Seeing words in context: the interaction of lexical and sentence level information during reading.

The ERP experiment reported here addresses some outstanding questions regarding word processing in sentential contexts: (1) Does only the 'message-level' representation (the representation of sentence meaning combining lexico-semantic and syntactic constraints) affect the processing of the incoming word [J. Exp. Psychol.: Learn. Mem. Cogn. 20 (1994) 92]? (2) Is lexically specified semantic relatedness between multiple words the primary factor instead [J. Exp. Psychol.: Learn. Mem. Cogn. 15 (1989) 791]? (3) Alternatively, do word and sentence level information interact during sentence comprehension? Volunteers read sentences (e.g. Dutch sentences resembling The javelin was by the athletes...) in which the (passive) syntactic structure and the semantic content of the lexical items together created a strong expectation of a specific final word (e.g., thrown), but also sentences in which the syntactic structure was changed from passive to active (e.g. Dutch sentences resembling The javelin has the athletes...), which altered the message level constraint substantially and strongly reduced the expectation of any particular completion. Half of the sentences ended in a final word with a good lexico-semantic fit relative to the preceding content words (e.g. thrown, fitting well with the preceding javelin and athletes). This creates very plausible sentences in the strong constraint context but semantically anomalous ones in the weakly constraining context (e.g., The javelin has the athletes thrown). In the other half the final word had a poor lexico-semantic fit (e.g., summarized that does not fit at all with javelin and athletes). Good lexico-semantic fit endings showed no difference in N400 amplitude in the strong and weak message-level constraint sentences, despite the fact that the latter were semantically anomalous. This result suggests that lexico-semantic fit can be more important for word processing than the meaning of the sentence as determined by the syntactic structure, at least initially. These conditions did differ, however, in the region of the P600 where the anomalous weak constraint version was much more positive, a pattern usually seen with ungrammatical sentences. The processing of poor lexico-semantic fit words showed a quite different pattern; in both strong and weak constraint sentences they elicited a substantial N400 effect, but N400-amplitude was significantly more negative following strong constraint contexts, even though both sentence contexts were equivalently anomalous. Taken together, these findings provide evidence for the importance of both message-level and lexico-semantic information during sentence comprehension. The implications for theories of sentence interpretation are discussed and an extension of the message-based hypothesis will be proposed.