A non-verbal teaching program, combined with reinforcement and extinction (Program Group), was compared with reinforcement and extinction alone (Test Group) in teaching retarded children to discriminate circles from ellipses. In the Program Group, fading techniques were used to transfer stimulus control from "bright vs. dark" to "form vs. no-form" and then to "circle vs. ellipse". The Test Group had the task of learning the circle-ellipse discrimination with no prior teaching program. With the program, seven of 10 children learned the circle-ellipse discrimination. Without the program, one of nine learned. The eight Test-Group children who failed to learn circle vs. ellipse were then given the opportunity to learn the form no-form discrimination by reinforcement and extinction alone, without fading. Six of the eight learned, but only three of these six then learned circle vs. ellipse on a second test. All seven Program-Group children who had learned form vs. no-form also learned the circle-ellipse discrimination by means of fading; each of the seven made fewer errors than any of the three who succeeded on the second test. Children who failed to learn circle vs. ellipse adopted response patterns incompatible with the development of appropriate stimulus control.

This study examined stimulus class membership established via stimulus-reinforcer relations. Mentally retarded subjects learned conditional discriminations with four two-member sets of visual stimuli (A, B, C, and D). On arbitrary-matching trials, they selected comparison stimuli B1 and B2 conditionally upon samples A1 and A2, respectively, and C1 and C2 conditionally upon B1 and B2, respectively. On identity-matching trials, they selected all stimuli as comparisons conditionally upon identical stimuli as samples. Throughout training, correct selections of A1, B1, C1, and D1 were followed by one reinforcer, R1, and those of A2, B2, C2, and D2 were followed by another, R2. Subsequent tests documented the formation of two four-member stimulus classes, A1-B1-C1-D1 and A2-B2-C2-D2. The class membership of the A, B, and C stimuli could have been based on equivalence relations that resulted from the arbitrary-matching training. D1 and D2 had never appeared on arbitrary-matching trials, however. Their class membership must have been based on relations with R1 and R2, respectively. Results thus confirm a previous finding that stimulus classes can be expanded via stimulus-reinforcer relations. They also define more precisely the potential nature of those classes and the conditions under which class membership can be established.

In an arbitrary matching-to-sample procedure, two mentally retarded subjects learned conditional discriminations with two sets of stimuli. Each set included a spoken name (NI or N2), an object (01 or 02), and a printed symbol (Si or S2). One subject selected conditionally (a) 01 upon NI, and 02 upon N2, and (b) Si upon 01, and S2 upon 02. The other subject selected conditionally (a) Si upon NI, and S2 upon N2, and (b) 01 upon Si, and 02 upon S2. For both subjects, selections of 01 and Si produced one type of food, Fl; selections of 02 and S2 produced a different type of food, F2. Both subjects also learned identity-matching performances, selecting 01, 02, Si, S2, Fl, and F2 conditionally upon those stimuli as samples; Fl followed selections of 01, Si, and Fl; F2 followed selections of 02, S2, and F2. Matching performances consistent with stimulus class formation involving the names, objects, symbols, and foods were demonstrated on probe trials, even though these performances had not been taught explicitly. Next, new objects, Xi and X2, were presented on identity-matching trials, producing Fl and F2, respectively. Without further training, Xi was selected conditionally upon Ni, Si, and 01, and X2 was selected upon N2, S2, and 02. When the contingencies were changed so that selections of Xi and X2 were now followed by F2 and Fl, respectively, X2 was selected conditionally upon Ni, Si, and 01, and Xi was selected upon N2, S2, and 02. Class membership of Xi and X2 had apparently changed. This study provides evidence that reinforcers may become members of stimulus classes, and that new stimuli may become class members through relations with reinforcers.

Normally capable adults learned two-choice identity matching of three-digit numerals and arbitrary matching of physically dissimilar nonsense syllables. The stimuli were displayed on a computer terminal, and responses consisted of typing on the terminal's keyboard. In Experiment 1, every trial displayed a sample numeral, a comparison numeral, and three equal signs (= = =). The comparison stimulus was to be selected if it was identical with the sample; otherwise the equal sign was to be selected. This "single comparison" method was then used to show that arbitrary matching could be based upon either sample-S+ or sample-S- relations. In Experiment 2, a series of probe trials displayed a novel sample, a comparison stimulus from the arbitrary matching baseline, and = = =. Subjects typically selected = = =; they apparently were excluding the baseline comparison stimulus. Experiments 3 through 5 investigated which variables in training would lead to the selection of baseline comparison stimuli in response to novel samples. Behavior was usually unchanged when baseline training included relating comparison stimuli to as many as four different samples. Punishment contingencies were effective, but performance did not generalize unless those contingencies were applied in relation to more than one baseline comparison stimulus.