4.6 Article

The P600 as a continuous index of integration effort

Journal

PSYCHOPHYSIOLOGY
Volume 60, Issue 9, Pages -

Publisher

WILEY
DOI: 10.1111/psyp.14302

Keywords

EEG; ERPs; language comprehension; N400; P600; psycholinguistics

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The integration of word meaning into an unfolding utterance representation is a crucial aspect of incremental language comprehension. This study aims to determine which component of the ERP signal, the N400 or the P600, is a direct reflection of integration processes. The results support the view that the P600 serves as a continuous index of integration effort and do not provide evidence for the N400 as a reliable indicator of integration. The findings also suggest a single-stream architecture and challenge the need for multi-stream accounts.
The integration of word meaning into an unfolding utterance representation is a core operation of incremental language comprehension. There is considerable debate, however, as to which component of the ERP signal-the N400 or the P600-directly reflects integrative processes, with far reaching consequences for the temporal organization and architecture of the comprehension system. Multi-stream models maintaining the N400 as integration crucially rely on the presence of a semantically attractive plausible alternative interpretation to account for the absence of an N400 effect in response to certain semantic anomalies, as reported in previous studies. The single-stream Retrieval-Integration account posits the P600 as an index of integration, further predicting that its amplitude varies continuously with integrative effort. Here, we directly test these competing hypotheses using a context manipulation design in which a semantically attractive alternative is either available or not, and target word plausibility is varied across three levels. An initial self-paced reading study revealed graded reading times for plausibility, suggesting differential integration effort. A subsequent ERP study showed no N400 differences across conditions, and that P600 amplitude is graded for plausibility. These findings are inconsistent with the interpretation of the N400 as an index of integration, as no N400 effect emerged even in the absence of a semantically attractive alternative. By contrast, the link between plausibility, reading times, and P600 amplitude supports the view that the P600 is a continuous index of integration effort. More generally, our results support a single-stream architecture and eschew the need for multi-stream accounts.

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