DOI: 10.4018/ijmhci.2017070101

International Journal of Mobile Human Computer InteractionVolume 9 • Issue 3 • July-September 2017

Copyright©2017,IGIGlobal.CopyingordistributinginprintorelectronicformswithoutwrittenpermissionofIGIGlobalisprohibited.

Using Multimodal Displays to Signify Critical Handovers of Control to Distracted Autonomous Car DriversIoannis Politis, School of Computing Science, University of Glasgow, Glasgow, UK

Stephen Brewster, School of Computing Science, University of Glasgow, Glasgow, UK

Frank Pollick, School of Psychology, University of Glasgow, Glasgow, UK

ABSTRACT

Untilfullautonomyisachievedincars,driverswillstillbeexpectedtotakeovercontrolofdriving,andcriticalwarningswillbeessential.Thispaperpresentsacomparisonofabstractversuslanguage-basedmultimodalwarningssignifyinghandoversofcontrol inautonomouscars.Whileusinganautonomouscarsimulator,participantsweredistractedfromtheroadbyplayingagameonatablet.Anautomationfailuretogetherwithacarinfrontbrakingwasthensimulated;ararebutverycriticalsituationforanon-attentivedrivertobein.Multimodalabstractorlanguage-basedwarningssignifyingthissituationwerethendelivered,eitherfromthesimulatororfromthetablet,inordertodiscoverthemosteffectivelocation.Resultsshowedthatabstractcues,includingaudio,andcuesdeliveredfromthetabletimprovedhandovers.Thisindicatesthepotentialofmovingsimplebutsalientautonomouscarwarningstowhereagamingsidetasktakesplace.

KeywoRDSAudio, Autonomous Cars, Games, Handover, Multimodal Feedback, Speech, Tactile, Tactons, Urgency, Visual, Warnings

INTRoDUCTIoN

Autonomouscarsarebecomingamoreandmorepopulartopicofresearch,althoughnotwithoutconcernsfromthepublicoverthesafetyofthisnewtechnology(Kyriakidis,Happee,&Winter,2014).Toaddresssuchworries,thereiscarefulexaminationofroadaccidentsinvolvingautonomousvehiclesfromtechnologyproviders(Google,2015b).Thisshowstheimportanceofsafetywhileautomationisbecomingmorerobust.Carautonomyisastagedratherthanbinaryprocess,withlevelsofautonomyincreasingasdriverinvolvementdecreases(NationalHighwayTrafficSafetyAdministration,2013;SAEJ3016&J3016,2014).Therefore,userinterfacesarerequiredthatimprovesafetywhendriverinvolvementisreducedbutstillnecessary.Thehandover,thepointoftransitionofcontrolfromthecartothedriver,andviceversa,isacriticalpartofthisinteraction.Aneffectivewarningmechanismforsuchacriticalcaseisessential,aslackofclarityoverwhohascontrolofthevehicleatagivenmomentcanbecatastrophic,e.g.(Politis,Brewster,&Pollick,2015a).

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Inparallel,asvehicleautomation increases,driversaremore likely toengage in tasksotherthandriving.Gamingisapopularactivitythatdriversareexpectedtoengageinwhilethecarisinautonomousmode,andisatopicofongoingresearch,e.g.(Krome,Goddard,Greuter,Walz,&Gerlicher,2015;Neubauer,Matthews,&Saxby,2014).Duetothehighlevelofconcentrationrequiredbyagame,aparticularlydemandingscenariowouldbeattendingtoacriticalhandoverwhilegaming.Acriticalhandoveroftenexaminedisanautomationfailure,sinceithappensunexpectedly,leavinglittletimetoreact(Gold,Damböck,Lorenz,&Bengler,2013;Moketal.,2015;Pfromm,Khan,Oppelt,Abendroth,&Bruder,2015).Signifyinghandoverswithmultimodalwarnings(Naujoks,Mai,&Neukum,2014;Politisetal.,2015a),usingvaryingmessagecontents (Kooetal.,2014)andevaluatingtransitiontimes(Goldetal.,2013;ChristianGold&Bengler,2014)areimportantaspectsofthiscriticalcase.However,thereisnoworkonhowcriticalhandoverscanbefacilitatedbymultimodalwarningsoriginatingfromthegamearea.Inthisstudy,weuseanengagingtabletgamingtaskandtestthetimerequiredtoresumedrivingduringanautomationfailure.Handovernotificationsaremovedtothetabletandabstractversuslanguage-basedmultimodalwarningsarecomparedasalertsforthisscenario,bothbeingnovelinterventions.

Multimodal Displays Varying in UrgencyMultimodaldisplayshaveconsistentlyshownadvantagesinalertingdriverstovariousroadevents.Simplespatialvibrotactilecuescomingfromthedirectionofathreatimprovedreactiontimesofdrivers(Ho,Tan,&Spence,2005).Ho,Reed&Spence(Ho,Reed,&Spence,2007)showedaddedbenefitwhenavibrotactilecueandacarhornsoundweredeliveredincombination.Thebenefitofdirectionalityinthecueswasalsoobservedby(Serrano,DiStasi,Megías,&Catena,2011),whofoundimprovedrecognitionperformanceofwhetheraroadscenewashazardousornotwhencueswerepresentedformthedirectionofthehazard.Inourstudy,wepresentthecueseitherfromthefront,whereathreatisapproaching,orfromthetabletonwhichtheparticipantsareplayingagame.Inthisway,weevaluatetheeffectofwarningsfromtheareawhichtheparticipantsarefocusedoncomparedtothedirectionofanapproachingthreatwhichtheyarenotattentiveto.

