Experiment Design 4: Theoretical + Operational Def’ns Martin Ch. 7

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

Measure Reliability vs. Validity n Valid, reliable n Valid, not reliable n Not valid, reliable n Not valid, not reliable

Reliability n Test-retest –Same score again? n Alternative-form –Same score on similar test? n Split-half –Same score on even and odd items? n Inter-rater –Same score assigned by different raters?

Construct (measure) validity n Face –Sounds plausible on the face of it? n Content –Content details seem appropriate? n Predictive –Predicts things that it should predict? n Concurrent –Correlated with things that should be related? (but not too highly!)

Example experiments n Intelligence & age n Classroom size & learning

Indirect measures: Behavioral measures n Reaction time –More time = more processing or less automatic –Need large N to get reliable data n Choice & errors –Harder = more processing or less automatic n Speed-accuracy tradeoffs

Even more indirect measures: Physiological measures n Examples: –GSR, EEG, PET, fMRI, MEG n Timing: –Timing of activation = timing of processing n Activity: –More activation = more processing

Direct stimulation n Apply small electrical charge to brain area n Ask patient what happens –See lights or hear sounds, etc?

n Computerized tomography (CT scan) –See brain regions (no timing info) n Positron Emission Tomography (PET) –Track heightened brain flow activity using radioactive isotope (slow timing info) n Functional Magnetic Resonance Imaging (fMRI) –Track magnetic changes due to changes in blood oxygen levels (good timing info) n 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 n Very loud and produces claustrophobia –Therefore, also some questions of poor external validity

An example fMRI study n 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) n Fast changes in EEG in response to a stimulus

Hot off the presses: rTMS n 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 n Lesions –Can establish causality n Direct stimulation –Can establish causality –Excellent localization n Imaging –Study normal functions –Good localization and/or timing info n rTMS –Can establish causality –Damage temporary Con n Lesions –Normal patients? –Poor localization n Direct stimulation –Damage cells? –Bigger patterns? n Imaging –Causal? –Subtractive logic? n rTMS –Seizures? –Poor timing information –Localization not clear