Vol. 11, No. 5
Analyzing Semantic Processing Using Event Related Potentials
1 Department of Speech Pathology, Northwestern University
2 Department of Psychology, University of Oregon
The brain’s electrical response to violations of semantic or syntactic structure differs as a function of the type of violation. Recent event-related potential (ERP) studies have shown that violations of different syntactic structures elicit distinct brainwave patterns. Whether this is true for semantic violations, which canonically generate an N400, has not yet been systematically explored. This study performs an analysis of the semantic domain by examining ERPs recorded from eighteen young adults as they read sentences containing three classes of semantic violations: improbability, hyponymy, and negative polarity. Improbability anomalies elicited a robust N400 effect. By contrast, neither hyponymy nor negative polarity violations elicited an N400. Hyponymy anomalies elicited a sustained left anterior negativity that began at 500 msec post-onset while negative polarity elicited a small anterior negativity between 300-500 msec. Furthermore, although the three classes violate specific semantic properties, ERPs for all three classes included a late posterior positivity similar to that reported in studies of syntactic violations. Onset of the positivity varied for each class: improbability 540 msec, hyponymy 380 msec, negative polarity 500 msec. These data show that ERP responses in the semantic domain yield results as rich as those reported for syntactic violations. In addition, the results suggest a reevaluation of the syntax-semantics dichotomy made at the neural level by past ERP studies that have used the N400 as a specific marker of semantic violation and the late positivity as a specific marker of syntactic processing.