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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