experiment design 4: theoretical + operational def’ns
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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
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