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The current article reports the first attempt to test the Implicit Relational Assessment Procedure (IRAP), as a group-based measure of natural verbal relations, using both response-latency and event-related potentials as dependent variables. On each trial of the IRAP, participants were presented with lof2 attribute stimuli ("Pleasant" or "Unpleasant"), a positive (e.g., "Love") or negative (e.g., "Murder") target stimulus, and 2 relational terms, "Similar" and "Opposite," as response options. Participants were required to respond as quickly and accurately as possible across blocks of trials, with half of the blocks requiring responses that were deemed consistent (e.g., Pleasant-Love-Similar), and the other half inconsistent (e.g., Pleasant-Love-Opposite), with natural verbal relations. Shorter mean latencies were predicted for consistent than for inconsistent blocks. Two separate experiments supported this prediction. Event-related potentials, gathered during the second experiment, also proved to be sensitive to the IRAP, yielding more negative waveforms for inconsistent relative to consistent blocks of trials. A theoretical interpretation of the iRAP effect is offered, and important directions for future research are highlighted.
The study of human language and cognition has attracted increasing attention among behavior-analytic researchers, with a particular focus on stimulus equivalence and derived stimulus relations (e.g., Hayes, Barnes- Holmes, & Roche, 2001; Sidman, 1994). In a typical study of stimulus equivalence, a series of interrelated conditional discriminations are first re- inforced, and then a number of untaught but predictable stimulus relations are seen to emerge in the absence of explicit feedback or verbal instruction. During the training, for example, A-B and B-C matching-to-sample (MTS) responses might be taught. A series of test or probe MTS trials are then presented in which symmetry (B-A, C-B), transitivity (A-C), and combined symmetry and transitivity (C-A) may be observed in the absence of differential reinforcement. If these emergent or untrained patterns of responding occur, the stimuli are said to participate in an equivalence class or derived relation.
Much of the interest in stimulus equivalence arises from the argument that it may provide a functional-analytic model of semantic relations in natural language (e.g., Barnes & Holmes, 1991). Although the debate surrounding this claim is far from resolved (e.g., Hayes, Barnes-Holmes, & Roche, 2003), a number of researchers have attempted to use the equivalence procedure as a means of testing natural verbal...