Academic journal article The Psychological Record

Matching-to-Sample and Stimulus-Pairing-Observation Procedures in Stimulus Equivalence: The Effects of Number of Trials and Stimulus Arrangement

Academic journal article The Psychological Record

Matching-to-Sample and Stimulus-Pairing-Observation Procedures in Stimulus Equivalence: The Effects of Number of Trials and Stimulus Arrangement

Article excerpt

Arbitrary relations can be derived between words, events, or other stimuli without explicit training or association (Blackledge, 2003). These relations provide a framework by which the function of words, objects, events, or other stimuli can be evoked by other words, objects, events, or other stimuli. Such relations have been used to explain the development of emotional reactions to words, events, or objects that have not previously been encountered or that have never been explicitly paired with an aversive event (Dougher, Auguston, Markham, & Greenway 1994). By this argument, many human psychological problems are the result of the inadvertent pairing or association of objects or stimuli with each other.

Sidman (2009) provided an overview of the most studied of the arbitrarily derived relations, stimulus equivalence. Establishing stimulus equivalence experimentally normally starts by teaching the participant relations between pairs of stimuli. Multiple sets of three or more stimuli are normally used. For example, Set 1 may contain three stimuli (A, B, and C). Training may involve teaching the relations A = B and B = C. Equivalence relations are said to have emerged when the participant demonstrate the untrained reflexivity (A = A, B = B, and C = C), symmetry (B = A and C = B), transitivity (A = C), and equivalence (C = A) relations. Both matching-to-sample (MTS) and the stimulus-pairing-observation (SPO) procedures have been used to facilitate the emergence of equivalence relations.

The MTS procedure is based on operant learning. In this procedure, as outlined in Barnes-Holmes, Barnes-Holmes, Smeets, Cullinan, and Leader (2004), the participants are first presented with a sample stimulus (e.g., Al), and are then required to choose one of several comparison stimuli (e.g., Bl, B2, or B3). Feedback is provided for correct choices. Incorrect responses may result in feedback or in no consequence.

Once participants have achieved a preset criterion for correct responses on the training relations, they are then tested to see if they have developed the untrained relations. During testing, the participants do not receive feedback of any sort (Barnes-Holmes et al., 2004). Three different types of tests may be conducted: reflexivity, symmetry, and transitivity. In reflexivity tests, the participants are required to choose the comparison stimulus that is the same as the sample stimulus. In symmetry tests, the participants are required to demonstrate the reversal of the trained relationships (Barnes-Holmes et al., 2004). Transitivity tests involve the demonstration of relations between stimuli that have not appeared together in any of the training trials (e.g., if the trained relations are Al-Bl and BI-C1, then transitivity is demonstrated by choosing Cl when the sample stimulus is Al). Combining symmetry and transitivity demonstrates the reverse of the transitivity relation (e.g., choosing Al when Cl is the sample stimulus). The successful completion of all of these tests demonstrates the formation of a stimulus equivalence class. Not all studies have tested for all relations. Some studies have tested for just symmetry and equivalence (e.g., Leader, Barnes, & Smeets, 1996; Leader & Barnes-Holmes, 2001b). Green, Sigurdardottir, and Saunders (1991) tested for reflexivity, transitivity, and equivalence, but not symmetry. These studies assume that the development of the equivalence relation can occur only if the reflexivity, symmetry, and transitivity relations have developed. Sidman (1994) argued that demonstrating the equivalence relations shows that the other relations must have developed. However, failing to achieve equivalence in the test means it is not possible to say whether the other derived relations that were not specifically tested had developed.

MTS has been used as the basis of many equivalence-based studies, and it has been shown that it facilitates the formation of equivalence relations (e. …

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