A predictive coding model of the N400

The N400 event-related component has been widely used to investigate the neural mechanisms underlying real-time language comprehension. However, despite decades of research, there is still no unifying theory that can explain both its temporal dynamics and functional properties. In this work, we show that predictive coding – a biologically plausible algorithm for approximating Bayesian inference – offers a promising framework for characterizing the N400. Using an implemented predictive coding computational model, we demonstrate how the N400 can be formalized as the lexico-semantic prediction error produced as the brain infers meaning from the linguistic form of incoming words. We show that the magnitude of lexico-semantic prediction error mirrors the functional sensitivity of the N400 to various lexical variables, priming, contextual effects, as well as their higher-order interactions. We further show that the dynamics of the predictive coding algorithm provides a natural explanation for the temporal dynamics of the N400, and a biologically plausible link to neural activity. Together, these findings directly situate the N400 within the broader context of predictive coding research. More generally, they raise the possibility that the brain may use the same computational mechanism for inference across linguistic and non-linguistic domains.</p

Flexible predictions during listening comprehension: Speaker reliability affects anticipatory processes

Available online 9 October 2019During listening comprehension, the identification of individual words can be strongly influenced by properties of the preceding context. While sentence context can facilitate both behavioral and neural responses, it is unclear whether these effects can be attributed to the pre-activation of lexico-semantic features or the facilitated integration of contextually congruent words. Moreover, little is known about how statistics of the broader language environment, or information about the current speaker, might shape these facilitation effects. In the present study, we measured neural responses to predictable and unpredictable words as participants listened to sentences for comprehension. Critically, we manipulated the reliability of each speaker’s utterances, such that individual speakers either tended to complete sentences with words that were highly predictable (reliable speaker) or with words that were unpredictable but still plausible (unreliable speaker). As expected, the amplitude of the N400 was reduced for locally predictable words, but, critically, these context effects were also modulated by speaker identity. Sentences from a reliable speaker showed larger facilitation effects with an earlier onset, suggesting that listeners engaged in enhanced anticipatory processing when a speaker’s behavior was more predictable. This finding suggests that listeners can implicitly track the reliability of predictive cues in their environment and use these statistics to adaptively regulate predictive processing.This research was partially funded by NSF (1024003) and NIH (R21 11601946)

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Anticipating syntax during reading: Evidence from the boundary change paradigm.

Previous evidence suggests that grammatical constraints have a rapid influence during language comprehension, particularly at the level of word categories (noun, verb, preposition). These findings are in conflict with a recent study from Angele, Laishley, Rayner & Liversedge (2014), in which sentential fit had no early influence on word skipping rates during reading. In the present study, we used a gaze-contingent boundary change paradigm to manipulate the syntactic congruity of an upcoming noun or verb outside of participants’ awareness. Across three experiments (total N=148) we observed higher skipping rates for syntactically valid previews (The admiral would not confess…), when compared to violation previews (The admiral would not surgeon…). Readers were less likely to skip an ungrammatical continuation, even when that word was repeated within the same sentence (The admiral would not admiral…), suggesting that word-class constraints can take precedence over lexical repetition effects. To our knowledge, these results provide the first evidence for an influence of syntactic context during parafoveal word recognition. Based on the early time-course of this effect, we argue that readers can use grammatical constraints to generate syntactic expectations for upcoming words

Anticipating Syntax During Reading: Evidence From the Boundary Change Paradigm

Previous evidence suggests that grammatical constraints have a rapid influence during language comprehension, particularly at the level of word categories (noun, verb, preposition). These findings are in conflict with a recent study from Angele, Laishley, Rayner, and Liversedge (2014), in which sentential fit had no early influence on word skipping rates during reading. In the present study, we used a gaze-contingent boundary change paradigm to manipulate the syntactic congruity of an upcoming noun or verb outside of participants' awareness. Across 3 experiments (total N = 148), we observed higher skipping rates for syntactically valid previews (The admiral would not confess . . .), when compared with violation previews (The admiral would not surgeon . . .). Readers were less likely to skip an ungrammatical continuation, even when that word was repeated within the same sentence (The admiral would not admiral . . .), suggesting that word-class constraints can take precedence over lexical repetition effects. To our knowledge, these results provide the first evidence for an influence of syntactic context during parafoveal word recognition. On the basis of the early time-course of this effect, we argue that readers can use grammatical constraints to generate syntactic expectations for upcoming words. (PsycINFO Database Recor