Delusion Formation and the Structure of Anomalous Perceptual Experience

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Delusion Formation and the Structure of Anomalous
Perceptual Experience
Formación de Delirios y la Estructura de las
Experiencias Anómalas de Percepción
Vaughan Bell
Departamento de Psiquiatría, Universidad de
Antioquia
Institute of Psychiatry, Kings College London
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Outline

• Theories of anomalous experience and delusions
• The psychosis continuum
• Cardiff Anomalous Perceptions Scale (CAPS)
• Testing the link between anomalous perceptions
  and delusion formation.
• Underlying factors and life span changes.
• Conclusions

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James Tilly Matthews

• 1796, James Tilly Matthews interrupts a speech by
  Lord Liverpool in the Houses of Parliament.
• He is arrested, taken to court claims that
• He is on a top-secret mission to secure peace
  between France and Britain.
• That the authorities were out to stop him.
• He was being attacked by teams of magnetic
  spies using an air loom to control him.
• Declared mad, he is admitted to Bedlam.

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Illustrations of Madness
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The Air Loom
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James Tilly Matthews

• I am brain-connected to a machine that can
  broadcast pictures to my eyes and voices to my
  mind, and I experience being fully controlled
  from head to toe frequently.
• However, the idea that delusions are the result
  of anomalous experiences was first proposed by
  philosopher and physician John Locke in 1689
• and has stayed with us ever since.

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Anomalous Experience in Delusions

• Various theories suggest that anomalous
  perceptual experience is necessary for delusion
  formation
• One-stage theories Anomalous experiences cause
  delusions (Maher, 1974 1999)
• Two-stage theories Anomalous experiences plus
  reasoning impairment causes delusions (Ellis and
  Young, 1990 Langdon and Coltheart, 2000)

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Psychosis Continuum

• Unusual beliefs and experiences are common in the
  general population.
• The more intense or extreme the experiences, the
  more likely you are to be diagnosed with
  psychosis (Johns and van Os, 2001)
• For example, 10 of the general population score
  above the mean of psychotic inpatients on a
  measure of delusional ideation (Peters et al.,
  2004).
• 10 - 15 people report experiencing
  hallucinations (Tien, 1991)

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How Can We Explain the Psychosis Continuum?

• Research suggests there are many factors, but
  they are largely unidentified (Johns and van Os,
  2001).
• We were interested in identifying some of the
  factors underlying anomalous perceptual
  experience and delusions
• 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

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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 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

• Non-clinical sample N336 mean age 21.6 SD
  5.4
• Reliability
• Internal a 0.87
• Test-retest 0.77 0.79
• Convergent validity

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Criterion and Discriminant Validity
N 336
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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Bell et al. (2008)
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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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

• 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)
• Demo Here

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Bell et al. (2007)

• In reality, all patterns were completely random.
• Brugger et al. (1993) found that healthy
  participants who believe in telepathy were more
  likely to see meaningful information in visual
  noise.
• We did the same experiment, but controlled for
  anomalous experience in the 12 participants.

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Bell et al. (2007)

• Used transcranial magnetic stimulation on the
  vertex, left and right lateral temporal cortices
  before stimulus.
• 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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Bell et al. (in prep)

• 193 members of the general public taken from a
  community survey of residents of South East
  London
• Ages 18 77 (mean 37.5 SD 13.3)
• IQ 69 133 (mean 104.8 SD 12.0)
• Socioeconomic class 1-9 (mean 4.8 SD 2.8)
• No link between CAPS score and illicit drug use
  in the last month (r 0.04 p 0.56),
  suggesting people can distinguish experiences.

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Bell et al. (in prep)

• Correlation with emotion measures (all p lt 0.001)

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Criterion and Discriminant Validity
N 193
N 30




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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Relationship to Paranoid Ideation

• CAPS recently used in a study of paranoid
  thinking in a virtual reality environment.

• CAPS score predicts paranoid reaction to virtual
  reality characters in the general population
  (Freeman et al., 2008a)

• And distinguishes paranoia from social anxiety
  (Freeman et al., 2008b) along with anxiety, worry
  and cognitive inflexibility.

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Bell et al. (in prep)

• Interestingly, no overall correlation with age (r
  -0.078 p 0.284) but differing factor
  structures.
• Median split at age 36 and re-run three factor
  PCA with direct Oblimin rotation.
• The Under 36 sample shows an almost identical
  factor structure to our original sample
• with clear clinical psychosis,
  chemosensation and temporal lobe factors.

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Bell et al. (in prep)

• However, the 36 and Over sample shows a three
  factor solution but a very different picture.
• Interestingly, the first clinical psychosis
  factor is stable.
• But the other two are a mix of all the other
  types of experience.
• Suggesting that the structure of anomalous
  perceptual experience changes throughout life.

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Age-related changes

• Temporal lobe epilepsy patients show age-related
  changes in seizure presentation (Fogarasi et al.,
  2007)
• Late onset psychosis shows a different pattern of
  presentation (Hassett et al., 2005)
• more females than males, virtually no genetic
  loading, strongly associated with cog.
  impairment, and age-specific delusions.
• Such as the partition delusions and the
  phantom boarder delusions

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Conclusions

• The CAPS is a valid, reliable scale for measuring
  anomalous perceptual experience.
• Anomalous perceptual experience as measured by
  the CAPS is not necessary for delusions.
• There may be a number of factors underlying the
  psychosis continuum.
• Temporal lobe disturbance is a likely candidate
  for one of the factors in younger people.
• In older people, there is a marked difference,
  suggesting lifespan changes in the structure of
  anomalous perceptual experience.

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Collaborators
Very many thanks to Peter Halligan Hadyn
Ellis Daniel Freeman Katherine Pugh Emmanuelle
Peters Nicola Smedley Caroline Dietrich