Impairment of Shooting Performance by Background Complexity and Motion Loïc Caroux, Ludovic Le Bigot, Nicolas Vibert To cite this version: Loïc Caroux, Ludovic Le Bigot, Nicolas Vibert. Impairment of Shooting Performance by Background Complexity and Motion. Experimental Psychology, Hogrefe, 2015, 62 2), pp.98-109. <10.1027/1618-3169/a000277>. <hal-01097375> HAL Id: hal-01097375 https://hal.inria.fr/hal-01097375 Submitted on 19 Dec 2014 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
PRE$PRINT$ Caroux,L.,LeBigot,L.,&Vibert,N.inpress).Impairmentofshootingperformanceby backgroundcomplexityandmotion.experimental,psychology.doi:10.1027/1618j3169/a000277 This,article,may,not,exactly,replicate,the,final,version,published,in,Experimental,Psychology,, 2014,by,Hogrefe,Publishing.,It,is,not,the,version,of,record,and,is,therefore,not,suitable,for,citation., Title: Impairmentofshootingperformancebybackgroundcomplexityandmotion Authors: LoïcCAROUX,LudovicLEBIGOT,NicolasVIBERT Affiliation: CentredeRecherchessurlaCognitionetl ApprentissageCeRCA) UMR7295 UniversityofPoitiers/UniversityofTours/CNRS France LoïcCarouxiscurrentlyaffiliatedtoINRIABordeauxSudWOuest,Talence,France) Correspondingauthor: LoïcCaroux INRIABordeauxSudWOuest EquipePhoenix 200avenuedelaVieilleTour 33405TalenceCedex France Email:loic.caroux@inria.fr 1
Abstract Inmanyvisualdisplayssuchasvirtualenvironments,humantasksinvolveobjectssuperimposedon bothcomplexandmovingbackgrounds.however,moststudiesinvestigatedtheinfluenceof backgroundcomplexityorbackgroundmotioninisolation.twoexperimentsweredesignedto investigatethejointinfluencesofbackgroundcomplexityandlateralmotiononasimpleshooting tasktypicalofvideogames.participantshadtoperformthetaskonthemovingandstaticversionsof backgroundsofthreelevelsofcomplexity,whiletheireyemovementswererecorded.the backgroundsdisplayedeitheranabstractexperiment1)oranaturalisticexperiment2)virtual environment.theresultsshowedthatperformancewasimpairedbybackgroundmotioninboth experiments.theeffectsofmotionandcomplexitywereadditivefortheabstractbackgroundand multiplicativeforthenaturalisticbackground.eyemovementrecordingsshowedthatperformance impairmentsreflectedatleastinparttheimpactofthebackgroundvisualfeaturesongazecontrol. Keywords Eyemovements;LowWlevelvisualfeatures;Virtualenvironments;Visualperception 2
1. Introduction$ Invirtualenvironments,mosttasksinvolvetheuseofobjectsthataresuperimposedona background.ingeneral,thesebackgroundsarecomplexanddynamicasinnaturalscenes.theyare composedofvariousvisualinformatione.g.,buildinginsides,landscapes)andcanmoveindifferent wayse.g.,linearorcircularmotion)inconnectionwiththetaskinwhichpeopleareengagede.g., Riecke,SchulteWPelkum,Avraamides,VonDerHeyde,&Bülthoff,2006;Trutoiu,Mohler,SchulteW Pelkum,&Bülthoff,2009). Asdetailedbelow,manystudieshaveshownthatbackgroundcomplexitye.g.,Chen&Hegdé,2012; Jie&Clark,2008;Wolfe,Oliva,Horowitz,Butcher,&Bompas,2002)ormotione.g.,Caroux,LeBigot, &Vibert,2013;Harrison,Thompson,&Sanderson,2010;Honda,2001;Kaminiarz,Krekelberg,& Bremmer,2007;Tozzi,Morrone,&Burr,2007)couldimpairpeople sperformanceinvarioustasks andsituations.ingeneral,theimpairmentcanbeexplainedbythepeople sgazebehavior,which reflectsattentionalprocessese.g.,henderson,chanceaux,&smith,2009;ilg,1997).however,few studiesinvestigatedthejointeffectsofbackgroundmotionandcomplexity.theobjectiveofthe presentexperimentswastofillthisgapbyinvestigatingthejointinfluencesofbackground complexityandbackgroundmotiononperformanceandgazebehaviorinavirtualenvironment. 1.1. Influence$of$background$complexity$on$performance$and$gaze$ behavior$ ThecomplexityofavisualsceneisusuallycharacterizedbylowWlevelvisualfeatures.Toqualifythe complexityofavisualscene,theconceptof clutter canbeusede.g.,asher,tolhurst,troscianko,& Gilchrist,2013;Beck,Lohrenz,&Trafton,2010;Neider&Zelinsky,2011;Wolfeetal.,2002).The clutterrepresentsthedensityofvisualinformationinascene.whentheclutterofavisualsceneis high,thesceneincludesagreatdensityofvariouscolororluminancecontrasts.whentheclutteris 3
