Deficits in nominal reference identify thought disordered speech in a narrative production task

Abstract

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.

Language disintegration under conditions of severe formal thought disorder

“…Results partially supported and partially contradicted our main predictions. They did not support our expectations motivated by previous studies (Rochester & Martin 1979;Wykes & Leff 1982;Harvey 1983;McKenna & Oh 2005), which had highlighted problems with pronouns and vague and unclear reference in spontaneous schizophrenic speech, while Cokal et al (2018) and Sevilla et al (2018) specifically highlighted problems with definiteness. Our results suggest that at least in severe FTD of the kind studied here and in a conversational task of this nature, the referencing problem seen in such patients is more general and reaches deeper into the organization of language, as opposed to primarily affecting pronominal or definite forms of reference, as we had predicted.…”

“…Unlike in Sevilla et al (2018), the proportion of anomalous lexical NPs turned out here to be significantly higher than that of pronouns. This could initially suggest that the problem increases when lexical content is involved, not when reference is not lexically mediated and in this sense more grammatically mediated, as in the case of pronouns.…”

“…This failure to replicate results on definiteness in previous studies may be partially due to the fact that two of the studies mentioned above that have investigated this issue most directly (Sevilla et al 2018 andCokal et al 2018), used narrative tasks, namely a fairytale retelling task and a retelling of a visually presented comic strip, respectively. These studies found that anomalies in definite NPs (Sevilla et al 2018), and in the quantitative proportions of definite vs. indefinite NPs (Cokal et al 2018), are linguistic identifiers of FTD as compared with controls and patients without FTD. But the tasks in question constrain the referential process more than the conversational task used here: a fairytale already provides a plot that is memorized, and in the case of the comic strip, the referents were visually present as and when the story was told.…”

“…Our annotation scheme thus covers (i) referential anomalies as linked to their linguistic substrates (NP types in which they occur), (ii) argument structure, (iii) lexis, and (iv) (morpho-) syntax. Based on Sevilla et al (2018) and Cokal et al (2018) we predicted that:…”

“…Recent linguistic work on FTD further supports a focus on NPs. One recent study (Sevilla et al 2018) compared the proportions of anomalous NPs in a group of Spanish-speaking patients with FTD (N = 20) against a second group with schizophrenia without FTD (N = 20) and neurotypical controls (N = 14), with data obtained from a fairytale retelling task. This study reported a significant difference between groups when anomalies in the referential NPs were annotated as occurring in definite NPs and pronouns, but not when annotated as occurring in indefinite NPs and lexical NPs (NPs containing a lexical noun), suggesting a specific linguistic signature of FTD speech.…”