Formal thought disorder (TD) is a neuropathology manifest in formal language dysfunction, but few behavioural linguistic studies exist. These have highlighted problems in the domain of semantics and more specifically of reference. Here we aimed for a more complete and systematic linguistic model of TD, focused on (i) a more in-depth analysis of anomalies of reference as depending on the grammatical construction type in which they occur, and (ii) measures of formal grammatical complexity and errors. Narrative speech obtained from 40 patients with schizophrenia, 20 with TD and 20 without, and from 14 healthy controls matched on pre-morbid IQ, was rated blindly. Results showed that of 10 linguistic variables annotated, 4 showed significant differences between groups, including the two patient groups. These all concerned mis-uses of noun phrases (NPs) for purposes of reference, but showed sensitivity to how NPs were classed: definite and pronominal forms of reference were more affected than indefinite and non-pronominal (lexical) NPs. None of the measures of formal grammatical complexity and errors distinguished groups. We conclude that TD exhibits a specific and differentiated linguistic profile, which can illuminate TD neuro-cognitively and inform future neuroimaging studies, and can have clinical utility as a linguistic biomarker.

The Grammar & Cognition Lab was supported by the Ministerio de Economía y Competitividad, Spanish Government, grants FFI2013-40526P, FFI 042177665-77665-4-16 to W.H. FIDMAG Germanes Hospitalàries Research Foundation is supported by the Agència de Gestió d'Ajuts Universitaris i de Recerca from Generalitat de Catalunya (2014-SGR-1573) and Miguel Servet Research Contract (CPII16/00018 to E. P.-C.) funded by Instituto de Salud Carlos III, co-funded by European Regional Development Fund/European Social Fund, "Investing in your future" . The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.