Experimental Design

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Experimental Design
Chloe Hutton The Wellcome Department of Imaging
Neuroscience, London, UK
Slides from Daniel Glaser, Rik Henson, Christian
Buchel, Karl Friston, Chris Frith, Cathy
Price,Ray Dolan The Wellcome Department of
Cognitive Neurology, UCL London UK
http//www.fil.ion.ucl.ac.uk/spm
chutton_at_fil.ion.ucl.ac.uk
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Data transformations
Statistical parametric map (SPM)
Image time-series
Design matrix
Kernel
Realignment
Smoothing
General linear model
Gaussian field theory
Statistical inference
Normalisation
p lt0.05
Template
Parameter estimates
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Stimuli
SPMT

isoluminant stimuli (even)

V5
isochromatic stimuli (odd)
speed
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A taxonomy of design

• Categorical designs
• Subtraction - Pure insertion and cognitive
  subtraction
• - Differential event-related fMRI
• Conjunction - Testing multiple hypotheses
• Parametric designs
• Linear - Cognitive components and dimensions
• Nonlinear - Polynomial expansions and
  neurometric functions
• - Nonlinear event-related fMRI
• Factorial designs
• Categorical - Additive factors and pure
  insertion
• - Psychopharmacological designs
• - Adaptation, modulation and dual-task
  inference
• Parametric - Linear and nonlinear interactions
• - Psychophysiological Interactions

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A categorical analysis
Experimental design Word generation G Word
repetition R R G R G R G R G R G R G
G - R Intrinsic word generation
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Cognitive Conjunctions
Components Object Recognition R Phonological
Retrieval P Visual Processing V Tasks Object
naming R,P,V,RxP Colour naming P,V Object
viewing R,V Colour viewing V The Conjunction
R,V - V R,V,P, RxP - V,P R, RxP
R R
Object recognition responses (R)
viewing naming
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A parametric analysis
The nonlinear effect of time assessed with the
SPMT
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Nonlinear parametric responses
Inverted U response to increasing word
presentation rate in the DLPFC
SPMF
42 wpm
Regression and design matrix
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A factorial analysis
Time x condition interactions (i.e.
adaptation) assessed with the SPMT
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Factorial analysis psychopharmacological study

• PET, 6 subjects, 6 conditions
• 3 x 2 factorial design, Buspirone x Memory

left parahippocampal responses
sub- supra-
pre-
acute-
pre acute post
post-
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Context-sensitive responses
time
stimulus n
stimulus n-1
stimulus n1
interaction between stimuli
response n
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Interactions and context-sensitive effects
A 2 x 2 layout
Context 1 (no naming)
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2
Context 2 (naming)
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3
without A with A (e.g.. recognition)
interaction effect (A x Context)
A
A
task 1 2
3 4
Context 1
Context 2
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Interaction effects in the left inferotemporal
region
A PET study of object naming
Components Visual processing V Object
recognition R Phonological retrieval P Interacti
on RxP Conjunction (name object - shape)
(view object - shape) (R RxP) R
R Interaction (name object - shape) -
(view object - shape) (R RxP) - R
RxP

Object-specific activations
adjusted rCBF
Context no naming naming
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Epoch vs Event-related fMRI
PET Blocked conception (scans assigned to
conditions)
fMRI Epoch conception (scans treated as
timeseries)
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Randomised trial order
c.f. confounds of blocked designs (Johnson et al
1997)
Blocked
Randomised
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Post hoc / subjective classification of
trials e.g, according to subsequent memory
(Wagner et al 1998)
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Some events can only be indicated by subject (in
time) e.g, spontaneous
perceptual changes (Kleinschmidt et al 1998)
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Some trials cannot be blocked e.g, oddball
designs (Clark et al., 2000)
Time
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Differential event-related fMRI
BOLD EPI fMRI at 2T, TR 3.2sec. Words presented
every 16 secs (i) studied words or (ii) new words
Parahippocampal responses to words
SPMF testing for evoked responses
studied words
SPMF testing for differences
new words
Peri-stimulus time secs
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Summary

• Consider how the experiment will be analysed in
  the early stages of experimental design.
• Are your factors of interest context specific?
• Can you express your design parametrically?
• In fMRI should the design be blocked or event
  related? Event-related is more flexible, blocked
  more efficient.