Theoritical & Operational Definitions

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Experiment Design 4:

Theoretical + Operational Def¶ns

Martin Ch. 7



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



Measure Reliability vs. Validity

Valid, r eliable

Valid, not r eliable

Not valid, r eliable

Not valid, not r eliable



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?



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!)



Example experiments

Intelligence & age

Classroom size & learning



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



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



Direct stimulation

Apply small electrical charge to brain

ar ea

Ask patient what happens

± See lights or hear sounds, etc?



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



PET

Images are taken at many different slices

across the brain



An example PET study



An f MR I scanner

Ver y loud and produces claustrophobia ± Ther ef or e, also some questions of poor

external validity



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.



Impose f MR I on top of MR I structural

Use subtractive logic



EEG & ERP



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.



Event-Related Potentials (ERP)

Fast changes in EEG in r esponse to a

stimulus



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



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

Theoritical & Operational Definitions

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