most children, but that control was nottransferred to the target discrimination for some subjects. A trial by trial breakdown ofpercent correct responding shown in Table 2 confirmed this hypothesis. Examinationof these data revealed that for the 'stimulus fading' group, the breakdown in stimuluscontrol usually occurred at the point where the fading cue was removed. While theperformance of the children in the 'stimulus delay' group was more variable, there wasalso a large decrement in correct responding at the point at which the pointing cue wasno longer presented. The variability in responding was mainly due to children in thiscondition responding incorrectly prior to the presentation of the pointing cue.


Table 2. Mean percentage correci responding at each training step

Programme step

123456789

10

11

Stimulus fadingn

8888888888

% Correct

1001001001001009695879484

cue removed8 60

Stimulus delayn

8888888776

6

% Correct

100968082737184796590

67

Reinforcement onlyn

S887554444

4

% Correct

5866556779878090

10092

89

D I S C U S S I O N

Two outcomes of the present study are important to educators of handicapped children.First the study found that regardless of the training programme employed, training ontwo or fewer exemplars of a stimulus class was sufficient to engender concept learning inthose children who acquired a discrimination. This result supports the observation byStokes & Baer (1977) that often training on a small number of exemplars is sufficient toproduce generalization. Accordingly, this finding suggests that educational pro-grammes designed to generate conceptual behaviour using stimuli similar to thoseemployed in the present study need not contain a large number of exemplars. Further-more, contrary to the prediction extrapolated from Gollin & Savoy (1968), the presentstudy found that neither the stimulus fading nor the stimulus delay methods retardedgeneralization. In fact, for those children who learned a discrimination the oppositeresuh was obtained. That is, the stimulus fading and stimulus delay proceduresfacilitated generalization to other members of the stimulus classes.

Alternatively, results from the present investigation support a growing hterature(Cheney & Stein, 1974; Doran & Holland, 1979; Koegel & Rincover, 1976) that hasreported a failure of stimulus fading procedures to significantly facilitate discriminationlearning. In addition, the present study found that the stimulus delay method also failedto enhance learning. This finding is especially important because previous researchwith this method did not provide a comparison condition (Johnson, 1977; Touchette,1971).

The effectiveness of the stimulus fading and stimulus delay procedures relies on thesuccessful transfer of stimulus control from a stimulus that is added to the learningsituation to cue correct responding to the appropriate, target discrimination. That is, atsome point appropriate stimulus control must be generated so that reinforcers can beapplied to maintain it. Doran & Holland (1979) have presented evidence suggestingthat for successful transfer to occur, at some point, both the prompt added to cuecorrect responding and the critical feature(s) of the target discrimination must controlresponding. Of course, there is no guarantee that dual control and hence successful


transfer will occur. In fact, it is becoming increasingly clear that as the target discrimi-nation becomes more complex, because of subtle differences between stimuli (Doran &Holland, 1979) or when there is more than one basis on which to make the criteriondiscrimination (Cheney & Stein, 1974), the probability of successful transfer isdecreased. With these types of discrimination problems, correct responding is oftenmaintained only when the added cue is present and discriminable; once it is removederrors begin to occur and the target discrimination is not acquired. It was this pattern ofresponding that the majority of the subjects in the present experiment displayed. Theadded cue in the 'stimulus fading' condition reliably controlled responding whilepresent, but after its removal responding fell to just above chance. In the 'stimulusdelay' condition, the pointing cue also reliably controlled responding during the earlysteps of the training programme when the cue was presented with a delay sufficientlyshort to prevent anticipatory responses to the incorrect choice. When the delay becamelonger or the prompt was no longer presented, incorrect responses increasedsubstantially.

On the whole, these results are bad news for teachers of the severely handicappedwho may have inferred that the demonstrated effectiveness of stimulus fading andstimulus delay techniques with simpler stimuli would generalize to the more complexdiscrimination problems which comprise the vast majority of instructional materials.Clearly more research is needed to determine whether the effectiveness of stimulusfading and stimulus delay procedures are indeed limited to simple discriminationarrangements and, if such limits do exist, to develop new training programmes that willenhance acquisition of complex tasks. One recently developed technique that hasshown promise for enhancing performance on complex discrimination tasks is stimulusshaping (Schilmoeller el al., 1979). With this procedure, the criterion related features ofthe stimuli are exaggerated early in the training sequence, then gradually reduced.While the implementation of this method requires more time and ingenuity thanstimulus fading or stimulus delay, in the long run programmes employing this methodmay be more efficient if the simpler procedures are ineffective in teaching complexdiscriminations.

SUMMARY

The effectiveness of stimulus delay and stimulus fading procedures was compared withdifferential reinforcement only in training developmentally delayed children on aconcept learning task. Twenty-four children were randomly assigned to one of the threetreatment conditions. All three experimental conditions contained five discriminationprogrammes, each designed to teach the child to discriminate one pair of exemplarsfrom the target concepts bottle and jar. Following successful completion of one trainingprogramme, a concept acquisition probe was administered to determine whether thetarget concepts had been engendered. Alternate presentations of successively differenttraining programmes and concept acquisition probes were continued until the subjectpassed the probe, failed to complete a training programme, or completed all fivetraining programmes. Five 'stimulus fading' subjects, three 'stimulus delay' subjects,and four 'reinforcement only' subjects learned the concepts. All children who learned todiscriminate one pair of exemplars displayed conceptual behaviour after training on two


or fewer pairs of exemplars. It was suggested that the absence of pronounced differ-ences between conditions may have been due to the complexity of the task or the type ofprompts employed.

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concept learning by retarded children: a comparison of three discrimination learning procedures

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