low,onlyfewcontrastsarevisibleinthescene.thecomplexityofavisualscenehasanimpacton people sperformanceandassociatedgazebehaviorhendersonetal.,2009)invarioustasks,suchas visualsearche.g.,wolfeetal.,2002)orvideogameshootingtasksjie&clark,2008). Wolfeetal.2002)studiedvisualsearchincomplexvisualenvironmentsandproposedamodel basedonthe guidedsearch modelwolfe,1994).searchingforaniteminacomplexvisualscene canbeseparatedintwostages:theprewattentivestageandtheselectivestage.inthefirststage, parallelprocessingofvisualinformationisusedtoguidethedeploymentofattention,andcandidate targetsaresegmentedfromthebackground.inthesecondstage,attentionisorientedtowardsthe prewselecteditems,whichareprocessedfurthertoidentifythetarget.wolfeetal.2002)showed thatthemorecomplexthescenewas,themoreimperfecttheprewattentivesegmentationwas.in addition,thedurationofprocessingofprewselecteditemsdependedonthequalityoftheseparation ofitemsfromthebackground.hence,themorecomplexthevisualenvironmentwas,thelowerthe observer sperformancewasandtheslowertheobserversweretodetectthetarget.similarly,jie andclark2008)studiedtheeffectofbackgroundcomplexityontheperceptionofsuperimposed itemsinashootingtask.participantshadtodetecttargetsthatappearedrandomlyonastationary complexpicture,andtoshootthemasrapidlyaspossible.theauthorsshowedthatperformance timetoshoottargets)waslowerwhenthelocalclutteraroundthetargetwashigher. Thetimetoprocessadisplaycanalsobeassessedbyanalyzingobservers eyemovementsfora review,seerayner,2009).forexample,thedurationofsearchers eyefixationsisoftenusedto quantifytheamountofattentionalresourcesrequiredtoprocessvisualitemsintheenvironment. Hendersonetal.2009)showedthatinarealworldscene,themorecomplexthescenewas,the higherthemeandurationofeyefixationswas.thiswascoherentwithwolfeetal. s2002)findings aboutthetimeneededtodetectthetargetduringavisualsearchtaskperformedonacomplex background.thisreflectedthedifficultyfortheobservertoextractusefulinformationfromthelocal 4
visual noise.hence,themeandurationofeyefixationsisanindicatorofthesearchefficiency withinacomplexscene. 1.2. Influence$of$background$motion$on$gaze$behavior$and$ performance$ Oneofthebestknowneffectsofmovingbackgroundsinnaturalscenesorvirtualenvironmentsis theoptokineticnystagmusokn)triggeredbylargewscalemotionsofthevisualsurroundingse.g., Kim&Palmisano,2010;Rieckeetal.,2006).TheOKNisareflexive,conjugatemovementofboth eyesinwhichtwophasesalternate:theslowphasemovestheeyesinthedirectionofbackground motion,ideallyatthesamevelocity,whereasthefastphaseregularlybringsbacktheeyesinthe oppositedirectionilg,1997;waespe&schwarz,1987).theslowphaseoftheoknisa compensatoryeyemovementthatallowstheobservertoautomaticallykeepvisualinputstableon theretina.eventhoughtheslowandfastphasestendtocompensateeachother,theaveragegaze orientationisgenerallydivertedtowardswherethemovingscenecomesfrom,atleastwhenthe observerispassivelylookingatthesceneilg,1997).notethatanysingle,stationaryfixationpoint presentedontopofthemovingbackgroundcanbeusedbyobserverstovoluntarilycanceltheokn Ilg,1997). TheOKNhasbehavioralimplicationsforactivitiesperformedonmovingvisualbackgrounds.For example,theoknhasnegativeeffectsonobservers performanceinperceptivetasks.kaminiarzet al.2007)andtozzietal.2007)studiedtheimpactofoknonparticipants performanceinatarget localizationtask.participantshadtolocalizeabrieflyflashedtargetdisplayedonalaterallymoving, patternedbackground.theauthorsshowedthatvariouserrorsoflocalizationwereobservedduring OKNphases.Carouxetal.2013)studiedtheeffectofbackgroundmotionontheperceptionof superimposeditemsduringashootingtask.participantshadtodetecttargetsthatappeared randomlyonpatternedbackgrounds,andtoshootthemasrapidlyaspossible.theyshowedthat 5
performancetimetoshoottargets)waslowerwhenthebackgroundwaslaterallymovingthan whenitwasstationary.similarly,harrisonetal.2010)demonstratedthatbackgroundmotion decreasedperformanceinasimpletaskinvolvingtheintegrationofbriefauditoryandvisualsignals. ThevisualimagewasdisplayedonaheadWmounteddisplayandthebackgroundwastherealworld. Whentheparticipantswalkedorwhenthewallssurroundingtheparticipantsmoved,the performancewaslowerthanwhentheparticipantssatorwhenthewallswerestationary.insum, movingartificialorrealworldbackgroundsdooftendecreaseperformanceinsimpletaskssuchas targetlocalizationortargetshootingtasks. 1.3. The$present$study$ Thepresentstudyaimedatinvestigatingthejointinfluencesofbackgroundlateralmotionandvisual complexityonasimpleshootingtasksuchaswhatcanbefoundinvideogames.thegoalofthe shootingtaskusedintheexperimentswastoaimandshootasfastaspossibleatdifferentvisual targetsindicatedbyauditorycluestoobtainthebestscorepossible.thefirsthypothesiswasthatthe performanceislowerwhenthebackgroundisvisuallycomplexthanwhenitislesscomplexjie& Clark,2008;Wolfeetal.,2002).Becausepreviousstudiesshowedthatbackgroundmotionalso impairedperformanceintargetdetectiontaskscarouxetal.,2013;harrisonetal.,2010;kaminiarz etal.,2007;tozzietal.,2007),theperformanceimpairmentinducedbyvisualcomplexityshould interactwiththeimpairmentcausedbybackgroundmotion.thus,thesecondhypothesiswasthat theperformanceismoreimpairedbybackgroundcomplexitywhenthebackgroundismovingthan whenitisstatic.thesehypothesesweretestedintwosimilarexperiments.theonlydifference betweentheexperimentswasthenatureofthevisualelementsusedtodesignthebackground.the findingswereexpectedtobethesamewhateverthebackgroundvisualdisplay. 6
