experimental design - university of · pdf fileexperimental design butterfly categorical...

ExperimentalExperimental DesignDesign

Thomas WolbersThomas WolbersSpace and Aging LaboratorySpace and Aging LaboratoryCentre for Cognitive and Neural SystemsCentre for Cognitive and Neural Systems

SPM Course Edinburgh 2010

Design Design of functional neuroimaging studiesof functional neuroimaging studiesCategoricalCategorical designsdesignsFactorialFactorial designsdesignsParametricParametric designsdesignsfMRIfMRI adaptationadaptationControl conditionsControl conditionsTrial timingTrial timing

Overview

SPM Course Edinburgh 2010Categorical Designs

F.C. Donders

Subtraction logicSubtraction logic in in psychophysicspsychophysicsAssumption of pure insertion:Assumption of pure insertion:⇒⇒ you can insert a component process into a task without you can insert a component process into a task without

disrupting the other componentsdisrupting the other components⇒⇒ you can estimate duration of a cognitive process by you can estimate duration of a cognitive process by

comparing reaction times between different conditionscomparing reaction times between different conditions


DetectStimulus

PressButton

DetectStimulus

PressButton

Discriminate Color

DetectStimulus

PressButton

Discriminate Color

ChooseButton

T3: Choice Reaction Time• Hit left button when light is green and right button when light is red

T1: Simple Reaction Time• Hit button when you see a light

T2: Discrimination Reaction Time• Hit button when light is green but not red


DetectStimulus

PressButtonT1

DetectStimulus

PressButton

Discriminate ColorT2

-

Discriminate Color

=


DetectStimulus

PressButton

Discriminate ColorT2

-

=

DetectStimulus

PressButton

Discriminate Color

ChooseButtonT3

ChooseButton


BackgroundBackground⇒⇒ pure insertion: you can insert a component process into a task pure insertion: you can insert a component process into a task

without disrupting the other componentswithout disrupting the other components⇒⇒ addtional cognitiveaddtional cognitive processesprocesses always evoke the same additional always evoke the same additional

activation!activation!⇒⇒ activation due to baselineactivation due to baseline task task unaffected!unaffected!

moving dotsmoving dots fixationfixation

SimpleSimple subtractionsubtraction•• you can identify functionally specialised regions with regionallyou can identify functionally specialised regions with regionally y

specific activation differencesspecific activation differences

Categorical Designs


SerialSerial subtractionsubtractionQuestion:Question: Is inferiorIs inferior temporaltemporal cortexcortex (IT) (IT) involvedinvolved in in phonological retrieval phonological retrieval during object recognition?during object recognition?

CognitiveCognitive processesprocesses

⇒⇒ visualvisual analysis:analysis: occipitaloccipital cortexcortex

⇒⇒ object recognition:object recognition: ??????

⇒⇒ phonologicalphonological retrieval:retrieval: ??????

⇒⇒ verbalverbal outputoutput: : BrocaBroca‘‘s areas area

Categorical Designs


A A say say „„yesyes““ when you see an abstract imagewhen you see an abstract image((vis. vis. analysis,analysis, verbal outputverbal output)) ⇒⇒ yesyes

B B say say „„yesyes““ when you see a concrete when you see a concrete objectobject

((vis. vis. analysis,analysis, object recognition, verbalobject recognition, verbaloutputoutput))

⇒⇒ yesyes

C C namename concreteconcrete objectobject((vis. analysis, object recognition, vis. analysis, object recognition, phonological retrieval, verbal outputphonological retrieval, verbal output))

⇒⇒

ExperimentalExperimental designdesign

butterflybutterfly

Categorical Designs


visual analysisobject recognitionphonological retrievalphonological retrievalverbal output

Problem:Problem: unjustified assumption that IT response to object recognition isunjustified assumption that IT response to object recognition iscontext independentcontext independent!!

psychophysicspsychophysics ≠≠ neurophysiologyneurophysiology

visual analysisverbal output

visual analysisobject recognitionverbal output

-------------------AA

⇒⇒ significantsignificant IT activationIT activation ⇒⇒ object recognition!object recognition!B B -- AA

⇒⇒ nono significant ITsignificant IT activationactivation ⇒⇒ no evidence for IT no evidence for IT involvement in phonological retrieval!involvement in phonological retrieval!

