Experiment Design 4:Theoretical + Operational Def’ns

Martin Ch. 7

Operational Definitions

Select an operational definition that is:– Reliable– Valid– Likely to produce an effect– But also representative– Cost and time effective

Measure Reliability vs. Validity

Valid, reliable

Valid, not reliable

Not valid, reliable

Not valid, not reliable

Reliability Test-retest

– Same score again? Alternative-form

– Same score on similar test? Split-half

– Same score on even and odd items? Inter-rater

– Same score assigned by different raters?

Construct (measure) validity

Face– Sounds plausible on the face of it?

Content– Content details seem appropriate?

Predictive– Predicts things that it should predict?

Concurrent– Correlated with things that should be

related? (but not too highly!)

Example experiments

Intelligence & age Classroom size & learning

Indirect measures:Behavioral measures Reaction time

– More time = more processing or less automatic

– Need large N to get reliable data Choice & errors

– Harder = more processing or less automatic

Speed-accuracy tradeoffs

Even more indirect measures: Physiological measures Examples:

– GSR, EEG, PET, fMRI, MEG Timing:

– Timing of activation = timing of processing Activity:

– More activation = more processing

Direct stimulation

Apply small electrical charge to brain area

Ask patient what happens– See lights or hear sounds, etc?

Computerized tomography (CT scan)– See brain regions (no timing info)

Positron Emission Tomography (PET)– Track heightened brain flow activity using

radioactive isotope (slow timing info) Functional Magnetic Resonance

Imaging (fMRI)– Track magnetic changes due to changes

in blood oxygen levels (good timing info) EEG & ERP

– Track brain waves (best timing info)

Imaging

PET

Images are taken at many different slices across the brain

An example PET study

An fMRI scanner

Very loud and produces claustrophobia– Therefore, also some questions of poor

external validity

An example fMRI study

Subjects viewed a face on a computer monitor for 3 seconds, held the face in memory (with no visual stimuli) for an 8 second pause, and then viewed a second face for 3 seconds. They pressed a button to indicate whether or not the faces matched.

• Impose fMRI on top of MRI structural• Use subtractive logic

EEG & ERP

Data gathered from EEG

ALPHA WAVES, brought on by unfocusing one's attention, have relatively large amplitude and moderate frequencies.

BETA WAVES, the result of heightened mental activity, typically show rapid oscillations with small amplitudes.

Event-Related Potentials (ERP) Fast changes in EEG in response to a

stimulus

Hot off the presses: rTMS Repetitive transcranial magnetic

stimulation– Produce a repeating magnetic disruption in

one area of the brain to temporally disrupt its function

– Allows for causal inference– But can cause epileptic seizures– Also, don’t know if have perfect targeting

ability yet– Also, because it is repetitive, don’t have

timing information

Pro Lesions

– Can establish causality

Direct stimulation– Can establish causality– Excellent localization

Imaging– Study normal functions– Good localization and/or

timing info

rTMS– Can establish causality– Damage temporary

Con Lesions

– Normal patients?– Poor localization

Direct stimulation– Damage cells?– Bigger patterns?

Imaging– Causal?– Subtractive logic?

rTMS– Seizures?– Poor timing information– Localization not clear