Language disintegration under conditions of severe formal thought disorder

On current models of the language faculty, the language system is taken to be divided by an interface with systems of thought. However, thought of the type expressed in language is difficult to access in language-independent terms. Potential inter-dependence of the two systems can be addressed by considering language under conditions of pathological changes in the neurotypical thought process. Speech patterns seen in patients with schizophrenia and formal thought disorder (FTD) present an opportunity to do this. Here we reanalyzed a corpus of severely thought-disordered speech with a view to capture patterns of linguistic disintegration comparatively across hierarchical layers of linguistic organization: 1. Referential anomalies, subcategorized into NP type involved, 2. Argument structure, 3. Lexis, and 4. Morphosyntax. Results showed significantly higher error proportions in referential anomalies against all other domains. Morphosyntax and lexis were comparatively least affected, while argument structure was intermediate. No differential impairment was seen in definite vs. indefinite NPs, or 3rd Person pronouns vs. lexical NPs. Statistically significant differences in error proportions emerged within the domain of pronominals, where covert pronouns were more affected than overt pronouns, and 3rd Person pronouns more than 1st and 2nd Person ones. Moreover, copular clauses were more often anomalous than non-copular ones. These results provide evidence of how language and thought disintegrate together in FTD, with language disintegrating along hierarchical layers of linguistic organization and affecting specific construction types. A relative intactness of language at a procedural, morphosyntactic surface level masks a profound impairment in the referential functioning of language.