THE USE OF N400 IN STUDIES OF STIMULUS EQUIVALENCE: A REVIEW OF METHODS AND PARAMETERS

Abstract

The N400 is defined as an event-related brain potential that is sensitive to the semantic relations between stimuli. For instance, when a pair of words belong to the same semantic domain (e.g., monkey-banana), the N400 will be significantly reduced in comparison to the N400 evoked by unrelated words (e.g., monkey-carburetor). Notably, the N400 responses are also sensitive to the arbitrary stimulus-stimulus relations formed by matching-to-sample procedures (MTS), supporting the notion that stimulus equivalence is a behavioristic model of semantic relations. In this study, we presented a methodological review of studies on stimulus equivalence that used the N400 as dependent measure of “equivalent” and “non-equivalent” stimulus-stimulus relations formed by MTS procedures. First, we searched on databases for studies that used the descriptive terms “equivalence relations”, “matching-to-sample”, “MTS”, “N400”, “relational learning”, and “derived relations” on the title and the abstract. Then, we categorized the number of experiments in each study, population, nature of stimuli, the event-related brain potential used as a dependent measure and whether the critical probes comprised baseline, reflexive, symmetric or transitive relations. We found that the MTS variables differed substantially from one study to another. Considering that most of these MTS variables may be critical to the establishment of stimulus equivalence, we encourage follow-up studies that aim at verifying whether and to what extent they can be related to the N400 outcomes.Key-words: Matching-to-sample, equivalence-relatedness-based-procedure, stimulus equivalence, N400, semantic relations, methodological review.