Aspects of the psychosis continuum

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.

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

11. * * * * * 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

12. Frequency Distribution

13. 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’)

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

15. ‘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.

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

17. 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)

18. 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.

19. 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.

20. 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.