The structure of meaning in schizophrenia: A study of spontaneous speech in Chinese

Narrative speech production requires the retrieval of concepts to refer to entities, which need to be referenceable more than once for any form of narrative coherence to arise. Such coherence has long been observed to be affected in schizophrenia spectrum disorders (SSD), yet the underlying mechanisms have been a longstanding puzzle, with existing evidence predominantly derived from Indo-European languages. Here we analyzed two picture descriptions from 22 native Mandarin Chinese speakers with SSD and 15 healthy controls. An analysis scheme was created targeting key mechanisms in the genesis of referential meaning in speech. Results revealed that individuals with SSD used more definite-anaphoric noun phrases (NPs), which refer back to a previously mentioned entity in a narrative, and fewer NPs with adjectival modifiers. Definite NPs appeared earlier in their speech, and both definite and indefinite NPs occurred at shorter temporal distances. Participants with SSD referenced fewer entities, which in turn were more recurrent (referenced more than once). Furthermore, speech graphs capturing how entities are referenced across a narrative exhibited higher clustering, centrality, density, and shorter characteristic path lengths in SSD. Overall, these results from a non-Indo-European language support the new concept of a 'shrinking' or more condensed semantic space in SSD, impeding normal mental navigation across the concepts we retrieve during speech.