C C -- BB

visual analysisobject recognitionobject recognitionverbal output


BB CC

Categorical Designs


A B C D task

interaction terminteraction term(task B x task D)(task B x task D)

C C -- DD = - =

- =

-

=interactioninteraction

BackgroundBackground•• ““the whole is more than just the sum of its partsthe whole is more than just the sum of its parts””•• cognitive processes are interdependent cognitive processes are interdependent ⇒⇒ task A interacts with task B, task A interacts with task B,

A modulates sensitivity to B ... A modulates sensitivity to B ...

B B -- AA =

Factorial Designs



•• phonological retrieval modulatesphonological retrieval modulates IT response to object recognitionIT response to object recognition⇒⇒ IT IT also involvedalso involved in in phonological retrieval!phonological retrieval!

no object no object recogn.recogn.

D D Name colour of abstract imageName colour of abstract image((vis. vis. analysis,analysis, phonological retrieval,phonological retrieval, verbal verbal outputoutput))

⇒⇒ greengreen

phonolog. phonolog. retrievalretrievalnono phonolog. phonolog. retrievalretrieval

(C (C -- D) D) –– ⇒ significant IT activation(B (B -- A)A)

visual analysisverbal output

visual analysisobject recognitionverbal output

AA

BB CC

visual analysisphonological retrievalphonological retrievalverbal output

DD

object object recognit.recognit.

visual analysisobject recognitionobject recognitionverbal output

Factorial Designs

Interaction:



Example 1Example 1: : linear activation linear activation increase inincrease in LOC LOC with increasing with increasing object visibility!object visibility!

SystematicSystematic variationvariation of regionalof regional activation withactivation with endoendo--/exogenous/exogenous parametersparameters⇒⇒ task stays the same while the amount of processing varies; thus,task stays the same while the amount of processing varies; thus, changes to changes to

the nature of the task are less of a problem the nature of the task are less of a problem ⇒⇒ you can test for bothyou can test for both linearlinear (i.e.level(i.e.level of sensorimotor/cognitive processing)of sensorimotor/cognitive processing) andand

nonnon--linear effectslinear effects (i.e. time effects)(i.e. time effects)

categorical/factorialcategorical/factorial designsdesigns

cognitivecognitive processesprocesses

parametricparametric designsdesigns

binarybinary

continuouscontinuousS

igna

l

object visibilityobject visibility

Parametric Designs

RoseRose et al. et al. (2005).(2005). Cerebral Cerebral CortexCortex..


1 2 3 4 5

Sig

nal ExampleExample 2: 2: NonNon--linearlinear decrease ofdecrease of prefrontal prefrontal

activation over time during procedural learning!activation over time during procedural learning!

Combining parametricCombining parametric andand factorialfactorial designsdesignsnonnon--linear interactionlinear interactionlinear interactionlinear interaction

V1V1

STSSTS

visibilityvisibility

Sig

nal

Sig

nal1-back

2-back

Sig

nal

object visibilityobject visibility RainerRainer et al. (2001). et al. (2001). CurrentCurrentBiologyBiology..

Parametric Designs

SPM Course Edinburgh 2010fMRI Adaptation

HensonHenson et al. (2000)et al. (2000)

FusiformFusiform gyrusgyrus

repetition suppression / fMRI adaptation / primingrepetition suppression / fMRI adaptation / priming

fMRI adaptationfMRI adaptationpriming = reduced BOLD response to primed stimuli (i.e. priming = reduced BOLD response to primed stimuli (i.e. repeated presentation)repeated presentation)


120°90°60° 150°

tuning curvefor this one neuron

Viewing angle

Neu

rona

l act

ivity

monkeymonkey STSSTS

Priming as a toolPriming as a toolincrease in spatial resolution (increase in spatial resolution (hyperresolutionhyperresolution))example: orientation tuning for face stimuliexample: orientation tuning for face stimuli

⇒⇒ viewpoint selectivity in the human FFA?viewpoint selectivity in the human FFA?


Priming as a toolPriming as a toolfMRI fMRI –– voxel typically contain ten thousands of neuronsvoxel typically contain ten thousands of neuronsFFA: mixture of neurons tuned to different orientations?FFA: mixture of neurons tuned to different orientations?

120°90°

60°150°

180°

Viewing angle

Neu

rona

l act

ivity

30°0°

-30°-60°

Tuning curvesfor three different neurons

identical BOLD response to identical BOLD response to each orientation!each orientation!

