Michael (1985) distinguished between two types of verbal behavior: topography-based and stimulus selection-based verbal behavior. The current research was designed to empirically examine these two types of verbal behavior while addressing the frequently debated question, Which augmentative communication system should be used with the nonverbal developmentally disabled person? Four mentally retarded adults served as subjects. Each subject was taught to tact an object by either pointing to its corresponding symbol (selection-based verbal behavior), or making the corresponding sign (topography-based verbal behavior). They were then taught an intraverbal relation, and were tested for the emergence of stimulus equivalence relations. The results showed that signed responses were acquired more readily than pointing responses as measured by the acquisition of tacts and intraverbals, and the formation of equivalence classes. These results support Michael's (1985) analysis, and have important implications for the design of language intervention programs for the developmentally disabled.

Michael (1985) identified two types of verbal behavior, topography-based (e.g., speaking or using sign language) and selection-based (e.g., using a symbol board). Sundberg and Sundberg (1990) and Wraikat (1990) compared these systems in terms of the ease of learning object naming (tact) and giving the correct sign or pointing to the correct symbol on hearing the object name (intraverbal). Sundberg and Sundberg (1990) also compared them for the spontaneous development of a new relation, identifying the object when hearing its name (stimulus class formation or equivalence). The results of both studies favored the topography-based system, but in each case some subjects were not verbally skillful enough to learn either system and some learned both too easily to permit a useful comparison. The current study replicated the two previous ones by teaching the same two verbal relations and testing for the emergence of new relations, but adjusted the task to the subject's level of functioning during the experiment. This was accomplished by varying the number of object relations being learned, and by interspersing already learned tasks with the training of new tasks. As with the earlier studies, topography-based verbal behavior was easier to learn, and led to more new stimulus-class relations than selection-based verbal behavior. These data confirm the relevant theoretical analysis, and have practical implications for a change in current language training practices.

Covert verbal mediation was examined in an arbitrary matching-to-sample (MTS) preparation with a high-verbal group (college students) and a low-verbal group (adults with intellectual disabilities). Arbitrary relations were established between nonsense words, visual symbols, objects, and hand signs. Task difficulty was balanced for the groups based on errors during acquisition. All participants experienced a hand sign condition, and three MTS conditions each with a unique configuration of the comparison array: fixed location, random location, and all symbols the same. The same symbol condition was designed to impede a participant's ability to label individual symbols. The results showed that disrupting labeling adversely affected MTS performance for high-verbal participants, but not for low-verbal participants. The data suggest that high-verbal participants depended on mediating verbal behavior and joint control to assist them in finding the correct comparison stimulus. Low-verbal participants could not benefit from verbal mediating variables and likely relied on unmediated contingencies, or some form of nonverbal mediation. For the high-verbal group, 19 different putative emergent relations were identified as occurring at various stages of acquisition between the sample stimulus and the selection response. These emergent relations likely provided supplementary sources of stimulus control that participated in evoking MTS selection behavior.

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