Prof. Greg Francis 1/2/12 PSY 200: Intro. to ... - Purdue University

Prof. Greg Francis 1/2/12DifferencesWe have to look for differences in activityAlzheimer’s patients have reduced brain activityA simple experimentSuppose you run an fMRI experiment where a person alternatesbetween seeing a blank screen and a faceYou take multiple fMRI scans with half recording brain activity duringthe blank and half recording brain activity during the faceAdd them up pixel by pixel for each conditionViewing blankViewing facePurdue UniversityPurdue UniversitySubtraction methodSubtract the fMRI signals produced by one condition from the fMRIsignals produced by another conditionThe difference map indicates those brain regions that are involved inthe different cognitive tasksIt requires a sophisticated statistical analysis to avoid false positives!Viewing blankViewing facePurdue UniversityDifference mapWhat is usuallyreported is just thedifference mapColors mark placesin the brain that arestatistically differentbetween conditions Czisch et al. (2009)for rare tones vs.frequent tonesThe map would bedifferent if itcompared rare tonesversus speechReportingPurdue UniversityFunctional MRIFunctional MRIColor maps showstrongest“responses”e.g., during a taskthat requires covertspatial attentioncompared to one thatdoes not requireattentionWhen moving apointer to a targetbox compared to nomovement “activity” in areasinvolved in vision,planning, and motorcontrolPurdue UniversityPurdue UniversityPSY 200: Intro. to Cognitive Psychology 4