Cohesion profiles across language-related symptoms in schizophrenia

Language has long been considered central to the psychopathology of schizophrenia, yet the precise linguistic mechanisms underlying different symptom dimensions remain poorly understood. Cohesion, defined as the set of linguistic devices that connect utterances within discourse, has been studied extensively in formal thought disorder (FTD) but not, to our knowledge, with respect to the verbatim content of auditory verbal hallucinations (AVH). In this study, we conducted a detailed cohesion analysis of Spanish speech samples from four groups: individuals with schizophrenia without FTD (N = 20), individuals with clinically rated FTD (N = 20), individuals experiencing persistent AVH (N = 16), and healthy controls (N = 20). Using an adaptation of Halliday and Hasan's (1976) cohesion framework, we quantified lexis, reference, conjunction and ellipsis and examined their relation to clinical FTD severity. Results indicated that cohesion was preserved in schizophrenia patients without language symptoms, while thought-disordered speech showed a selective reduction in referential cohesion only. In contrast, AVH transcripts exhibited a strong and widespread reduction across all cohesion subtypes, even after controlling for IQ, transcript length and incomprehensible fragments. These findings suggest that cohesion is not a uniform linguistic vulnerability across schizophrenia but rather it appears to be preserved in patients without disordered speech, selectively impaired in the domain of referential ties among those with FTD, and profoundly diminished across all cohesive mechanisms in hallucinated speech.