2. Experiment$1$ 2.1. Method$ 2.1.1. Participants$ TwentyWtwovolunteers16women,6men)tookpartintheexperiment.Theiraverageagewas19.9 yearssd=1.8)andtheiraveragelengthofschooling13.6yearssd=1.4).allparticipantswere nativefrenchspeakersandhadnormalorcorrectedwtownormalvision. 2.1.2. Apparatus$ AnonWinvasive,headWfree TobiiT120 eyewtrackerthatlookedlikea17 TFTcomputerscreen1280 x1024pixelsresolution)wasusedtomimicasmuchaspossiblenaturalinteractionwithavirtual environment.theeyetrackerwascontrolledviaacomputer,whichcollectedthedataandranthe taskprogram.gazepositionswereobtainedata120hzfrequencywithanaverageprecisionof0.5 degreeofvisualangleabout5mmonthescreen).becausethelaterallymovingbackgroundsusedin theexperimentsmovedleftwardsatabout12deg/sseebelow),thedatamayincludeoknslow phasesduringwhichtheacquisitionofinformationisstillongoingeventhoughtheobserver sgazeis movingrightwardsatthesamevelocity.hence,eyefixationsandsaccadesweredetectedusing velocitywbaseddetectionalgorithmsfromthe GazeAlyze softwareberger,winkels,lischke,& Höppner,2012).Fixationsweredefinedasanyperiodwheregazevelocitywaslessthan14deg/sfor atleast60ms.saccadesweredefinedasanyperiodwheregazevelocitywentover30deg/sformore than35ms.aspeakerthatwaslocatedinfrontofparticipantswithoutbiasofspatiallocation)was usedtodisplaysounds. 7
2.1.3. Material$ Thematerialwascreatedwith AdobeDirector11 software.threedifferentbackgroundsofvarious visualcomplexitiesweredesignedfigure1).theywereextractedfromthevideogame Childof Eden Ubisoft,2011)andwerecomposedofamainlygreenneutralpatternmainHSVcolorscale: Hue=120,Saturation=100,Value=10to70)scatteredwithabstractobjectsHSV:120,50W100,40W 100).Thecomplexitywasdeterminedaccordingtotheproportionofthebackgroundcoveredbythe objects,whichrepresentedtheclutter.thefirstversiononlyshowedtheneutralpatternnoclutter), thesecondoneshowedtheneutralpatternwithobjectscovering25%ofitssurfacelowclutter),and inthethirdonetheobjectscovered50%ofthebackgroundsurfacehighclutter).asstatedabove, whenthebackgroundwaslaterallymoving,itmovedleftwardsataspeedof121mm/sabout12 deg/s).thetargetandthedistractoroftheshootingtaskweredrawingsofacreature.fourcreature versionswereused.thecreaturecouldbebluehsv:228,74,25w84)orredhsv:7,74,25w84),and small85x66pixels,22x17mm,2,2x1,7degrees)orlarge85x99pixels,22x26mm,2.2x2.6degrees). Thecursorwasarepresentationofacrosshairof114pixelsdiameter30mm,3degrees).Six auditoryclueswererecordedwithamalenaturalvoice.theseclueswere left, right, blue, red, large and small gauche, droite, bleu, rouge, grand and petit infrench).their durationwas0.5second. [Figure1nearhere] 2.1.4. Design$and$procedure$ Thebackgroundcomplexityno,loworhighclutter)andmotionpresenceorabsence)were manipulatedwithinwparticipants. 8
Ashootingtaskwasused.Atthebeginningofeachtrial,thebackgroundwasdisplayedandanempty blacksquareof74mmsideabout7.4deg)wastransientlysuperimposedatthecentreofthescreen for1secondtoorienttheparticipant sgazetowardsthecentreofthedisplaywithoutcancellingthe effectsofbackgroundmotionsuchastheokn.participantswereinstructedtokeeptheirgazeas muchaspossiblewithinthesquare.theauditorycluewasdisplayedatthesametimethanthe square.thecluecouldbealocationclue left or right ),acolorclue blue or red )orasizeclue large or small ).Thetarget,thedistractorandthecursorappearedonthescreenallonthesame, randomhorizontalline.thecursorwasalwaysonthecentralverticalaxisofthescreen,whereasthe targetwasdisplayedrandomlyontherightorleftsideofthescreen.thehorizontalcoordinateof appearanceofthetargetbetweenthecursorandthescreenside)wasalsorandomlydetermined. Thedistractorwaslocatedattheexactoppositeofthetargetontheothersideofthescreencentral verticalaxis.thesizeandcolorofthedistractordifferedfromthetargetonlyonthevisualfeature thatcorrespondedtothenatureoftheclue.forexample,ifthecluewas red,thetargetwas necessarilyredbutcouldbelargeorsmall.thedistractorwasoftheoppositecolorhereblue)but hadthesamesizeasthetarget.participantshadtoaimatthetargetwiththehelpofthekeyboard buttons leftarrow and rightarrow,andtoshootatitbypushingthe space bar.participants wereabletomovethecursorandshootasoftenastheywishedwhilethetargetwasmissed,in otherwordswhilethecursorandthetargetwerenotsuperimposedatthetimeofshooting.when thetargetwashit,anothertrialbegan. Theexperimenterpresentedthisproceduretotheparticipantsasavideogame.Theywereaskedto touchasfastaspossibleeachtargetbyneglectingthedistractor.eachsetoftrialswaspresentedto theparticipantasonegame.sixgamesofsixtytrialswerepresentedtoeachparticipant,witha pausebetweeneachgame.theglobalscorewasgivenattheendofallblocks.alltrialsofeachgame wereperformedonthesamebackground,whichdidnotdisappearbetweeneachtrial.whenthe backgroundwasmoving,themotionwascontinuousanddidnotstopforthewholegame.theorder ofpresentationofthe6games2x3differentconditionsofmotionpresence/absenceand 9
