Aspects of the psychosis continuum

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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
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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

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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.

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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 theres nothing there?
• RLSHS When I look at things they appear strange
  to me
• Focus on hallucinatory experience, excluding
  changes in intensity, sensory flooding etc..

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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)

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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.

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Insight angles of CAPS

• A sensory experience with no obvious source.
• A sensory experience which seems strange or
  unusual.
• A non-shared sensory experience.

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CAPS Psychometric Properties

• Reliability Internal a 0.87 Test-retest
  0.77 0.79
• Convergent validity (non-clinical sample)

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Criterion and Discriminant Validity
N 337
N 24
N 24
N 20
Significantly different from non-clinical sample
at least p lt 0.05

Additional data from Nichola Smedley and
Emmanuelle Peters
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Frequency Distribution
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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)

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Clinical Psychosis Factor

• Schneiderian first-rank symptoms.
• May reflect the threshold of pathology.
• See Serper et al. (2005)

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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.

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Temporal Lobe Factor

• Items pre-selected as experiences from the
  non-clinical TL literature.

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TL Factor Validation

• Standard linear regression, N39
• 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)

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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.

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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.

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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.