Indeed, N400 data provided clear evidence for interactions of sentence context effects with word frequency, word level associations, and word repetition and revealed that, when both word- and sentence-level information sources were available, higher-level context effects tended to override lower-level ones, contrary to the then-prevailing assumptions of bottom-up priority for and insularity of word level processing (reviewed in Kutas 1993; Van Petten 1993). For example, the semantic constraints provided by a sentential context can supercede lexical frequency effects on the N400. Furthermore, when compared directly within the same materials, independent and qualitatively similar effects were obtained for lexical associative priming and sentence-level congruity: N400 amplitudes were reduced to lexically-associated second words in anomalous sentences as well as to unassociated words in congruent sentences, demonstrating the build-up of message-level meaning information over and above word-level associations. When both information sources were present, their influences were additive (with later work showing that even stronger message-level constraints override lexical association: Coulson et al 2005). These findings helped to establish that semantic congruity, repetition, and word frequency converge to influence a common stage of word processing: the modularity of lexical processing was irreparably penetrated by incisive N400 results.