complexity)perparticipantwaspseudowrandomized.ineachgame,theorderofpresentationofthe differentclueswasalsopseudowrandomized. 2.1.5. Dependent$measures$ Performancewasassessedusingthemeanresponsetimetohiteachtargetortocompleteeach trial)asthedependentmeasure.toexplaintheperformance,participants eyemovementswere analyzedusingsixdependentmeasures:themeannumberoffixationspertrial,themeandurationof fixations,theaveragelocationoffixationsonthedisplaydefinedbythehorizontal X andvertical Y coordinates),themeannumberofsaccadespertrialandtheaverageamplitudeofsaccades. Foreachtrial,onlytheeyefixationsandsaccadesthatweremadewhilesearchingforthetarget.In otherwords,boththefixationthatwasinterruptedbytheappearanceofthetargetanddistractor andthefixationthatwasongoingwhenthetargetwashitwerenotincludedintheanalysis.all variableswereanalyzedusingrepeatedmeasuresanovaswiththebackgroundmotionandthe backgroundcomplexityaswithinwparticipantsfactors.whenthemauchleysphericitytestwas significant,greenhousewgeissercorrectionwasapplied. 2.2. Results$ Alllateresponsesresponsetimesgreaterthan3000ms)wereexcludedfromanalyses.Thenumber oftrialsthatwereexcludedrepresentedonaverage2.1%ofthetotalnumberoftrialsperparticipant min=0.0%,max=13.3%).responsetimedatawerelogarithmicallytransformedbeforeanovas wereperformed.forclarityofpresentation,themeansoftheuntransformeddataarereportedin thetext,graphicandtable.themeansandstandarddeviationsofalldependentmeasuresare displayedintable1.theresultsoftheanovasandplannedcomparisonsthatwereperformedto analyzethedataaredisplayedintable2. 10
[Table1nearhere] [Table2nearhere] 2.2.1. Mean$response$time$ AsshownonFigure2,backgroundcomplexityhadaninfluenceontheresponsetime.Planned comparisonsdemonstratedthattheresponsetimewaslongerinthelowclutterconditionm=1392 ms,sd=264)thaninthenoclutterm=1341ms,sd=253),orhighclutterconditionsm=1359ms, SD=265).Thedifferencebetweenthesetwolastconditionswasnotsignificant.Backgroundmotion hadalsoanimpactontheresponsetime.theresponsetimewaslongeronthemovingbackground M=1404ms,SD=244)thanonthestaticoneM=1324ms,SD=272).However,theinteraction betweenthemotionandcomplexityfactorswasnotsignificant. [Figure2nearhere] 2.2.2. Eye$movement$data$ Qualitativeobservationoftheeyemovementdatadisplayedbyasampleofparticipantsshowedthat whenthebackgroundwasmoving,anoknconsistingofslowphasesorientedleftwardsinterrupted byquickphasesorientedrightwardswaspresentinbetweentrials.themaximumvelocityofslow phasesreached5to10deg/sdependingonparticipants.whenthetargetanddistractorappeared, theokndisappeared,andonlyfixationsandsaccadeswerevisible,probablybecausethetarget and/ordistractorwereusedasstationary anchoringpoints tocancelthenystagmusilg,1997). 11
Asexplainedinthemethodsection,onlytheeyefixationsandsaccadesthatweremadewhile searchingforthetargetwereanalyzed.hence,thefixationsandsaccadesthatwereanalyzed accountedforabout50%ofresponsetimes. Fixations, Inaccordancewiththeresponsetimedata,backgroundcomplexityhadaninfluenceonthenumber offixationsthatweremadewhilesearchingforthetarget.plannedcomparisonsdemonstratedthat thenumberoffixationswashigherinthelowclutterconditionthaninthenoclutterone.other comparisonswerenotsignificant,eventhoughparticipantstendedtomakemorefixationsinthelow clutterconditionthaninthehighclutterone.backgroundmotionhadalsoanimpactonthenumber offixations,whichwashigheronthemovingbackgroundthanonthestaticone.however,the interactionbetweenthetwofactorswasnotsignificant. BackgroundmotionhadanimpactonthehorizontalcoordinateX)offixations.Inaverage,fixations werelocatedmorerightwardsonthemovingbackgroundthanonthestaticone.background complexityhadnoimpactonthehorizontalcoordinateoffixations,buttheinteractionbetweenthe twofactorswassignificant.plannedcomparisonsdemonstratedthatwhenthebackgroundwas moving,thefixationswerelocatedmorerightwardsinthehighclutterconditionthaninthelow clutterone,andalsomorerightwardsinthelowclutterconditionthaninthenoclutterone.when thebackgroundwasstatic,incontrast,therewasnotanysignificanteffectofbackgroundcomplexity onthehorizontalcoordinateoffixations. Therewasnotanysignificanteffectofbackgroundcomplexityormotiononthemeandurationor theverticalcoordinatey)ofthefixations,oranysignificantinteractionbetweenthetwofactors. Saccades, Thenumberofsaccadesmadebytheparticipantswhilesearchingforthetargetwashigher,and theiraverageamplitudelower,onthemovingbackgroundthanonthestaticone.therewasnotany 12
