Linguistic Creativity and Formal Thought Disorder in Schizophrenia

Delgaram-Nejad, Oliver (2024) Linguistic Creativity and Formal Thought Disorder in Schizophrenia. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Both linguistic creativity and formal thought disorder (FTD) are heterogeneously expressed and difficult to define. The present thesis develops operational definitions of these concepts by examining historic and contemporary accounts of FTD and the application of tests of creative linguistic ability with schizophrenia populations. The first of these definitions is operationalised as a novel theoretical framework (the 4TD Framework) that situates historic and contemporary descriptions of FTD in terms of linguistic levels of operation (phonology, morphology, syntax, semantics, and pragmatics), where FTD is conceptualised in terms of grammar, word selection, thought completion, and discourse tracking. The second positions linguistic creativity in schizophrenia as selectively constrained by schizophrenia symptoms and intellectual ability. These definitions are examined quantitatively using experimental psycholinguistic and corpus linguistic methods. The experimental psycholinguistic component involved the design of an original metaphor creation task. The task is described as original as it adapted design elements from three extant tasks for use with a schizophrenia cohort. The corpus linguistic component involved the design of a small, specialised corpus of spoken language. This corpus is the first of its kind at the time of writing and, unlike most other clinical corpora, is publicly available. The results from the systematic literature review support the view that figurative language comprehension is compromised in schizophrenia, and the results from the quantitative studies reveal that grammatical disturbances in everyday speech are more prominent in schizophrenia speakers. These disturbances appear to reside on a continuum with normal speech, and so a dimensional approach to FTD assessment is recommended. This is particularly important as most FTD assessment tools employ a categorical approach. In addition, schizophrenia speakers over-involve topics of emotional and personal concern when discussing abstract concepts. These findings are largely consistent with the extant literature on language in schizophrenia and FTD, however greater emphasis should be placed on grammatical features in the future. As FTD is considered a transdiagnostic phenomenon and a diagnostic criterion for schizophrenia, further work is needed to establish what is truly transdiagnostic. Further work on linguistic creativity in the affective psychosis spectrum, in combination with the work described here, can be assistive in this regard.