The grip of grammar on meaning uncertainty: cross-linguistic evidence, neural correlates, and clinical relevance

TL;DR

This study shows that grammar reduces meaning uncertainty across languages, reflected in brain activity and disrupted in language disorders, highlighting grammar's role in language comprehension and production.

Contribution

It introduces a cross-linguistic measure of how grammar compresses meaning uncertainty and links this to neural activity and clinical impairments.

Findings

Contextual surprisal reduces frequency-based surprisal across 20 languages.

Surprisal reduction correlates with complex dependency structures.

Disrupted surprisal reduction observed in aphasia, dementia, and schizophrenia.

Abstract

Isolated word meanings are inherently uncertain. This uncertainty reduces when they are combined and anchored in context. We propose that grammar compresses meaning uncertainty cross-linguistically, which is reflected in brain and selectively disrupted in disorders. Compression was operationalized as the relative difference between non-contextual surprisal estimated from lexical frequency, and contextual surprisal from grammar-sensitive models. In narratives from 20 languages, contextual surprisal reduced frequency-based surprisal. This reduction closely tracked the surprisal cost of reversing word order, and scaled with richer, non-redundant lexis as organized by more complex but optimal dependency structure. During fMRI, surprisal and its reduction explained BOLD activity for comprehension and production in overlapping but distinct regions. Uncertainty reduction was significantly attenuated in aphasia, dementia, and schizophrenia, but remained intact where primary deficit is not language. These findings position uncertainty reduction via grammar as a foundational concept that illuminates principles, brain basis, and disruptions of language.