significanteffectofbackgroundcomplexityonthemeannumberortheaverageamplitudeof saccades,oranysignificantinteractionbetweenthetwofactors. 3. Experiment$2$ 3.1. Method$ Theapparatus,design,procedureandparticipantsofExperiment2werethesameasthoseof Experiment1.ThematerialwasthesameasinExperiment1,butthethreebackgroundswere extractedfromthevideogame SimCity4 ElectronicArts,2003)Figure1),andwerecomposedof amainlygreenneutralpatternscatteredhsv:75,30w50,30)withnaturalisticobjectshsv:75,0w50, 20). 3.2. Results$ Asinexperiment1,alllateresponsesresponsetimesgreaterthan3000ms)wereexcludedfrom analyses.thenumberoftrialsthatwereexcludedrepresentedonaverage2.0%ofthetotalnumber oftrialsperparticipantmin=0.0%,max=10.8%).responsetimedatawerelogarithmically transformedbeforeanovaswereperformed.forclarityofpresentation,themeansofthe untransformeddataarereportedinthetext,graphicandtable.themeansandstandarddeviations ofalldependentmeasuresaredisplayedintable3.theresultsoftheanovasandplanned comparisonsthatwereperformedtoanalyzethedataaredisplayedintable4. [Table3nearhere] [Table4nearhere] 13
3.2.1. Mean$response$time$ AsshownonFigure3,backgroundcomplexityhadnotanysignificantinfluenceontheresponsetime. Incontrast,backgroundmotionhadanimpactontheresponsetime,whichwaslongeronthe movingbackgroundm=1360ms,sd=262)thanonthestaticonem=1291ms,sd=250). Furthermore,theinteractionbetweenbackgroundmotionandcomplexitywassignificant.Planned comparisonsshowedthatwhenthebackgroundwasmoving,theresponsetimewaslongerinthe lowclutterconditionthaninthenoclutterone.othercomparisonswerenotsignificant.whenthe backgroundwasstatic,theresponsetimewasnotsignificantlydifferentbetweenthethreeclutter conditions. [Figure3nearhere] 3.2.2. Eye$movement$data$ AsinExperiment1,qualitativeobservationoftheeyemovementdatadisplayedbyasampleof participantssuggestedthatwhenthebackgroundwasmoving,anoknwastriggeredinbetween trials.again,onlytheeyefixationsandsaccadesthatweremadewhilesearchingforthetargetwere analyzed.theyaccountedforabout40%ofresponsetimes. Fixations, Eventhoughparticipantstendedtomakemorefixationswhenthebackgroundwasmoving,there wasnotanysignificanteffectofbackgroundcomplexityormotiononthemeannumberoffixations thatweremadewhilesearchingforthetarget,oranysignificantinteractionbetweenthetwo factors. 14
Similarly,therewasnotanysignificanteffectofbackgroundcomplexityormotiononthemean durationortheverticalcoordinatey)ofthefixations,oranysignificantinteractionbetweenthetwo factors AsinExperiment1,backgroundmotionhadanimpactonthehorizontalcoordinateX)offixations. Thefixationswerelocatedmorerightwardsonthemovingbackgroundthanonthestaticone.In contrast,therewasnotanysignificanteffectofbackgroundcomplexityonthehorizontalcoordinate offixations,oranysignificantinteractionbetweenthetwofactors. Saccades, AsinExperiment1,theaverageamplitudeofsaccadeswasloweronthemovingbackgroundthanon thestaticone.but,incontrast,therewasnotanysignificanteffectofbackgroundmotiononthe meannumberofsaccades.therewasnotanysignificanteffectofbackgroundcomplexityonthe meannumberortheamplitudeofsaccades,oranysignificantinteractionbetweenthetwofactors. 4. Discussion$ Thefirsthypothesiswasthattheperformanceislowerwhenthebackgroundiscomplexthanwhenit islesscomplex.itwaspartiallysupported.theresponsetimevariedsignificantlyaccordingtothe backgroundcomplexityonlyinexperiment1.furthermore,theresponsetimewashigherinthelow clutterconditionthaninboththenoclutterandhighclutterconditions.inaccordancewiththese data,participantsmademoreortendedtomakemorefixationswhilesearchingforthetargetinthe lowclutterconditionthaninthenoclutterorhighclutterconditions.accordingtobecketal.2010) andwolfeetal.2002),theperformanceimpairmentinavisualsearchtaskwouldlinearlyincrease withthevisualcomplexityofthescene.thus,theparticipants responsetimeshouldhavebeen higherinthehighclutterthaninthelowcluttercondition.hencethewaythevisualcomplexityof backgroundswassetinthepresentstudymaynothavebeencompletelyadequate.accordingtothe results,thepresenceofobjectssuperimposedonapatterndoesincreasethevisualcomplexityofthe 15
