The present experiment explored the effects of three variables on the spontaneous categorization of stimuli in perceptually distinct and novel domains. Each of six stimulus domains was created by morphing two images that were the domain endpoints. The endpoints of the domains were male and female faces, two abstract drawings, a car and a truck, two banded-elevation satellite land images, a tree and a cat, and two false-color satellite images. The stimulus variants at each end of a domain defined two potential perceptual classes. Training was conducted in a matching-to-sample format and used stimuli from one or two domains, one or three variants per class as samples, and one or three variants per class as comparisons. The spontaneous categorization of stimuli in the untrained stimulus domains showed the emergence of a generalized categorization repertoire. The proportion of spontaneously categorized stimuli in the new domains was positively related to the number of domains and samples used in training, and was inversely related to the number of comparisons used in training. Differential reaction times demonstrated the discriminability of the stimuli in the emergent classes. This study is among the first to provide an empirical basis for a behavior-analytic model of the development of generalized categorization repertoires in natural settings.

Multiple-exemplar training with stimuli in four domains induced two new fill-based (A1' and A2') and satellite-image-based (B1' and B2') perceptual classes. Conditional discriminations were established between the endpoints of the A1' and B1' classes as well as the A2' and B2' classes. The emergence of linked perceptual classes was evaluated by the performances occasioned by nine cross-class probes that contained fill variants as samples and satellite variants as comparisons, along with nine other cross-class probes that consisted of satellite variants as samples and fill variants as comparisons. The 18 probes were first presented serially and then concurrently. Class-consistent responding indicated the emergence of linked perceptual classes. Of the linked perceptual classes, 70% emerged during the initial serial test. An additional 20% of the linked perceptual classes emerged during the subsequently presented concurrent test block. Thus, linked perceptual classes emerged on an immediate or delayed basis. Linked perceptual classes, then, share structural and fuctional similarities with equivalence classes, generalized equivalence classes, cross-modal classes, and complex maturally occurring categories, and may clarify processes such as intersensory perception.

After training conditional discriminations among selected stimuli from two perceptual classes, the emergence of novel relations involving other members of both classes was assessed using cross-class probes. The cross-class probes were presented using one of four different testing schedules. In the 2/9 test, nine different probes were presented in each of two test blocks. In the 6/3 test, three different probes were presented in each of six test blocks. In the 18/1-RND test, each of the 18 cross-class probes was presented in separate test blocks. In the 2/9 and 6/3 tests, the cross-class probes were presented in a randomized order within test block. In the 18/1-RND test, the cross-class probes were presented in a randomized sequence. In the 18/1-PRGM test, however, the cross-class probes were presented in a programmed order (i.e., the values of the stimuli in each cross-class probe were changed systematically in the succession of probe presentations). About 55% of the linked perceptual classes emerged during the 2/9, 6/3, and 18/1-RND tests. Thus the number of different probes in a test block did not influence the emergence of classes as long as the probes were presented in a random order. Virtually all classes emerged during the 18/1-PRGM test. Thus at least one ordered introduction of different cross probes resulted in the reliable emergence of linked perceptual classes. Mechanisms responsible for linked perceptual class formation are discussed along with the relation of these classes to other complex categories.

Two open-ended classes were formed when students were exposed to a forced choice primary generalization test, conducted in a matching-to-sample context. The classes were at opposite ends of a fill-based continuum. The endpoints of the continuum were called base stimuli and the intermediate stimuli were called variants. Class members were identified with tests conducted in the traditional variant-to-base format and a new base-to-variant format. The ranges of variants that functioned as members of the same nominal class differed with test format. In addition, the direction of that difference reversed for the classes at each end of the continuum. Followup tests showed that adjacent variants in a class were discriminable from each other. Thus, forced choice primary generalization tests induced classes of similar but discriminable stimuli. The fact that the same nominal class has two different widths raises a fundamental question about the definition of class membership. That issue is discussed along with recommendations for answering the question.Behavior that is controlled by categories or classes of stimuli is of great adaptive utility because it enables an individual to respond effectively to the new stimuli that are inevitably encountered in real world settings (Bruner, Goodnow,

When the stimuli in one perceptual class (A`) become related to the stimuli in another perceptual class (B`), the two are functioning as a single linked perceptual class. A common linked perceptual class would be the sounds of a person's voice (class A`) and the pictures of that person (class B`). Such classes are ubiquitous in real world settings. We describe the effects of a variety of training procedures on the formation of these classes. The results could account for the development of naturally occurring linked perceptual classes. Two perceptual classes (A`and B`) were formed in Experiment 1. The endpoints of the A`class were called anchor (Aa) and boundary (Ab) stimuli. Likewise, the anchor and boundary stimuli in the B`class were represented as Ba and Bb. In Experiment 2, the A`and B`classes were linked by the establishment of one of four cross-class conditional discriminations: AaRBa, AaRBb, AbRBa, or AbRBb. Results were greatest after AaRBb training, intermediate after AaRBa and AbRBa training, and lowest after AbRBb training. Class formation was influenced by the interaction of the anchor/ boundary values and the sample/comparison functions of the stimuli used in training. Experiment 3 determined whether class formation was influenced by different sets of two cross-class conditional discriminations: AaRBa and AbRBb, or AaRBb and AbRBa. Both conditions produced equivalent results. Similarities were attributable to the use of anchor stimuli as samples and boundary stimuli as comparisons in each training condition. Finally, the results after joint AaRBa and AbRBb training were much greater than those produced by summing the results of AaRBa training alone and AbRBb training alone. This same synergy was not observed after joint AaRBb and AbRBa training or either alone.