Anomalous Perceptual Experience:

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Anomalous Perceptual Experience
Underlying Factors and Links to Delusions
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.
• Link to delusions and distress.
• 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 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?
• 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 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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Demo here
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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
• One-stage theories (Maher, 1974 1999)
• Two-stage theories (Ellis and Young, 1990
  Langdon and Coltheart, 2000)
• 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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Bell et al. (in submission)

• What is the relationship between difference in
  delusional ideation and anomalous perceptual
  experience and perceived distress?

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Relationship to Distress
Low anomalous exp
High anomalous exp
High delusional ideation
Low delusional ideation
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Bell et al. (in submission)

• This suggests delusional ideation may be
  protective in people with high levels of
  anomalous perceptual experience.
• But further work needs to be completed to
  understand which aspects of this are beneficial
  or compensatory.

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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 is not necessary
  for delusions.
• Relationship between anomalous perceptual
  experience and delusional ideation is normally
  distributed and linked to distress.