On the distinctiveness, independence, and time course of the brain responses to syntactic and semantic anomalies

We evaluated the distinctiveness, independence, and relative time courses of the event-related brain potentials (ERPs) elicited by syntactically and semantically anomalous words. ERPs were recorded from 13 scalp electrodes while subjects read sentences, some of which contained a selectional restriction violation (semantically anomalous), a verb tense violation (syntactically anomalous), or a doubly anomalous word that violated both selectional restriction and verb tense constraints. Semantic anomalies elicited a monophasic increase in N400 amplitude, whereas syntactic anomalies elicited a late positive shift with an onset around 500 msec and a duration of several hundred msec. Doubly anomalous words elicited both an increase in N400 amplitude and a late positive wave, and these effects summated in an approximately (but not perfectly) linear manner. These results are discussed with respect to the hypotheses that syntactic and semantic processes are separable and independent.