Behavioral/Systems/Cognitive
TheRoleofSpatialAttentionintheSelectionofRealand
IllusoryObjects
Antı´gonaMartinez,1,2DhakshinS.Ramanathan,1JohnJ.Foxe,2DanielC.Javitt,2andStevenA.Hillyard1
1DepartmentofNeurosciences,UniversityofCalifornia,SanDiego,LaJolla,California92093-0608,and2NathanS.KlineInstituteforPsychiatricResearch,
Orangeburg,NewYork10962
Selectiveattentionmaybeflexiblydirectedtowardparticularlocationsinthevisualfield(spatialattention)ortoentireobjectconfigu-
rations(object-basedattention).Akeyquestioniswhetherspatialattentionplaysadirectroleintheselectionofobjects,perhapsby
spreadingitsfacilitatoryinfluencethroughouttheboundariesofanobject.Westudiedtherelationshipbetweenspatialandobject-based
attentioninadesigninwhichsubjectsattendedtobriefoffsetsofonecornerofarealorillusorysquareform.Object-selectiveattention
wasindexedbydifferencesinevent-relatedpotential(ERP)amplitudesandbloodoxygenlevel-dependent(BOLD)activationstounat-
tendedcorneroffsetsinconditionsinwhichtheobjectswereintactversusfragmentedorabsent.Thisdesignensuredthatobject-based
attentioneffectswerenotanartifactofattentionbeingguidedbysimpledirectionalcuessuchasparallellines,whichmayhaveoccurred
inpreviousstudies.Bothspace-basedandobject-basedattentionwereassociatedwithenhancednegativeERPs(N1componentat
140–180ms)thatwerecolocalizedwithBOLDactivationsinlateraloccipitalcortex(LOC).Theseresultsprovidephysiologicalevidence
thatdirectingspatialattentiontoonepartofanobject(whetherrealorillusory)facilitatestheprocessingoftheentireobjectatthelevel
oftheLOCandthuscontributesdirectlytoobject-basedselectiveattention.
Keywords:ERPs;attention;objectattention;fMRI;dipoles;LOC
Introduction
Whenattentionisdirectedtoaspecificlocationinthevisualfield,
thedetectionanddiscriminationofstimuliatthatlocationbe-
comesfasterandmoreaccurate(Wright,1998).Thisspace-based
stimulusselectionhasbeenlikenedtoamoveable“spotlight”that
canfacilitateprocessingofstimuliatrelevantlocations.Thereis
alsoabundantevidencethatattentioncanselectobjectsintheir
entiretyforpreferentialprocessing(Scholl,2001).Criticalevi-
denceforobject-basedattentioncomesfromstudiesbasedona
designbyEglyetal.(1994)inwhichtwoadjacentrectanglesare
presentedandattentioniscuedtooneendofoneoftherectan-
gles.Thegeneralfindingisthatstimulipresentedatuncuedlo-
cationswithinthecuedrectangleareselectedmorerapidlythan
arephysicallyequivalentstimulipresentedwithintheuncued
rectangle(MarinoandScholl,2005).
Severalinvestigatorshaveproposedthatspace-basedatten-
tionplaysanimportantroleinobject-selectiveattention(Vecera
andFarah,1994;Weberetal.,1997;Davisetal.,2000).According
tothisview,spatialattentiondirectedtoonepartofanobject
spreadsthroughoutitsboundariesandstrengthensthesensory
representationoftheentireobject.Insupportofthis“object-
guidedspatial-selectionmechanism,”physiologicalstudiesusingvariantsofthedual-rectangleparadigmofEglyetal.(1994)have
shownthatneuralactivitypatternsassociatedwithspatialand
object-basedattentionhavemuchincommon,asevidencedby
functionalmagneticresonanceimaging(fMRI)(Mu¨llerand
Kleinschmidt,2003)andevent-relatedpotential(ERP)record-
ings(Heetal.,2004;Martinezetal.,2006,2007).
AlthoughtheparadigmofEglyetal.(1994)hasbeenusedin
manystudiesofobject-basedattention,thereisreasontobelieve
thatthe“sameobjectadvantage”observedinthesestudiesmay
not,infact,reflectselectionoftherectangularobjectitself.In-
stead,Avrahami(1999)suggestedthatattentionmaybeguided
fromcuedlocationsalongthedirectionofthelengthwiseparallel
linesoftherectangleratherthanbyitsintegralobjectproperties.
Insupportofthisproposal,acueingadvantagewasfoundfor
distantstimulisituatedwithinarraysofevenlyspacedparallel
linesthatdidnotconstituteenclosedobjects(Avrahami,1999;
MarinoandScholl,2005).Theseresultscallintoquestion
whethertheparadigmofEglyetal.(1994)providesagoodmetric
ofobject-selectiveattention.
Inpreviousstudies(Martinezetal.,2006,2007),weusedfMRI
andERPrecordingsinanEgly-styleparadigmtoshowthatspace-
basedandobject-basedattentionproducedasimilarpatternof
enhancedneuralactivityinthelateraloccipitalcortex(LOC)at
150–180msafterstimulusonset.Thepresentstudyaimedto
determinewhetherthisneuralactivitypatterninLOC,aregion
previouslyimplicatedinobject-recognitionprocesses(Grill-
Spectoretal.,2001),trulyreflectsobject-selectiveattention.Ac-
cordingly,thepresentstimulusdisplayconsistedofsymmetrical
objects(realandillusorysquares)sothatobject-basedattention
couldnotbebasedonsimplestimulusfeaturessuchasparallelReceivedJan.4,2007;revisedApril28,2007;acceptedMay10,2007.ThisworkwassupportedbyNationalEyeInstituteGrantEY016984.TheCartoolsoftwarewasprogrammedbyDenisBrunet(FunctionalBrainMappingLaboratory,Geneva,Switzerland)andissupportedbytheCenterforBio-medicalImagingofGenevaandLausanne,Switzerland.WethankMattMarlowfortechnicalassistance.CorrespondenceshouldbeaddressedtoDr.AntigonaMartinez,DepartmentofNeurosciences–0608,UniversityofCalifornia,SanDiego,9500GilmanDrive,LaJolla,CA92093-0608.E-mail:antigona@ucsd.edu.DOI:10.1523/JNEUROSCI.0031-07.2007Copyright©2007SocietyforNeuroscience0270-6474/07/277963-11$15.00/0TheJournalofNeuroscience,July25,2007•27(30):7963–7973•7963
