The Psychosis Continuum and the

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The Psychosis Continuum and the
Cardiff Anomalous Perceptions Scale (CAPS)
Are there multiple factors underlying
anomalous experience?
Vaughan Bell1,2, Peter Halligan2, Hadyn Ellis2
1Institute of Psychiatry, Kings College London
2School 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.
• Conclusions

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Role of anomalous perceptual experience in the
psychosis continuum

• Multiple contributory factors have been proposed,
  but are largely unidentified (Johns and 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?
• Focus on hallucinatory experience, excluding
  changes in intensity, sensory flooding etc
• Ignore anomalies associated with temporal lobe
  disturbance.

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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
Bell et al. (2006)

• 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 20




diff by at least p lt 0.0005 on two-tailed
t-test from nonclinical
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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 relevant experiences from
  the non-clinical TL literature.

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TL Factor Validation

• Work by Caroline Dietrich
• Standard linear regression, N39
• DV TL Scale (Markarec and Persinger, 1985)
• IVs CAPS Factors minus identical shared items.

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TL Factor Validation

• However, this is purely correlative and we wanted
  to look at the causative role of the temporal
  cortices in anomalous experience.
• Used a paradigm from Brugger et al. (1993)

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TMS Study
Detect the hidden pictures
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Bell et al. (in press)

• In reality, all patterns were completely random.
• Brugger et al. (1993) found that healthy
  participants professing a belief in ESP were more
  likely to see meaningful information in visual
  noise.
• We did the same experiment, but controlled for
  schizotypy-like experience in the 12 participants.

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Bell et al. (in press)

• Applied TMS to the vertex, and left and right
  lateral temporal cortices just before stimulus
  onset.
• TMS caused no significant effect on reaction time.

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Effect on detect responses

Sig main effect plt 0.05 Sig diff from left at
p lt 0.05
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Role of Temporal Lobes

• Lack of effect on RT suggests no general
  cognitive slowing or response inhibition.
• Effect on detect responses suggest temporal
  lobe function is involved in anomalous perceptual
  experiences.
• Provides some evidence for validation of TL CAPS
  factor
• and therefore for multiple factors underlying
  anomalous experience continuum.

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Anomalous Experience in Delusions

• Various theories suggest that anomalous
  perceptual experience is necessary for delusion
  formation.
• Many draw on Maher (1974 1988 1999) who argues
  that it is necessary for the presence and content
  of delusions.
• The CAPS allows us to test this in deluded
  patients.

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Comparison with deluded patients
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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CAPS Psychometric Properties

• How does this match up with non-clinical results?

• This suggests delusional ideation and anomalous
  perceptual experience are associated in this
  sample.
• But this is an average relationship, and doesnt
  represent the distribution of the differences.

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Bell et al. (in submission)

• For each participant, calculated the percentage
  diff between
• Delusional ideation (PDI score)
• Anomalous perceptual experience (CAPS score)
• and graphed the distribution.

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CAPS-PDI diff in nonclinical sample
N 337
Low anomalous exp
High anomalous exp
High delusional ideation
Low delusional ideation
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CAPS-PDI diff in psychotic sample
N 20
Low anomalous exp
High anomalous exp
High delusional ideation
Low delusional ideation
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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.
• Anomalous perceptual experience, as measured by
  the CAPS, is not necessary for delusions.
• Relationship between anomalous perceptual
  experience and delusional ideation is normally
  distributed.