Date on Master's Thesis/Doctoral Dissertation

8-2017

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Psychological and Brain Sciences

Degree Program

Clinical Psychology, PhD

Committee Chair

Lewine, Richard

Committee Co-Chair (if applicable)

Mast, Benjamin

Committee Member

Mast, Benjamin

Committee Member

Woodruff-Borden, Janet

Committee Member

Meeks, Suzanne

Committee Member

Eells, Tracy

Author's Keywords

psychosis; thought disorder; dimensionality

Abstract

Background: Bleuler saw thought disorder as the core defining feature of psychotic phenomena, reflective of the “splitting of the psychic functions” that occurred when, in the process of thinking, one’s ideas and feelings disconnect, becoming fragmented and competing functions. Unfortunately, interest in thought disorder as the conceptual core of psychosis was lost with rise of the modern DSM system, paralleling the shift towards a more simplistic, categorical way of defining psychiatric disorders. Aims: This study examined thought disorder from a dimensional perspective, with the aim of disentangling qualitative heterogeneity and diverse sources of influence. Analyses were based on a large, transdiagnostic sample (n = 322), including individuals diagnosed with schizophrenia, schizoaffective disorder, and bipolar disorder. Structural equation modeling was used to estimate the unique and combined effects of family psychiatric history, age-at-onset, affective state, and sex on two dimensions of thought disorder, namely idiosyncratic thinking and combinatory thinking. We also explored the utility of categorical (i.e. DSM) diagnosis, by estimating the relative proportion of variance it accounted for within the model. Results: The overall model accounted for 11% of variance in idiosyncratic thinking and 3% of the variance in combinatory thinking. Negative affect was the strongest predictor of idiosyncratic thinking (r = .27), although this effect was significantly more robust in those with a family history of psychosis (r = .37) compared to those without (r = .02). DSM diagnosis was a significant predictor of IV, explaining 7% of unique variance when entered into the full model compared to 9% of the variance when estimated independently, which suggests that the portion of variance explained by diagnosis was largely independent of other predictors in the model. Discussion: The pattern of associations among family psychiatric history, age-at-onset, and negative affect that predicted idiosyncratic thinking are suggestive of a developmental process. This hypothesis is explored in the context of previous research. The broad implications of this research on the classification and study of psychosis is also discussed.