Anomalous Perceptual Experience: - PowerPoint PPT Presentation

1 / 33
About This Presentation
Title:

Anomalous Perceptual Experience:

Description:

Often described as a distribution of psychotic phenomena, that becomes ... Additional data from Nichola Smedley and Emmanuelle Peters ... – PowerPoint PPT presentation

Number of Views:56
Avg rating:3.0/5.0
Slides: 34
Provided by: a1569
Category:

less

Transcript and Presenter's Notes

Title: Anomalous Perceptual Experience:


1
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
2
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

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 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.

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 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

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.

8
(No Transcript)
9
(No Transcript)
10
CAPS Psychometric Properties
  • Reliability
  • Internal a 0.87
  • Test-retest 0.77 0.79
  • Convergent validity (non-clinical sample)

11
Criterion and Discriminant Validity
N 337
N 20




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

17
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.

18
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)

19
Demo here
20
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.

21
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.

22
Effect on detect responses

Sig main effect plt 0.05 Sig diff from left at
p lt 0.05
23
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.

24
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.

25
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
26
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.

27
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.

28
CAPS-PDI diff in nonclinical sample
N 337
Low anomalous exp
High anomalous exp
High delusional ideation
Low delusional ideation
29
CAPS-PDI diff in psychotic sample
N 20
Low anomalous exp
High anomalous exp
High delusional ideation
Low delusional ideation
30
Bell et al. (in submission)
  • What is the relationship between difference in
    delusional ideation and anomalous perceptual
    experience and perceived distress?

31
Relationship to Distress
Low anomalous exp
High anomalous exp
High delusional ideation
Low delusional ideation
32
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.

33
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.
Write a Comment
User Comments (0)
About PowerShow.com