Slide modified from Jody Culham


‘‘samesame’’stimulistimuli

‘‘differentdifferent’’StimuliStimuli

predicted BOLD-responses

Slide modified from Jody Culham

fMRI Adaptation

orientation tuning in the humanorientation tuning in the human FFA?FFA?


GrillGrill--SpectorSpector & & MalachMalach (2001), Acta (2001), Acta PsycholPsychol..

facesfaces vs. vs. objectsobjects fMRIfMRI adaptationadaptation

orientation tuning in the humanorientation tuning in the human FFA?FFA?

SPM Course Edinburgh 2010Control Condition

ProblemProblem•• fMRI = fMRI = contrastivecontrastive methodmethod

⇒⇒ for many designs, you need to include adequatefor many designs, you need to include adequate control conditionscontrol conditions

„„RestRest““ = = often substantial activation in many areas!often substantial activation in many areas!⇒⇒ reason:reason: mentalmental imageryimagery / rehearsal / / rehearsal / eye movementseye movements……⇒⇒ lossloss ofof sensitivity!sensitivity!

Stark & Squire (2001) Stark & Squire (2001) –– When When zero is not zero... zero is not zero... PNASPNAS, , 98(22), 1276098(22), 12760--12766.12766.

SPM Course Edinburgh 2010Control Condition

⇒⇒ decision depends on experimentaldecision depends on experimental hypotheses!hypotheses!

AlternativesAlternatives1.1. high congruency withhigh congruency with experimental conditionsexperimental conditions2.2. additional possibilities:additional possibilities:

Stark & Squire (2001) Stark & Squire (2001) –– When When zero is not zero... zero is not zero... PNASPNAS, , 98(22), 1276098(22), 12760--12766.12766.


analysis of entire block, not of single analysis of entire block, not of single stimulistimulilarge effectslarge effectsOptimal block length: ~16secOptimal block length: ~16sec

⇒⇒ allows enough time for signal to allows enough time for signal to oscillate fullyoscillate fully

⇒⇒ not near artifact frequenciesnot near artifact frequencies

analysis of single stimulianalysis of single stimulismaller effectssmaller effectsminimal SOA: ~2secminimal SOA: ~2sec

Block DesignBlock Design EventEvent--Related DesignRelated Design

Trial timing

Stimulus trainStimulus train

Hypothetical BOLD responseHypothetical BOLD response

Stimulus trainStimulus train

Hypothetical BOLD responseHypothetical BOLD response

SPM Course Edinburgh 2010Trial timing

Advantages of eventAdvantages of event--related designrelated designrandomised order avoids unwanted psychological effectsrandomised order avoids unwanted psychological effects

e.g. habituation / expectancy effects, attentional e.g. habituation / expectancy effects, attentional declinedecline


RandomisedRandomised

O1 N1 O3O2 N2

DataData

ModelModel

O = Old WordsO = Old WordsN = New WordsN = New Words

BlockedBlocked

O1 O2 O3 N1 N2 N3

Trial timing

Slide modified from Rik Henson



e.g. habituation / expectancy effects, attentional e.g. habituation / expectancy effects, attentional declinedecline

postpost--hoc/subjective classification of trials hoc/subjective classification of trials e.g. subsequent memory effecte.g. subsequent memory effect


R R RF F

R = Words Later RememberedR = Words Later RememberedFF = Words Later Forgotten= Words Later Forgotten

~4s

DataModel

EventEvent--relatedrelated

Trial timing




e.g. habituation and expectancy effects, attentional e.g. habituation and expectancy effects, attentional declinedecline


some events can only be indicated by subject (in time)some events can only be indicated by subject (in time)e.g. spontaneous perceptual changese.g. spontaneous perceptual changes


0 5 10 15 200

5

10

15

20

Inter−Reversal Time (s)

Num

ber o

f Per

cept

ual R

ever

sals

0 5 10 15 200

5

10

15

20

25

Inter−Reversal Time (s)

Trial timing




e.g. habituation and expectancy effects, attentional e.g. habituation and expectancy effects, attentional declinedecline


some events can only be indicated by subject (in time)some events can only be indicated by subject (in time)e.g. spontaneous perceptual changese.g. spontaneous perceptual changes

some trials cannot be blockedsome trials cannot be blockede.g. e.g. „„oddballoddball““ paradigmsparadigms


TimeTime…

““OddballOddball””


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