background,butincreasingtheproportionofthesurfacetheycoverdoesnotseemtoincrease backgroundcomplexity,andmayactuallydecreaseit.thequantityofsalientvisualcontrastsinthe backgroundmaynotdirectlydependontheproportionofthescenecoveredbytheobjects. Inordertohaveanothermeasurethanthelevelofcluttertoqualifythecomplexityofeach backgroundusedinthepresentstudy,saliencymapswerecomputedfromthevariousbackgrounds usedinthetwoexperimentsusingthe Saliencytoolbox2.3 Walther&Koch,2006),which implementsthesaliencymodeloriginallyproposedbyittiandkoch2000)figure4).thismodelis abletopredicthumangazeallocationonthedifferentpartsofvisualscenesbycomputingregionsof saliency.intheresultantsaliencymaps,lowvaluesindicatetheregionsofthescenethatarenot salient,whereashighvaluesindicatetheregionsthataresalientandtendtoattracttheobserver s attention. QualitativeobservationofthesaliencymapsobtainedforthebackgroundsusedinExperiment1 showthattherewereseveralhighlysalientregionsinthelowclutterbackground,whereasthe overallsaliencyofsalientregionswaslowerinthenoclutterandhighclutterbackgrounds. Consequently,theparticipants gazewasprobablymoreimpactedbylowwlevelvisualfeaturesinthe lowclutterbackgroundthanintheotherones.thisisinaccordancewithresponsetimedata,which demonstratedthatperformancewasmoreimpairedbythelowclutterbackgroundthanbythehigh clutterone. ThesaliencymapsobtainedforthebackgroundsusedinExperiment2werequitesimilartothose obtainedinexperiment1,i.e.displayedmorehighlysalientregionsinthelowclutterconditionthan inthetwootherones.however,thedifferencebetweenthethreetypesofbackgroundwasless importantthaninexperiment1.thiscouldexplainwhytheparticipants gazeandperformancewere notsignificantlyimpactedbymanipulationsofbackgroundcomplexity,butonlybythejoint manipulationofbothbackgroundmotionandcomplexity. 16
[Figure4nearhere] Insum,inthesetwoexperiments,themostvisuallycomplexbackgroundwasapparentlythatwhere thesuperimposedobjectscovered25%,andnot50%,ofthescreensurface.whentheproportionof thescreencoveredbyobjectswastoohigh,theimpactofthebackgroundwasnotsignificantly differentfromthatofthebasicbackgroundwherenoobjectwaspresent.hence,thesaliencyscale ofavisualsceneseemstogiveabettermeasureofcomplexitythanthelevelofclutter,but complementaryexperimentsareneededtodeterminetowhatextentthisistrue. ContrarytowhatwasexpectedaccordingtoHendersonetal.2009),theanalysisofeyemovements didnotdemonstrateanysignificantinfluenceofbackgroundcomplexityonthedurationofeye fixations.thisconfirmsthattheproportionofthescenecoveredbyobjectsmaynotbeanideal measureofbackgroundcomplexity.alternatively,theinfluenceofthisfactoronthedurationof fixationsmaybetooweakinthepresentconditionstobeobservable. Thesecondhypothesiswasthatwithacomplexbackground,theperformanceisevenmoreimpaired when,inaddition,thebackgroundismoving.itwaspartiallysupported.theresultsshowedthatthe performancewasalwayslowerwhenthebackgroundwasmovingthanwhenitwasstatic,whatever thetypeofbackground.theseresultsareinlinewiththoseofpreviousstudiescarouxetal.,2013; Harrisonetal.,2010;Kaminiarzetal.,2007;Tozzietal.,2007).Theanalysisofeyemovements showedthatthisimpairmentmaybeduetotheneedtocanceltheokntriggeredbybackground motion,whichwoulddisturbgazecontrolandinformationprocessingwhiletheparticipantsare searchingforandshootingatthetarget.indeed,whenthebackgroundwasmoving,theaveragegaze orientationwasdeviatedtowardsthesideoforiginofthemotionasexpectedinthepresenceofokn Ilg,1997).Inaddition,participantsmadesmallersaccadesinbothexperimentsandtendedtomake moresaccadesandfixationsonthedisplay,thoughsignificancewasreachedonlyinexperiment1. 17
Contrarytopredictions,however,thepredictedinteractionbetweenthebackgroundmotionand complexitywassignificantonlyinexperiment2.theresultsshowedthatwhentherewasnoclutter orahighclutter,therewasnotanysignificantdifferenceofresponsetimebetweenthestaticand movingbackgrounds.whentheclutterwaslow,theresponsetimewashigheronthemoving backgroundthanonthestaticone.inthisexperiment,thepresenceofobjectssuperimposedonthe neutralpatternimpairedperformanceonlywhenthebackgroundwasmoving,andonlywhenthe proportionofthebackgroundsurfacecoveredbyobjectswasnottoohighi.e.whenthebackground includednumeroushighlysalientregions). 