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Temporal integration of visual stimuli in
schizophrenic patients
Cathleen Schütze, Jennifer Meschke, Manfred Fahle
Andreas Brand 6th Conference on Cognitive
Neuropsychiatry Bremen 2006
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Introduction Hypotheses Methods Results
Discussion
Schizophrenic patients ? Have perceptual deficits
(besides cognitive) ? These deficits already
exist in early visual processing ? E.g. patients
perform worse than controls in visual backward
masking tasks (Slaghuis 2004, Herzog et al.
2004) ? The deficit is attributed to dysfunction
of the transient visual pathway (Butler
Javitt, 2005)
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Introduction Hypotheses Methods Results
Discussion
Backward masking deficit in schizophrenic patients
Mask 300ms
Stimulus Onset Asynchrony
vernier
time
Performance good ? short SOA poor ? long SOA
Herzog et al. 2004
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Introduction Hypotheses Methods Results
Discussion
Temporal Integration Task
PERCEPT
frame 2
Performance good ? Integration over long ISI poor
? Integration over short ISI
Inter Stimulus Interval
time
frame 1
Hogben DiLollo 1974
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Introduction Hypotheses Methods Results
Discussion
Question
? What occurs to the early visual deficit in
schizophrenic patients if they have to integrate
two briefly presented stimuli ? ? Are patients
with prolonged Stimulus Onset Asynchronies (SOAs)
in backward masking task able to integrate two
briefly presented stimuli over a longer time
interval ?
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Introduction Hypotheses Methods Results
Discussion

• Psychophysical measurement of thresholds
• Masking experiment - Determination of SOA
  (Stimulus Onset Asynchrony)
• Constant individual vernier duration
• Constant vernier offset of 70 (arcsec)
• 2x 2AFC, 80 Trials
• Staircase over SOA, starting at 200ms
• Target threshold 75 correct responses
• Temporal integration of brief visual stimuli
  Determination of ISI (Inter Stimulus Interval)
• 2x 2AFC, 80 trials
• Staircase over ISI, starting at 0ms
• Target threshold 75 correct responses
• Neuropsychological Assessment
• D2-test (attention)
• LPS 3 (reasoning)
• MWT-A (premorbid intelligence)

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Introduction Hypotheses Methods Results
Discussion
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Introduction Hypotheses Methods Results
Discussion

• Psychophysical measurement of thresholds
• Masking experiment - Determination of SOA
  (Stimulus Onset Asynchrony)
• Constant individual vernier duration
• Constant vernier offset of 70 (arcsec)
• 2x 2AFC, 80 Trials
• Staircase over SOA, starting at 200ms
• Target threshold 75 correct responses
• Temporal integration of brief visual stimuli
  Determination of ISI (Inter Stimulus Interval)
• 2x 2AFC, 80 trials
• Staircase over ISI, starting at 0ms
• Target threshold 75 correct responses
• Neuropsychological Assessment
• D2-test (attention)
• LPS 3 (reasoning)
• MWT-A (premorbid intelligence)

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Introduction Hypotheses Methods Results
Discussion
Vernier offset ?
right
left
Press button
RESPONSE
mask
blank screen
Dependent variable threshold SOA
vernier
time

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Introduction Hypotheses Methods Results
Discussion

• Psychophysical measurement of thresholds
• Masking experiment - Determination of SOA
  (Stimulus Onset Asynchrony)
• Constant individual vernier duration
• Constant vernier offset of 70 (arcsec)
• 2x 2AFC, 80 Trials
• Staircase over SOA, starting at 200ms
• Target threshold 75 correct responses
• Temporal integration of brief visual stimuli
  Determination of ISI (Inter Stimulus Interval)
• 2x 2AFC, 80 trials
• Staircase over ISI, starting at 0ms
• Target threshold 75 correct responses
• Neuropsychological Assessment
• D2-test (attention)
• LPS 3 (reasoning)
• MWT-A (premorbid intelligence)

