Response-to-sample requirements in conditional discrimination procedures

Any acquired behavior whose primary function is to affect the sensing of stimuli is called an 'observing response ' (Donahoe & Palmer, 1994). When Wyckoff (1952) discussed the role of observing responses in discrimination learning, he referred to “any responses which result in exposure to the pair of discriminative stimuli involved ” (p. 431). Furthermore, Wyckoff emphasized that it is important to distinguish these observing responses from the responses on which rein-forcements are based. One can increase at-tending by altering the contingencies so that attention is directed to the relevant stimuli in the complex environment (McIlvane, Dube, & Callahan, 1996). Observing responses, and their effect on learning, can be studied in conditional discrimination training. In some discrimination training procedures the participants can be required to respond to the discriminative stimulus. A possible outcome of conditional dis-crimination training is formation of equiva-lence classes. Stimuli within a class are said to be equivalent when they are interchangeable with one another (Green & Saunders, 1998). The properties used to determine whether the directly trained relations are equivalent are reflexivity, symmetry, and transitivity (Sidman & Tailby, 1982). Three training structures used in condi-tional discrimination procedures are called one-to-many (OTM), many-to-one (MTO), and linear series (LS) (e.g., Saunders, Saun-ders, Williams, & Spradlin, 1993). The LS structure has shown to be the least effective in producing stimulus equivalence relation