4.1. Conclusions$and$outlook$ Thepresentstudyshowedthattheperformanceinasimpleshootingtaskisoftenimpairedby backgroundmotion,inaccordancewithpreviousstudieswithothertaskscarouxetal.,2013; Harrisonetal.,2010;Kaminiarzetal.,2007;Tozzietal.,2007).Moreover,thepresentstudy demonstratedthattheeffectsofbackgroundvisualcomplexityandmotionontheperformanceare additiveforoneofthebackgroundsexperiment1)andmultiplicativefortheotheroneexperiment 2). However,onelimitofthepresentstudyisthatthetwoexperimentsdidnotgiveexactlythesame results.theimpactofbackgroundcomplexityonparticipants performancewasdifferentaccording tothebackgroundthatwasused.inexperiment1,thesimpleeffectofbackgroundcomplexitywas significant.inexperiment2,thesimpleeffectofbackgroundcomplexitywasnotsignificant,butthere wasasignificantinteractionwithbackgroundmotionsuchthatbackgroundcomplexityhada significantimpactonperformancewhenthebackgroundwasmoving. Thisdifferenceofresultscanonlybeduetothenatureofthevisualelementsthatwereusedinthe twobackgrounds.allotherparametersoftheexperimentswerestrictlysimilar.amongpossible explanations,thedifferentarrangementsoftheobjectsontheneutralpattern,orthedifferent 18
shadesofgreensusedforthepatterns,theobjectsorbothseemtocreatedifferentialcontrastsand localcomplexitiesbetweenthetwobackgrounds.inaddition,thecolorsofthedifferentvisual elementsusedinthetwobackgroundsweredifferentintermsofcolorhue,saturationand value.allthismayinfluencethedifficultyofthetargetanddistractorperceptiontask.forexample, previousstudiesshowedthatvisualsearchperformancemayvarydependingonothertypesofloww levelfeaturesofthebackground,suchasluminance,orientationandspatialfrequencye.g.,devries, Hooge,Wertheim,&Verstraten,2013).Furtherexperimentsarenecessarytoexplaintowhatextent thesespecificlowwlevelfeaturescaninfluencetheperceptionanduseofobjectssuperimposedona structuredbackground,incombinationwithbackgroundcomplexityandmotion. 5. Acknowledgments$ TheauthorsthankJeanPylousterforhistechnicalassistanceintheanalysisoftheeyemovement data,especiallyintheadaptationofthe GazeAlyze softwarepackageforthetobiit120data.loïc CarouxwassupportedbyaPh.D.fellowshipfromtheDirectionGénéraledel ArmementDGA, FrenchMinistryofDefense)andfollowedintheframeofthisfellowshipbyDidierBazalgette. 6. References$ Asher,M.F.,Tolhurst,D.J.,Troscianko,T.,&Gilchrist,I.D.2013).Regionaleffectsofclutteron humantargetdetectionperformance.journalofvision,135),article25,1 15. doi:10.1167/13.5.25 Beck,M.R.,Lohrenz,M.C.,&Trafton,J.G.2010).Measuringsearchefficiencyincomplexvisual searchtasks:globalandlocalclutter.journalofexperimentalpsychology:applied,16,238 250.doi:10.1037/a0019633 Berger,C.,Winkels,M.,Lischke,A.,&Höppner,J.2012).GazeAlyze:aMATLABtoolboxforthe 19
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Table1.MeansM)andstandarddeviationsSD)ofdependentmeasuresaccordingtobackground complexityandmotioninexperiment1. Noclutter Lowclutter Highclutter M SD M SD M SD Meanresponsetimeinms) Staticbackground 1298 262 1375 292 1299 257 Movingbackground 1384 237 1409 234 1419 262 Meannumberoffixations Staticbackground 1.61 0.63 1.96 1.09 1.64 0.71 Movingbackground 1.98 0.86 2.11 0.91 2.06 0.98 Meandurationoffixationsinms) Staticbackground 258 114 235 84 274 103 Movingbackground 253 97 234 79 250 77 Averagepositionoffixationsinpixels) Horizontal*coordinate*X)* Staticbackground 632 49 631 53 626 46 Movingbackground 642 41 658 43 674 57 Vertical*coordinate*Y)* Staticbackground 494 47 476 51 477 50 Movingbackground 489 51 490 46 495 37 Meannumberofsaccades Staticbackground 2.13 0.48 2.36 0.54 2.18 0.60 Movingbackground 2.49 0.60 2.60 0.62 2.55 0.83 Averageamplitudeofsaccadesindegrees) Staticbackground 5.35 0.83 5.02 0.77 5.06 0.56 Movingbackground 4.84 0.68 4.88 0.63 4.81 0.56 23
Table2.ResultsofANOVAsandplannedcomparisonsperformedinExperiment1. ANOVA Plannedcomparison df* F@ratio p@value η 2 p* Meanresponsetime BackgroundComplexity 2,42 4.87 <.05.19 Novs.Low 1,21 7.66 <.05 W Novs.High 1,21 1.02.32 W Lowvs.High 1,21 4.90 <.05 W BackgroundMotion 1,21 32.08 <.001.60 BackgroundComplexityxMotion 2,42 2.08.14 W Meannumberoffixations BackgroundComplexity 2,42 3.89 <.05.16 Novs.Low 1,21 7.24 <.05 W Novs.High 1,21 0.57.46 W Lowvs.High 1,21 3.02.10 W BackgroundMotion 1,21 7.57 <.05.27 BackgroundComplexityxMotion 2,42 1.41.26 W Meandurationoffixations BackgroundComplexity 2,42 2.22.12 W BackgroundMotion 1,21 0.71.41 W BackgroundComplexityxMotion 2,42 0.68.51 W Averagepositionoffixations Horizontal*coordinate*X)* BackgroundComplexity 2,42 3.38.06 W BackgroundMotion 1,21 48.34 <.001.70 BackgroundComplexityxMotion 2,42 6.37 <.01.23 Static,Novs.Low 1,21 0.04.84 W Static,Novs.High 1,21 0.50.49 W Static,Lowvs.High 1,21 0.74.40 W Moving,Novs.Low 1,21 6.69 <.05 W Moving,Novs.High 1,21 26.27 <.001 W Moving,Lowvs.High 1,21 5.07 <.05 W Vertical*coordinate*Y)* BackgroundComplexity 2,42 0.57.57 W BackgroundMotion 1,21 2.33.14 W BackgroundComplexityxMotion 2,42 2.38.11 W Meannumberofsaccades BackgroundComplexity 2,42 2.76.08 W BackgroundMotion 1,21 18.24 <.001.47 BackgroundComplexityxMotion 2,42 0.47.63 W Averageamplitudeofsaccades BackgroundComplexity 2,42 1.68.20 W BackgroundMotion 1,21 10.93 <.01.34 BackgroundComplexityxMotion 2,42 2.32.11 W Note.No=NoClutter;Low=LowClutter;High=HighClutter;Static=StaticBackground;Moving=Moving Background.Plannedcomparisonsaredisplayedonlywhenthecorrespondingmaineffectorinteractionwas significant.partialη²aredisplayedonlywhenthemaineffectsorinteractionsweresignificant. 24
