Three Dimensions of Speech Coherence in People with Early Psychosis and Their Family Members

Alterations in speech coherence have long been noted in schizophrenia spectrum disorders (SSD). Three distinctive dimensions of such alterations are: (i) Use and distribution of noun phrases (NPs, e.g. a man; that large cat) in discourse; (ii) Semantic similarity between words or sentences; and (iii) Predictability of words (‘perplexity’). While these dimensions are likely to be inherently connected, they have largely been studied in isolation. This study targeted them in conjunction, in groups of first episode of psychosis (FEP, n=53) and youths at ultra-high risk (UHR, n=64) of SSD, in Turkish. Individuals with a family history of psychosis (FHP, N=39) were also included, and 34 neurotypical controls (NC). In FEP, we confirmed a pattern previously attested in chronic SSD in Turkish, 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. FEP and UHR also showed higher word-to-word semantic similarity, and FEP larger image-to-text bimodal semantic distance, replicating a pattern previously attested in English. NP-related variables related to both semantic similarity and perplexity, with crucially different patterns seen for definite vs. indefinite NPs. Referential anomalies (unclarities of reference) were more prevalent in all groups relative to NC. Together, these patterns confirm a referential disturbance in early psychosis, partially extending to the extended schizophrenia phenotype, while additionally confirming that referential structure is closely integrated with conceptual semantics and the probabilistic structure of speech