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In his book, Verbal Behavior, Skinner (1957) defined verbal operants as behavior units that consist of identifiable responses that are functionally related to independent variables. These verbal operants include mands, tacts, intraverbals, and echoics. Skinner emphasized that since verbal operants are controlled by distinct variables, they should be functionally independent. Therefore, it is crucial to teach these verbal functions separately rather than assuming that they will naturally emerge together. However, if training one verbal operant leads to the emergence of another untrained operant, a more efficient approach to verbal behavior training can be developed.
Research on Functional Independence
Research has primarily focused on studying the functional independence of mands and tacts, although other relations have also been evaluated (e.g., Miguel, Petursdottir, & Carr, 2005). While early studies supported the concept of functional independence (Hall & Sundberg, 1987; Lamarre & Holland, 1985; Partington et al., 1994; Simic & Bucher, 1980; Twyman, 1996), more recent research has identified conditions that can lead to the transfer from one operant to another (Arntzen & Almas, 2002; Carroll & Hesse, 1987; Petursdottir, Carr, & Michael, 2005; Sigafoos, Doss, & Reichle, 1989; Sigafoos et al., 1990; Sundberg, San Juan, Dawdy, & Arguelles, 1990; Wallace, Iwata, & Hanley, 2006).
Evidence for Functional Independence
In one notable study by Lamarre and Holland (1985), three typically developing 5-year-old children were taught to mand and tact the abstract directions of “on the left” and “on the right.” Participants were trained to tact the placement of an object while others were trained to mand for the locations. The study revealed that the untrained operant did not emerge naturally, leading to the need for direct training. Reversal training was then conducted, where the meaning of the phrases was reversed. The results showed that direct training was necessary for the emergence of the reversed operant for most participants, while the transfer of control between verbal operants was unclear for a few participants.
Hall and Sundberg (1987) also demonstrated functional independence between mands and tacts in individuals with intellectual disabilities. The participants learned to complete behavior chains that resulted in direct reinforcement. They were then taught to tact the pieces required to complete the chains. Probes conducted during training revealed that mand responses only occurred after direct mand training.
Conditions for Functional Interdependence
Some studies have described conditions that can lead to functional interdependence or transfer between verbal operants (Arntzen & Almas, 2002; Carroll & Hesse, 1987; Petursdottir et al., 2005; Sigafoos et al., 1989, 1990; Sundberg et al., 1990; Wallace et al., 2006). For example, Wallace et al. (2006) taught participants with developmental disabilities to tact high-preference (HP) and low-preference (LP) items and then tested for the occurrence of mands. The study found that transfer of control between verbal operants was more likely to occur when highly preferred items were used. The authors suggested that the absence of transfer in earlier studies may have been due to the lack of highly preferred items during training.
Evaluating Functional Independence of Tacts and Mands
Petursdottir et al. (2005) further investigated the functional independence of tacts and mands in preschool children. Participants were trained to either mand or tact items in assembly tasks. During training, correct responses were reinforced with praise and stickers. The study found that all participants demonstrated the emergence of tacts after mand training. However, only two of the four participants demonstrated mands after tact training. The researchers hypothesized that self-echoic responding observed during mand training facilitated the transfer from mand to tact but not from tact to mand.
Assessing Transfer in Children with Autism
This study aims to expand upon the research conducted by Petursdottir et al. (2005) and Egan and Barnes-Holmes (2009) by assessing the transfer between mands and tacts during instruction with children with autism. Participants will be taught to either mand or tact parts of a construction task and will be tested for the emergence of the untrained verbal operant. The chosen tasks will ensure that the missing piece does not control the mand response during training and testing.
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Teaching verbal functions separately is crucial in developing effective communication skills. Research has shown evidence for both functional independence and interdependence between mands and tacts. By understanding the conditions that contribute to the transfer between verbal operants, we can optimize instructional procedures for individuals with communication challenges, such as those with autism.