Three dimensions of speech coherence in people with early psychosis and their family members.

Abstract

Fundamental to coherence in discourse is referential structure - identifying entities through noun phrases (NPs, e.g. a man; that large cat) and tracking them in discourse. But coherence is also mediated by conceptual-semantic structure, as tracked through semantic similarity relations between words, and by predictability ("perplexity"). Alterations in speech coherence have long been noted in schizophrenia spectrum disorders (SSD) along all three of these dimensions. These are likely connected, but have largely been studied in isolation. This study targeted them together, in Turkish-speaking people with a first episode of psychosis (FEP, n = 53), youths at ultra-high risk (UHR, n = 64) of SSD, people with a family history of psychosis (FHP, N = 39), and 34 neurotypical controls (NC). In FEP, we confirmed a pattern previously attested in chronic SSD, of fewer definite NPs (e.g., this bald man), more "bare" NPs-i.e., lacking functional elements such as this/a -, and an unexpected random distribution of indefinite NPs; moreover, referential anomalies (unclarities of reference) were more prevalent in all groups relative to NC. FEP and UHR also showed higher word-to-word semantic similarity, and FEP larger image-to-text bimodal semantic distance, mirroring a pattern previously attested in English. NP-related variables related to both semantic similarity and perplexity, with crucially different correlational patterns seen for definite vs. indefinite NPs. Together, these results substantiate crosslinguistic evidence of a referential disturbance in early psychosis, partially extending to the extended schizophrenia phenotype, while additionally supporting that referential structure is closely integrated with conceptual semantics and the probabilistic structure of speech.