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Introduction Hypotheses Methods Results
Discussion
RESPONSE
Missing Dot ?
13ms ? frame 2
blank screen ? Inter Stimulus Interval
right
left
time
13ms ? frame 1
Press button
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Introduction Hypotheses Methods Results
Discussion
Example for Inter Stimulus Interval 0ms
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Introduction Hypotheses Methods Results
Discussion
Example for Inter Stimulus Interval 150ms
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Introduction Hypotheses Methods Results
Discussion

• Psychophysical measurement of thresholds
• Masking experiment - Determination of SOA
  (Stimulus Onset Asynchrony)
• Constant individual vernier duration
• Constant vernier offset of 70 (arcsec)
• 2x 2AFC, 80 Trials
• Staircase over SOA, starting at 200ms
• Target threshold 75 correct responses
• Temporal integration of brief visual stimuli
  Determination of ISI (Inter Stimulus Interval)
• 2x 2AFC, 80 trials
• Staircase over ISI, starting at 0ms
• Target threshold 75 correct responses
• Neuropsychological Assessment
• D2-test (attention)
• LPS 3 (reasoning)
• MWT-A (premorbid intelligence)

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Introduction Hypotheses Methods Results
Discussion

• Inclusion Criteria
• Diagnosis of schizophrenia according to DSM-IV
• Signed informed consent (Declaration of Helsinki)
• Exclusion Criteria
• Recent substance abuse
• Diagnosis of neurological disease
• Binocular visual acuity less than 0.9

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Introduction Hypotheses Methods Results
Discussion
Demographical and neuropsychological data of
participants
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Introduction Hypotheses Methods Results
Discussion
Backward Masking
p lt .01
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Introduction Hypotheses Methods Results
Discussion
Correlations (Spearman Rho) Controls r -
.17 p .57
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Introduction Hypotheses Methods Results
Discussion
Correlations (Spearman Rho) Controls r -
.17 p .57 Patients
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Introduction Hypotheses Methods Results
Discussion
Correlations (Spearman Rho) Controls r -
.17 p .57 Patients r - .59 p lt .05
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Introduction Hypotheses Methods Results
Discussion

• Schizophrenic patients need longer SOAs in
  backward masking compared to controls
• Schizophrenic patients tendentially can integrate
  two briefly presented stimuli only with shorter
  ISIs than controls
• No correlation between temporal integration and
  backward masking thresholds in healthy controls
• Negative correlation between temporal integration
  and backward masking thresholds in schizophrenic
  patients
• Use of sustained information (or perceptual
  persistence) is impaired in schizophrenic patients

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Thank you for your attention
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Introduction Hypotheses Methods Results
Discussion
? Masking means the temporal segregation of two
briefly presented stimuli ? What happens with the
temporal deficit in schizophrenic patients if
they have to integrate two briefly presented
stimuli ? ? Are patients with prolonged Stimulus
Onset Asynchronies (SOAs) in backward masking
task able to integrate two briefly presented
stimuli over a longer time interval ?
Temporal Integration (integrated ISI)
0
Backward masking (SOA)
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Introduction Hypotheses Methods Results
Discussion

• Determination of visual acuity (Freiburger
  Visustest)
• Determination of vernier duration (individually)
• Constant vernier offset of 46 (arcsec)
• 2AFC, 80 Trials
• Staircase over vernier duration, starting at
  150ms
• Masking Experiment - Determination of SOA
  (Stimulus Onset Asynchrony)
• Constant individual vernier duration
• Constant vernier offset of 70
• 2x 2AFC, 80 Trials
• Staircase over SOA, staring at 200ms
• Control Experiment
• Constant individual vernier duration and constant
  individual SOA
• 2AFC, 80 Trials
• Staircase over vernier offset, starting at 150
• Temporal integration of brief visual stimuli
• 2AFC, 80 trials

dependent threshold duration ?
temporal dependent threshold SOA ?
temporal dependent threshold vernier
offset ? spatial (expected 70) dependent
threshold ISI ? temporal dependent
variables T-Value