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Aspects of the psychosis continuum

Aspects of the psychosis continuum. and the . Cardiff Anomalous Perceptions Scale. (CAPS). Vaughan Bell, Peter Halligan. Caroline Dietrich, Hadyn Ellis. School of Psychology, Cardiff University. Outline. What underlies the psychosis continuum ? Problems with existing scales

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Aspects of the psychosis continuum

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  1. Aspects of the psychosis continuum and the Cardiff Anomalous Perceptions Scale (CAPS) Vaughan Bell, Peter Halligan Caroline Dietrich, Hadyn Ellis School of Psychology, Cardiff University

  2. Outline • What underlies the psychosis continuum ? • Problems with existing scales • Cardiff Anomalous Perceptions Scale (CAPS) • Factors underlying anomalous perceptual experience. • The role of insight • Conclusions

  3. What underlies the psychosis continuum ? • Often described as a distribution of psychotic phenomena, that becomes pathological over a certain threshold. • Multiple contributory factors have been proposed, but are largely unidentified (Johns & van Os, 2001). • We were interested in identifying some of the factors underlying anomalous perceptual experience… • …but found current psychometric scales lacking. • Perhaps because they are derived from the assumptions of clinical psychiatry.

  4. Limitations of Existing Scales • Limited sensory range: • Often focus on visual and auditory experiences. • Assumption of how experience will present: • OLIFE: “When in the dark, do you often see shapes and forms even though there’s nothing there?” • RLSHS:“When I look at things they appear strange to me” • Focus on hallucinatory experience, excluding changes in intensity, sensory flooding etc..

  5. Limitations of Existing Scales • Ignore sensory anomalies associated with temporal lobe disturbance. • These have been linked to every ‘stage’ on the psychosis continuum: • Anomalous experiences in general population (Persinger and Makarec, 1987) • People with high levels of ‘paranormal’ beliefs (Makarec and Persinger, 1985) • Frank psychosis (Trimble, 1991)

  6. Cardiff Anomalous Perception Scale • 32 item self-report scale based on reviews of the perceptual anomaly literature. • Covers a range of sensory modalities, including proprioception, time perception, somatosensory, sensory flooding, changes in intensity etc. • Uses PDI-inspired ratings for distress, intrusiveness and frequency. • Ask about experiences from a number of ‘angles’ and does not assume experiences are ‘strange’ or ‘unusual’.

  7. Insight ‘angles’ of CAPS • A sensory experience with no obvious source. • A sensory experience which seems strange or unusual. • A non-shared sensory experience.

  8. CAPS: Psychometric Properties • Reliability: Internal α = 0.87; Test-retest = 0.77 – 0.79 • Convergent validity (non-clinical sample):

  9. * * * * * Evidence against 1-stage theories * * * Criterion and Discriminant Validity N = 337 N = 24 N = 24 N = 20 Significantly different from non-clinical sample at least p < 0.05 * Additional data from Nichola Smedley and Emmanuelle Peters

  10. Frequency Distribution

  11. Principal Components Analysis • Oblimin rotation on non-clinical population only. • Initial PCA suggested 7 factors, with clear break in scree plot after 3. • A three-factor, non-overlapping solution, interpreted as: • Chemosensation (largely olfactory, gustatory) • Clinical psychosis (first-rank symptoms) • Temporal lobe related (TLE, ‘microseizures’)

  12. ‘Clinical Psychosis’ Factor • Schneiderian first-rank symptoms. • May reflect the ‘threshold’ of pathology. • See Serper et al. (2005)

  13. ‘Temporal Lobe’ Factor • Gloor (1990) TLE: visual phenomena, music or sounds (usually without clear semantic content), relative lack of gustatory / olfactory experiences, distortion of time.

  14. ‘Temporal Lobe’ Factor • Items pre-selected as experiences from the non-clinical TL literature.

  15. TL Factor Validation • Standard linear regression, N=39 • DV: TL Scale (Markarec and Persinger, 1985) • IVs: CAPS Factors minus identical shared items. • TMS stimulation of TL alters detection of meaningful information in visual noise (Bell et al, in press)

  16. Rank Analysis • Compared the frequencies of items between clinical and non-clinical groups to give a rank difference. • Not a surprising difference, as ‘voices’ are a criteria for diagnosis. • Some categories of items are particularly informative.

  17. Rank Analysis of ‘Insight’ • Calculated mean rank difference for items in different ‘insight’ categories. • Sensory experience from an unexplained source barely differentiates clinical and non-clinical. • Whereas non-shared experiences do, ranking more highly in the clinical group.

  18. Conclusions • The CAPS is a valid, reliable scale for measuring anomalous perceptual experience. • There may be a number of factors underlying the psychosis continuum. • Temporal lobe disturbance is a likely candidate for one of the factors. • Having a perception that is experienced as not being shared by others may be most clinically significant.

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