Table3.MeansM)andstandarddeviationsSD)ofdependentmeasuresaccordingtobackground complexityandmotioninexperiment2. Noclutter Lowclutter Highclutter M SD M SD M SD Meanresponsetimeinms) Staticbackground 1277 248 1276 258 1320 246 Movingbackground 1314 229 1412 297 1354 250 Meannumberoffixations Staticbackground 1.38 0.53 1.40 0.59 1.47 0.66 Movingbackground 1.50 0.56 1.44 0.65 1.60 0.80 Meandurationoffixationsinms) Staticbackground 236 113 247 125 211 86 Movingbackground 231 69 204 48 204 73 Averagepositionoffixationsinpixels) Horizontal*coordinate*X)* Staticbackground 644 55 633 64 628 60 Movingbackground 652 56 663 54 648 58 Vertical*coordinate*Y)* Staticbackground 470 77 498 53 479 59 Movingbackground 480 52 480 63 491 51 Meannumberofsaccades Staticbackground 1.87 0.63 1.81 0.76 1.95 0.82 Movingbackground 2.00 0.64 1.89 0.80 1.98 0.95 Averageamplitudeofsaccadesindegrees) Staticbackground 5.70 1.08 5.61 1.04 6.04 1.57 Movingbackground 5.23 0.98 5.70 1.05 5.51 1.36 25
Table4.ResultsofANOVAsandplannedcomparisonsperformedinExperiment2. ANOVA Plannedcomparison df* F@ratio p@value η 2 p* Meanresponsetime BackgroundComplexity 2,42 2.65.08 W BackgroundMotion 1,21 6.71 <.05.70 BackgroundComplexityxMotion 2,42 3.81 <.05.66 Static,Novs.Low 1,21 0.01.97 W Static,Novs.High 1,21 3.56.07 W Static,Lowvs.High 1,21 2.87.10 W Moving,Novs.Low 1,21 6.97 <.05 W Moving,Novs.High 1,21 1.88.18 W Moving,Lowvs.High 1,21 3.07.09 W Meannumberoffixations BackgroundComplexity 2,42 1.01.37 W BackgroundMotion 1,21 1.92.18 W BackgroundComplexityxMotion 2,42 0.32.73 W Meandurationoffixations BackgroundComplexity 2,42 1.40.26 W BackgroundMotion 1,21 1.76.20 W BackgroundComplexityxMotion 2,42 1.14.33 W Averagepositionoffixations Horizontal*coordinate*X)* BackgroundComplexity 2,42 0.86.43 W BackgroundMotion 1,21 20.36 <.001.49 BackgroundComplexityxMotion 2,42 1.55.22 W Vertical*coordinate*Y)* BackgroundComplexity 2,42 2.00.15 W BackgroundMotion 1,21 0.03.87 W BackgroundComplexityxMotion 2,42 1.74.19 W Meannumberofsaccades BackgroundComplexity 2,42 0.90.41 W BackgroundMotion 1,21 0.96.34 W BackgroundComplexityxMotion 2,42 0.30.74 W Averageamplitudeofsaccades BackgroundComplexity 2,42 2.20.12 W BackgroundMotion 1,21 6.05 <.05.22 BackgroundComplexityxMotion 2,42 2.29.11 W Note.No=NoClutter;Low=LowClutter;High=HighClutter;Static=StaticBackground;Moving= MovingBackground.Plannedcomparisonsaredisplayedonlywhenthecorrespondingmaineffector interactionwassignificant.partialη²aredisplayedonlywhenthemaineffectsorinteractionswere significant. 26
Experiment1 Experiment2 No clutter Backgroundcomplexity Low clutter High clutter Figure1.BackgroundsusedinExperiment1andExperiment2,withdifferentexamplesoflocationsofatarget, adistractorandthecursor.foreachexperiment,threebackgroundsofvariouscomplexitiesweredesigned. Thecomplexitywasdeterminedbytheclutter,i.e.theproportionoftheinitial,neutralpatterncoveredbythe superimposedobjects. 27
MeanresponseFmems) 2200 2000 1800 1600 1400 1200 1000 Movingbackground Stazcbackground 800 700 0 Nocluyer Lowcluyer Highcluyer Backgroundcomplexity Figure2.Meanresponsetimeinms)tohiteachtargetineachconditionofbackgroundcomplexityandmotion inexperiment1,representedonalogarithmicallyspacedaxis.theerrorbarsrepresent±1standarderrorofthe mean. 28
MeanresponseFmems) 2200 2000 1800 1600 1400 1200 1000 Movingbackground Stazcbackground 800 700 0 Nocluyer Lowcluyer Highcluyer Backgroundcomplexity Figure3.Meanresponsetimeinms)tohiteachtargetwithineachconditionofbackgroundcomplexityand motioninexperiment2,representedonalogarithmicallyspacedaxis.theerrorbarsrepresent±1standard errorofthemean. 29
!! Experiment!1! Abstractbackground Experiment!2! Correspondingsaliencymap Correspondingsaliencymap Naturalisticbackground No clutter Background!Complexity! Low clutter High clutter Figure'4.BackgroundsusedinExperiments1and2withthecorrespondingsaliencymaps.Thebrighterregionswithinthesaliencymapsindicatehigher valuesofsaliency. 30