What is the Nature of the Perceptual Deficit in Congenital Prosopagnosia?IrvingBiederman1,2*,EshedMargalit2,4,RafaelS.Maarek3,EmilyX.Meschke2,BryanE.Shilowich1,
JordanJ.Juarez2,CatrinaM.Hacker2,TaylorJ.Seamans2,SarahB.Herald51DepartmentofPsychology2NeuroscienceProgram 3DepartmentofBiomedicalEngineering,UniversityofSouthernCalifornia,4NeuroscienceProgram,StanfordUniversity,5DepartmentofPsychologicalandBrainSciences,DartmouthCollege
Image Understanding Lab
Isthereaperceptualdeficitincongenitalprosopagnosia(CP)?Ifso,whatisitsnature?
Thestandardtestsfordiagnosingprosopagnosia,e.g.,CFMT,PI20,Celebrity,etc.,documentdeficitsinfacerecognition,buttheyleaveopenwhetherthedeficitisperceptualasopposedto,forexample,memory.TheBenton,amatch-to-sampletestthathasservedasthestandarddiagnosticinstrumentforalmostthreedecades,allowsthesubjecttoexploitsmalllocalfeatures,e.g.,thepatternofhairsintheeyebrow,thusenablingsomeprosopagnosicstoscorenormallyonthetest(Duchaine&Nakayama,2006).
ReferencesDuchaine,B.,&Nakayama,K.(2006).TheCambridgeFaceMemoryTest....Neuropsychologia,44,576-585.Yue,X.,Tjan,B.S.,&Biederman,I.(2006).Whatmakesfacesspecial?VisionResearch,46,3802-3811.Xu,X.,Biederman,I.,&Shah,M.S.(2014).Aneurocomputational accountofthefaceconfiguraleffect. JournalofVision,14,1-9.
AssessingtheperceptualsensitivityofCPsandControlstosmallmetricdifferencesinFacesandBlobs
Inthesethreetrials,whichofthebottomtwoimagesisanexactmatchtothetopimage?
SimilarityofdistractorsforFacesandBlobswerescaledtobeequallydissimilaraccordingtotheGaborJetmodel.
Sampletrialswithblobstimuli(left)andfacestimuli(right).Subjectswereinstructedtoindicateviabuttonpresswhichofthebottomtwoimageswasanexactmatchtothetopimage.Correctanswer:Left Correctanswer:Left Correctanswer:Right
CONCLUSIONS1. CPsaredeficientintheirperceptualdiscriminationofsmalldifferencesin
complex,smoothlycurved,metrically-varyingstimulisuchasFacesandBlobs.2. Thisdeficitdoesnotextendtothediscriminationofmetricdifferencesofthe
samemagnitudeinsimplegeometricvolumes,suggestingaselectiveimpairmentinthediscriminationofbiologicallyplausiblestimuli.
SPECULATIONThedeficitinmetricdiscriminationofcomplex,biologicallyappearingshapesbyCPsmaybeasymptom ratherthantheunderlyingcauseoffacerecognitiondeficits.Yueetal.(2006)presentedevidencethatFFAretainedthespatial(Gabor-like)tuningcharacteristicofearliervisualstages.Xuetal.(2014)showedthatfaceconfiguraleffectswereproducedbylarger.f.s.whichservedtomagnifytheimpactofsmallmetricdifferences;alocaldifferencewouldaffecttheactivationofkernalswithr.f.s.centeredallovertheface.Thusthecoredeficitincongenitalprosopagnosiamaybeaninabilitytobenefitfromtheconfiguraleffects—withtheirattendantmagnificationofsmalldifferences—producedbylargereceptivefieldsinface-selectiveareas.
