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Experiment Design 4:
Theoretical + Operational Def¶ns
Martin Ch. 7
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Operational Definitions
Select an operational def inition that is:
± Reliable
± Valid
± Likely to produce an effect
± But a lso r epr esentative
± Cost and time effective
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Measure Reliability vs. Validity
Valid, r eliable
Valid, not r eliable
Not valid, r eliable
Not valid, not r eliable
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Reliability
Test-r etest
± Same scor e again?
Alternative-f orm ± Same scor e on similar test?
Split-half
± Same scor e on even and odd items? Inter-rater
± Same scor e assigned by differ ent raters?
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Construct (measure) validity
Face
± Sounds plausible on the f ace of it?
Content ± Content details seem appropriate?
Pr edictive
± Pr edicts things that it should pr edict? Concurr ent
± Corr elated with things that should be
r elated? (but not too highly!)
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Example experiments
Intelligence & age
Classroom size & learning
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Indirect measures:
Behavioral measures Reaction time
± Mor e time = mor e processing or less
automatic
± Need large N to get r eliable data
Choice & errors
± Harder = mor e processing or lessautomatic
Speed-accuracy tradeoff s
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Even more indirect measures:
Physiological measures Examples:
± GSR, EEG, PET, f MRI, MEG
Timing:
± Timing of activation = timing of processing
Activity:
± Mor e activation = mor e processing
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Direct stimulation
Apply small electrical charge to brain
ar ea
Ask patient what happens
± See lights or hear sounds, etc?
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Computerized tomography (CT scan) ± See brain r egions (no timing inf o)
Positron Emission Tomography (PET)
± Track heightened brain flow activity using
radioactive isotope (slow timing inf o)
Functional Magnetic Resonance
Imaging (f MRI)
± Track magnetic changes due to changes
in blood oxygen levels (good timing inf o)
EEG & ERP
± Track brain waves (best timing inf o)
Imaging
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PET
Images are taken at many different slices
across the brain
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An example PET study
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An f MR I scanner
Ver y loud and produces claustrophobia ± Ther ef or e, also some questions of poor
external validity
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An example f MR I study
Subjects viewed a f ace on a computer
monitor f or 3 seconds, held the f ace in
memor y (with no visual stimuli) f or an 8second pause, and then viewed a second
f ace f or 3 seconds. They pr essed a button to
indicate whether or not the f aces matched.
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Impose f MR I on top of MR I structural
Use subtractive logic
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EEG & ERP
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Data gathered from EEG
ALPHAWAVES, brought on by
unfocusing one's attention, have
relatively large amplitude and
moderate frequencies.
BETAWAVES, the result of
heightened mental activity,typically show rapid oscillations
with small amplitudes.
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Event-Related Potentials (ERP)
Fast changes in EEG in r esponse to a
stimulus
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Hot off the presses: rTMS
Repetitive transcranial magnetic stimulation
± Produce a r epeating magnetic disruption in
one ar ea of the brain to temporally disruptits f unction
± Allows f or causal infer ence
± But can cause epileptic seizur es
± Also, don¶t know if have per fect targeting
ability yet
± Also, because it is r epetitive, don¶t have
timing inf ormation
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Pro
Lesions ± Can establish causality
Dir ect stimulation
± Can establish causality
± Excellent localization
Imaging
± Study normal f unctions
± Good localization and/or
timing inf o
r TMS
± Can establish causality
± Damage temporar y
Con
Lesions ± Normal patients?
± Poor localization
Dir ect stimulation
± Damage cells?
± Bigger patterns?
Imaging
± Causal?
± Subtractive logic?
r TMS
± Seizur es?
± Poor timing inf ormation
± Localization not clear