The relationship between language disorder and thought disorder: Comparing micro- and macrostructure of spoken narratives of people with aphasia and people with schizophrenia

Linguistic profiles in neurological and psychiatric conditions offer critical insights into the relationship between language and broader cognitive functions. People with aphasia (PwA) can display severe language production and comprehension difficulties, often alongside relatively preserved capacity in other domains. In contrast, people with schizophrenia (PwS) can present with disordered thoughts, delusions and hallucinations, accompanied by atypical language use. We examined microstructural (lexicon, syntax) and macrostructural (narrative) features of comic strip descriptions produced by PwA, PwS, and two respective control samples, using manual annotation and computerized tools. Both clinical groups diverged from controls at microstructural and macrostructural levels. However, PwA showed greater microstructural disruption, while PwS exhibited greater macrostructural impairment. Language production in PwA differed most from PwS in the much higher rate of morphosyntactic errors, more frequent intra-clausal pauses, and a greater reduction of grammatical complexity. In PwA, performance in non-verbal reasoning and semantics tests correlated with macrostructural, but not with microstructural measures. In PwS, non-verbal reasoning scores correlated with both micro- and macrostructural measures. These findings highlight distinct effects of more focal left perisylvian damage associated with aphasia, versus diffuse bihemispheric frontotemporal and parietal dysfunction associated with schizophrenia, on cognition and communication. We propose that verbal disruption with few morphosyntactic errors and intra-clausal pauses reflects broader cognitive dysfunction, whereas a high frequency of these features points to difficulties more specific to language production and comprehension.