Results:
Eventhoughnoinformationwasconveyedbyeitherthepresenceofaheadortheorderingoftheparts,enclosingthepartswithinaheadandhavingthepartsinanormalorderresultedinasignificantreductioninRTs.ThepresenceofaheaddidnotfacilitateRTswhenthefacepartswereinverted.Preliminaryresultsfromtwoprosopagnosicsshownoevidenceoftheseconfiguraleffects—neitherthebenefitofaheadnoranuprightorderoffaceparts.
1. Withuprightparts,embeddingthepartsinaheadreducedRTsby300msec!
2. Invertingtheorderoftheparts(butnotthepartsthemselves),increasedRTsby210msec.
3. Therewasnobenefitofembeddingthepartswithinaheadwhenthepartswereininvertedorder.
4. Accuracyforthefourconditionswashigh(between91-93%)withslightadvantagesforthepresenceofahead(.5%)andanuprightorder(1.5%).
DoCPsshowfaceconfiguraleffects?Wedevisedanodd-man-outtaskthatreflectsconfiguralfaceeffectsbutdoesnotrequireidentificationormatchingofapreviouslylearnedface(whichputsCPsatadisadvantageinthestandardconditionastheyhavedifficultyinstoringfaces).
Subjectsviewedadisplaywiththree“faces,”arrangeddiagonally,witheachfacecomposedofthreefaceparts:eyes,nose,andmouth.Ineachtrial,oneofthefacesdifferedsubtlyintheshapeofone ofitsparts.Thetaskwastodetectwhichfacewasthe“oddmanout”:left,middle,orright.Onhalfthetrials,thethreesetsoffacepartswereeachenclosedwithinahead(absentontheotherhalf).Additionally,onhalfthetrials,thepartswereinthenormaluprightorder(eyesontop)and,ontheotherhalf,inaninvertedorder(withthemouthontop).Theindividualpartsthemselveswereneverinverted.Theconfiguraleffectistakenasanadvantageofenclosingthepartsbytheheadandthepartsbeingintheirnormalordering.
Correctanswer:Middle Correctanswer:RightCorrectanswer:Left Correctanswer:Right
DoCPsshowadeficitwhendiscriminatingmetricdifferencesbetweensimpleshapes(i.e.,geons)?NO
TherewasnodifferencebetweenCPsandControlsindiscriminatingmetricdifferencesbetweengeonsofequalsimilarityasthefacesandblobs.
Controls(lightbluelines)madefewererrorsthanDPs(darkbluelines)ontheFacetrials,p<.001,andontheBlobtrials,p<0.001.
ThehighererrorratesofCPsonbothFacesandBlobssuggestthatthedeficitinDPmaynotbe
restrictedtofaces.
Blobs
Faces
Controls
Controls
CPs
CPs
CPsaredeficientindiscriminatingboth FacesandBlobsNote:Errorbarsaresometimesencompassedwithinthedatapoints.
OrderingofParts
DoesperformanceontheMatch-to-SampleFacetaskcorrelatewithstandardmeasuresofprosopagnosia?
YES.EventhoughtheM2Sfacediscriminationtasklooksnothinglikethestandardtestsforassessingprosopagnosia,thecorrelationswiththesemeasuresareashigh(andtypicallyhigher)thananyothermeasure.
CorrelationsofErrorRatesontheM2SFacetaskwith:PI20: -.61***(df=50)CFMT: .64***(df=52)Faceblind.org: .46***(df=53)DoppelgängerDiscrimination: .65***(df=31)USCIULCelebrityFaces: .51***(df =54)
ItissomewhatremarkablethataminimalMatch-to-Sampletaskfordiscriminatingasmall,metricdifferencebetweentwofaces,withnorequirementsformemoryorviewinvariance,accuratelypredictsresponsestoitemsonthePI20suchas”Anxietyaboutfacerecognitionhasledmetoavoidcertainsocialorprofessionalsituations.”
***=p<.001
CorrectAnswer:Left
AcknowledgmentsSupportedbyNSFBCS0617699andtheDornsifeResearchFund.
[email protected]://geon.usc.edu/
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