Chapter 36: Personality and Psychosis

Interest in this area stems from the long-standing concept that features associated with psychosis exist along a continuum or dimension in the general population, even in people who do not meet clinical criteria for madness. Historically, two main research traditions inform this topic: one focusing narrowly on the schizophrenia concept, using terms like ‘schizoid’ (coined by Bleuler to describe odd or eccentric individuals) and later 'schizotypy' (developed by Rado and elaborated by Meehl to articulate the etiology of schizophrenia). The second tradition, rooted in theories of healthy individual differences, is exemplified by Eysenck’s broad dimension of ‘Psychoticism,’ which was developed based on Kretschmer’s continuum model and aimed to capture personality links to all psychoses, supporting the unitary psychosis theory—the idea that schizophrenia and manic-depression are variable expressions of a common process. This leads to the debate between the quasi-dimensional view (seeing general population psychotic features as merely attenuated forms or forme fruste of disease, usually focused on the schizophrenia spectrum) and the fully dimensional view (seeing psychotic traits as continuous parts of normal personality structure that shift into clinical symptoms under certain conditions). Research measuring these traits, often using self-report questionnaires like the Wisconsin Schizotypy Scales developed by the Chapmans (e.g., Perceptual Aberration, Magical Ideation, Anhedonia) or the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE), generally confirms that schizotypy/psychoticism is multidimensional. While many analyses reveal three major components (aberrant perception, cognitive disorganization, and interpersonal/anhedonic features), some analyses using a broader range of scales, including those for Hypomanic Personality and Borderline Personality, identify a fourth factor: Impulsive Non-conformity. The emergence of this fourth factor supports the unitary psychosis theory by linking schizophrenia-related traits with affective or bipolar disorder traits. Further inquiry into the latent structure of these traits, particularly through taxometric analysis, suggests that schizotypy is genuinely dimensional rather than defining a discrete, all-or-none category (taxon), contrary to some earlier claims. Longitudinal studies confirm that scoring highly on positive symptom scales (like Perceptual Aberration) predicts a greater likelihood of developing both schizophrenia and mood disorders, with positive symptoms correlating with high Openness to Experience and negative symptoms correlating with low Openness. Laboratory studies seek to identify endophenotypes—subtle indices of function that map onto risk, such as those related to Peter Venables’ theory of ‘input dysfunction,’ which posits that psychosis involves failure in inhibitory mechanisms that regulate stimulus processing in the nervous system. Finally, the chapter addresses the concept of the healthy face of psychosis, arguing that although clinical psychosis is severe, the underlying psychotic traits, particularly schizotypy, are inextricably linked to adaptive functioning, notably in the realm of creativity. Understanding how biological predispositions and personality traits interact with social and environmental triggers is key to determining why these traits translate into illness in some individuals but remain adaptive in others.