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

2026-05-02

AI Summary

This study addresses the inherent uncertainty of isolated word meanings and demonstrates that grammatical structure systematically reduces this semantic uncertainty across languages. For the first time, the compressive effect of grammar on semantic uncertainty is formalized into a quantifiable metric by comparing non-contextual (frequency-based) and contextual (grammar-sensitive model) surprisal measures. Analyses across 20 languages reveal that contextual information significantly lowers semantic uncertainty. Functional MRI data link this compression mechanism to activity in specific brain regions. Clinical comparisons further show that this grammatical compression effect is selectively impaired in aphasia, dementia, and schizophrenia, yet preserved in disorders without primary language deficits, thereby elucidating its neural basis, cross-linguistic universality, and clinical specificity.

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.

Problem

• meaning uncertainty
• grammar
• cross-linguistic
• neural correlates
• clinical relevance

Innovation

• grammar
• meaning uncertainty
• surprisal compression
• cross-linguistic
• neural correlates