Neurolinguistic signatures of microvariation and language change: Individual production variability predicts morphosyntactic processing differences

This study investigates the neurophysiological and behavioral effects of exposure to grammatical microvariation, focusing on the relationship between individual production patterns and on-line sentence processing. We examine a unique context of ongoing morphosyntactic change in Norwegian participial agreement, which gives rise to widespread, near-continuous variation in agreement marking across dialects and speakers. Event-related potentials (ERPs) were recorded from 156 participants drawn from two dialect regions with extensive inter- and intra-speaker variability, as they read sentences in standardized Norwegian Bokmål containing either invariant (control) or variable/changing (target) grammatical forms. Results show that both group-level dialect background and individual production frequencies modulate sentence processing. Participants from regions undergoing dialect change exhibit attenuated P600 effects and more gradient acceptability judgments, and neural sensitivity to participial agreement violations is continuously modulated by individual age and spoken agreement rates. These findings provide evidence that language processing is dynamically shaped by fine-grained individual differences in linguistic experience - including community-level exposure, personal production frequencies, and sociolinguistic positioning within ongoing grammatical change - and that even narrow between- and within-individual variation in dialectal grammar influences integration costs during standard language comprehension.