The N400 as an index of lexical preactivation and its implications for prediction in language comprehension

ABSTRACT

The N400 component's amplitude is standardly reduced for predictable words. But it is not clear whether this reduction truly reflects preactivation of the critical word or whether it just indexes the difficulty of integrating the word with the sentence. To adjudicate between these two accounts, event-related potentials were recorded while participants read short stories. In half of the stories, just before the story-final sentence, we induced an explicit prediction of a congruent or an incongruent target word, thereby preactivating this word. Inducing prediction for the incongruent target word eliminated the N400, fully supporting the preactivation theory. This implies that the N400 is a marker of prediction and that prediction is an essential aspect of sentence comprehension. In addition, an analysis of the ERPs on the words preceding the critical target word provides evidence on how the target word becomes preactivated by the context.

KEYWORDS:

• N400
• late N400
• sentence processing
• prediction

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Jakub M. Szewczyk http://orcid.org/0000-0003-4464-082X

Notes

1. Note that the version of prediction as preactivation is not necessarily the same as postulated by the predictive coding theory where prediction is seen as the facilitated processing of a stimulus at the neural level (see Lewis, Schoffelen, Schriefers, & Bastiaansen, 2016; see also Kuperberg & Jaeger, 2016 for an in-depth discussion of different levels of prediction).

2. The broad range of cloze probability values is due to the fact that the target words occur in stories with a broad range of constraint strength values. Within each context, the congruent target word is one of the most likely words, and thus is highly plausible with respect to its context. In Supplementary Materials (S2) we capitalise on the large variance of constraint strength values to test how constraint strength affects the magnitude of the Anterior Positivity effect.

3. A parallel analysis performed using baselines directly preceding the point of divergence between the induced-prediction and no-induced-prediction conditions yielded a similar, although noisier and less reliable pattern of results.

4. Even though some differences in the latency of the N400 have been reported (see e.g. Brothers et al., 2015), they are far smaller than the discrepancy obtained here.

5. The idea that the effects at prenominal words reflect an update of conceptual predictions has been independently proposed by Nieuwland et al. (2017). In an experiment designed specifically to test this hypothesis we have just obtained results fully supporting it. The results show that the effect at a prenominal word has causal consequences for the N400 on the following noun and its amplitude is graded, depending on the amount of prediction updating triggered. Moreover, the amplitude on the noun itself is also graded depending on the amount of prediction updating triggered by the preceding word (Szewczyk, 2017).

Additional information

Funding

This research was supported by Grant 2012/05/B/HS6/03718 from the National Science Centre Poland to Jakub Szewczyk and by a stipend to Jakub Szewczyk from the Foundation for Polish Science subsidy to Zofia Wodniecka (FOCUS programme).