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This is in contrast to a categorical view of psychosis, where psychosis is considered to be a particular (usually pathological) state, that someone either has, or has not.
Development of the concept
The categorical view of psychosis is most associated with Emil Kraepelin, who created criteria for the medical diagnosis and classification of different forms of psychotic illness. Particularly, he made the distinction between dementia praecox (now called schizophrenia), manic depressive insanity and non-psychotic states. Modern diagnostic systems used in psychiatry (such as the DSM) maintain this categorical view.
In contrast, psychiatrist Eugene Bleuler did not believe there was a clear separation between sanity and madness, and that psychosis was simply an extreme expression of thoughts and behaviours that could be present to varying degrees through the population.
This was picked up by psychologists such as Hans Eysenck and Gordon Claridge who sought to understand this variation in unusual thought and behaviour in terms of personality theory. This was conceptualised by Eysenck as a single personality trait named psychoticism.
Claridge named his concept schizotypy and by examining unusual experiences in the general population and the clustering of symptoms in diagnosed schizophrenia, Claridge's work suggested that this personality trait was much more complex, and could break down into four factors.
- Unusual experiences: The disposition to have unusual perceptual and other cognitive experiences, such as hallucinations, magical or superstitious belief and interpretation of events (see also delusions).
- Cognitive disorganisation: A tendency for thoughts to become derailed, disorganised or tangential (see also formal thought disorder).
- Introverted anhedonia: A tendency to introverted, emotionally flat and asocial behaviour, associated with a deficiency in the ability to feel pleasure from social and physical stimulation.
- Impulsive nonconformity: The disposition to unstable mood and behaviour particularly with regard to rules and social conventions.
The relationship between schizotypy and mental illness
Although aiming to reflect some of the features present in diagnosable mental illness, schizotypy does not necessarily imply that someone who is more schizotypal than someone else is more ill. For example, certain aspects of schizotypy may be beneficial. Both the Unusual experiences and Cognitive disorganisation aspects have been linked to creativity and academic achievement (e.g. research by Nettle, 2005).
However, the exact nature of the relationship between schizotypy and diagnosable psychotic illness is still controversial. One of the key concerns that researchers have had is that questionnaire-based measures of schizotypy, when analysed using factor analysis, do not suggest that schizotypy is a unified, homogeneous concept. The two main approaches have been labelled as the 'dimensional' and the 'quasi-dimensional' approach.
Each approach is sometimes used to imply that schizotypy reflects a cognitive or biological vulnerability to psychosis, although this may remain dormant and never express itself, unless triggered by appropriate environmental events or conditions (such as certain doses of drugs or high levels of stress).
The dimensional approach, influenced by personality theory, argues that full blown psychotic illness is just the most extreme end of the schizotypy spectrum and there is a natural continuum between people with low and high levels of schizotypy.
Support for the dimensional model comes from the fact that high-scorers on measures of schizotypy may meet, or partially fulfill, the diagnostic criteria for schizotypal disorders, such as schizophrenia, schizoaffective disorder, schizoid personality disorder and schizotypal personality disorder. Similarly, when analyzed, schizotypy traits often break down into similar groups as do symptoms from schizophrenia (although they are typically present in much less intense forms).
The quasi-dimensional approach argues that full blown psychosis is not just high schizotypy, but must involve other factors that make it qualitatively different and pathological.
Some researchers have argued that full-blown psychosis or schizophrenia requires the presence of a 'schizogene' or other specific inherited attribute in addition to high schizotypy. Further evidence that there is a non-linear relationship between schizotypy and some cognitive factors known to be affected in schizophrenia (such as latent inhibition) is also given as evidence for the quasi-dimensional approach.
- schizotypal personality disorder
- Claridge, G. (1997) Schizotypy: Implications for Illness and Health. Oxford University Press. ISBN 019852353X
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