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Lexical Prediction and Semantic Relatedness Interact in Sentence Processing: Evidence From ERPs

 John Hoeks, Gina Doedens and Laurie Stowe

During sentence processing, words are continuously recognized and integrated with the existing syntactic and semantic representation of a sentence. This integration is often supposed to be a rather 'passive' match of the lexical content of the incoming word with the representation that has been built so far. However, in some cases people are quite good at actively predicting the next word of a given sentence, at least in off-line tasks. The question is to what extent do readers use this predictive ability during on-line sentence processing. To investigate this issue we conducted an ERP-experiment, using sentences in which the syntactic structure, together with the content of the preceding words, leads the reader to expect a specific lexical item, such as 'gebakken' (baked) in 1a (the sentences are in Dutch; the literal English translation is given in parentheses).

1a. Het bruine brood werd door de bakkers GEBAKKEN.
1b. Het bruine brood werd door de bakkers BEDREIGD.
(lit: The brown bread was by the bakers BAKED / THREATENED.)

In 1b, this expectation is violated by the occurrence of 'bedreigd' (threatened), which makes the sentence implausible, and will presumably lead to difficulty in semantic integration. This difficulty will most likely lead to a N400-effect. However, the word 'bedreigd' not only violates a lexical prediction, it is also semantically unrelated to the words that make up the rest of the sentence. Passive, bottom-up integration would thus also predict a N400- effect. Therefore, we included two types of implausible sentences where the final words are either related or unrelated, but in which the syntactic structure does not support any expectation for a specific lexical item, as in 2a and 2b.

2a. Het bruine brood heeft de bakkers GEBAKKEN.
2b. Het bruine brood heeft de bakkers BEDREIGD.
(lit: The brown bread has the bakers BAKED / THREATENED.)

We found a significant interaction between lexical prediction (prediction vs. no prediction) and semantic relatedness (related vs. unrelated) on the amplitude of the N400 elicited by the final words. The N400-effect (relative to condition 1a) was smallest for sentences such as 2a, where the implausible word is semantically related but where there is no specific lexical prediction, and largest for sentences as 1b, which end with an unrelated word which does violate a specific prediction. The N400-effect for sentences with an unrelated word and no specific prediction (2b) was exactly in between. This suggests that syntactic structure and lexical content together create specific predictions of a lexical item; processing a word that does not fit this prediction then Becomes quite difficult.

Unexpectedly, we also found an interaction of lexical prediction and semantic relatedness on a P600-like effect which was present in all implausible sentences, relative to plausible ones such as 1a. The effect was largest for implausible sentences containing a semantically related word (1a), which presumably indicates that the largest effort to reanalyze an implausible sentence is made when the incorrect word bears a semantic relation to the other words in the sentence. This is compatible with the view that the P600 reflects a (syntactic) reanalysis process which can be initiated by either semantic or syntactic violations.


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