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Tracking multiple targets with multifocal attention

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TRENDSinCognitiveSciencesVol.9No.7July2005

Trackingmultipletargetswithmultifocalattention

PatrickCavanaghandGeorgeA.Alvarez

DepartmentofPsychology,HarvardUniversity,33KirklandStreet,Cambridge,MA02138,USA

Attentionallowsustomonitorobjectsorregionsofvisualspaceandselectinformationfromthemforreportorstorage.Classicaltheoriesofattentionassumedasinglefocusofselectionbutmanyeverydayactivities,suchasvideogames,navigatingbusyintersections,orwatchingoverchildrenataswimmingpool,http://www.wendangxiazai.comboratorytrackingtaskshaveindeeddemonstratedtheabilitytotrackfourormoretargetssimultaneously.Althoughthemechanismsbywhichattentionmaintainscontactwithseveraltargetsarenotyetestablished,recentstudieshaveidenti edseveralcharacteristicsofthetrackingprocess,includingpropertiesde ninga‘trackable’target,themaximumnumberoftargetsthatcanbetracked,andthehemi eldindependenceofthetrackingprocess.Thisresearchalsohasimplicationsforcom-putervision,wherethereisagrowingdemandformultiple-objecttracking.

Multipletargettrackinghasbecomeaveryactiveareaofresearchnotonlyinhumanvisionbutalsoincomputervisionwherethereisagrowingdemandfortrackingvehiclesfromsurveillancecameras,peopleinairports,andinteractionsbetweenpeopletoinfertheiractivities[1,2].Todate,thereislittleinterchangebetweenthesetwolinesofresearchbutfutureadvancesshouldbringthetwoareasintogreatercontact.

Trackingbyhumansreliescriticallyonattention[3,4]but,classically,visualattentionselectsinformationfromonlyonelocation[5–10],actinglikeasecondfoveathatroamsthevisual eldindependentlyofeyemovements.In1988,PylyshynandStorm[11]convincinglyoverturnedthissinglefocusviewbydemonstratingcontinuoustrackingofmultipletargets(alsoseeBox1).Theirexperimentsusedarraysofidenticalitemsthatmovedwithinarectangulararea,bouncingoffthebordersandeachother.Atthebeginningofatrial,someoftheitemsweremarkedbrie yasthetargetsandtheythenrevertedtobeingidenticaltotheotheritems(Figure1).Allitemsthenmovedrandomlywithinthetargetareaforthenext7–15s.Tomeasureperformanceattheendofthetrial,asingleitemwasprobedandobserversreportedwhetherornotitwasatargetitem.Mostsubjectswereabletokeeptrackofasmanyas4or5targetsoverseveralseconds.Subjectscouldnotuseeyemovementsalonetofollowthesemultipletargets.Norcouldasinglefocusof

Correspondingauthor:Cavanagh,P.(patrick@wjh.harvard.edu).Availableonline13June2005

attentionselectabroadregioncontainingthetargetswithoutalsopickingupthedistractorsinthatregion.Subjectwereperformingasifmorethanonefocusofattentionwereavailable,onetofolloweachtarget(Figure2).

Modelsofmultiple-objecttracking

Severalmodelsformultiple-objecttrackinghaveproposedsincePylyshynandStorm rstreportedtheirresultsand veofthesearedescribedbrie yhere:grouping,attentionswitching,multifocalattention,preattentiveindexes(FINSTs),andobject les(see[12]foramoredetailedreviewofthesemodels).Thegroupingandswitchingproposalsrequireonlyasinglefocusofattention.Yantis[3],forexample,suggestedthatallthetargetsaregroupedintoonehigherorderobjectwitheachtargetavertexinavirtualpolygon.Trackingthisonechangingshapewouldthenrequireonlyasingleattentionalchannel.Whentargetssharesomecommonmotion[3],theygroupmorestronglyandtrackingbecomeseasier.Thisdemonstratesthatredundancyinthetargetscanbeexploitedbytheobserverbutitisnotevidencethatgroupingisthemechanismoftrackingforindependentlymovingtargets.Aswitchingmodel[3,11,12]alsorequiresonlyonefocusofattentionbutitmustcyclerapidlythroughthetargets,indexingtheirlocationsandreturningtoeachbeforeitmovestoofaraway.Asattentionrevisitseachremem-beredlocation,thenearestitemwouldbetakenasthe

Tracking multiple targets with multifocal attention

Tracking multiple targets with multifocal attention

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Tracking multiple targets with multifocal attention

http://www.wendangxiazai.com1364-6613/$-seefrontmatterQ2005ElsevierLtd.Allrightsreserved.doi:10.1016/j.tics.2005.05.009

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