In termsofdesign, reflecting theurgencyof theevent in thewarninghasrepeatedlyshownbenefits.Politis,Brewster,&Pollick(2014a,2013,2014b)usedallunimodal,bimodalandtrimodalcombinations of cues varying in urgency to achieve lower response times and higher perceivedurgencyformoreurgentcues.Inthispaper,weusetheseresultstodesignmultimodalwarningsthatconvey the increasedurgencyneededforacriticalsituation.Further,Politis,Brewster&Pollick(2015b)extendedthecomparisoninallunimodal,bimodalandtrimodalcombinationsofabstractandlanguage-basedwarningsandfoundanadvantageofabstractcuesintermsofrecognitiontimesinanon-criticalsituation,butnodifferenceintermsofreactiontimesinthepresenceofacriticalevent.Inthiswork,wecomparehighlyurgentabstractandlanguage-basedmultimodalwarningspresentedfromdifferentlocationsinthecontextofautonomouscars,acomparisonthathasneverbeenattempted.

Handovers of Control in Autonomous CarsThecaseofanautomationfailurehasbeenstudiedinthepastasalikelyreasonforahandoverofcontrol.Goldetal.(2013)investigatedautomationfailureswhendriversweredistractedthroughatabletsidetask.Apuretoneandavisualiconcalledthedriversbacktothewheelduringanunexpectedevent.Thesewarningswereeitherdelivered5secor7secbeforetherequiredhandover.Itwasfoundthat5secwasabettertimetopreparedriverstoresumecontrol.Gold&Bengler(2014)extendedthisdiscussion,reportingthatduringahandoverofcontrol,bothtime(howlongittakes)aswellasquality(drivingperformanceduringandafterresumptionofcontrol)areimportantissuestobeconsidered.Inourwork,weusetheaboveideas,bysimulatinganautomationfailurethatcoincideswithacriticalevent,whichmakesdriverinterventionessential.Wealsomeasurebothtimeandqualityof thecar todriverhandovers in thisscenarioandpresentsimilarorquicker timesof transitionsachievedwiththeusedwarnings.

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Intermsofhandoverwarningdesign,Naujoksetal.(2014)investigatedahandoverfromthecartothedriverduetoanautomationfailure.Apuretoneandaflashingicononthedashboardcreatedshorterhandovertimesandbetterdrivingbehaviourwhencombinedcomparedtotheiconalone.Telpaz,Rhindress,Zelman,&Tsimhoni(2015)usedahapticseatdisplayingthepositionofanapproachingvehiclefromthebackusingamappingwithtactilealerts.Theuseoftheseatalongwithasimpleaudioandvisualindicationimprovedhandovertimesandsatisfactioncomparedtotheabsenceoftheseat.WalchLange,Baumann,&Weber(2015)usedspeechandtexttoalertdriversabouthandoversduringasharpcurve,whenavehiclewasblockingtheroadorwhentherewasnohazard.Inallcasesexceptthesharpcurve,3secwasanadequatetimeforasafehandoverintermsofresponsetimesandcomfortableintermsofparticipantresponses.Politisetal.(2015a)madeadetailedevaluationofaudio,visualandtactilelanguage-basedwarningstosignifyhandoversbetweenthecarandadistracteddriverwhowasplayingagame.Theyfoundthatmoreurgenthandoverwarningswereidentifiedassuchinurgencyratingsandcreatedshorterhandovertimes.Visualwarningspresentedfromthedrivingsimulatorcausedslowerreactiontimes,sincevisualattentionwasdirectedtoatabletgameandparticipantsoftenmissedthesecues.Thisledtoadangeroussituationwherethedriverswerenotawarethattheyhadcontrol.WeaddresstheissuediscoveredinPolitisetal.(2015a)bymovingthewarningstothefocusofinteraction.Allwarningsarepresentedfromeitherthesimulatororatablet.Further,wecomparetheeffectivenessofcuesvaryinginmessagecontent,byusingabstractorlanguage-basedwarningssignifyingacriticalhandover.Thisisanovelapproachbothintermsofwarninglocationaswellasmessagecontent.

Driver Distraction in Autonomous CarsWhenacarispartiallyorfullyautonomous,theabsenceofadrivingtaskallowsthedrivertoengageinotheractivities.Neubaueretal.(2014)foundthattheengagementwithatriviagameoraphoneconversationduringadrivethatinvolvedautomatedandmanualpartsreducedfatigueandimproveddrivingmetricswhenparticipantshadcontrolofthevehicle.However,engagementwithasecondarytaskcreatedhigherreactiontimestoanunexpectedevent.Milleretal.(2015)alsofoundthatmediaconsumptiononamobiledevicereducedfatigueofdriversanddidnotslowhandoverswheninvitedbacktodrivingshortlybeforeenteringanareaofincreasedhazard.Theirhandoverwarningswerevisualandauditory,comingeitherfromthe tabletor thedashboard,butnocomparisonbetweenlocationswasmade.

Otherthanthestudiesdescribedabove,interactionwithgamesisalittleexploredtopic,withavailablestudiesmainlyincaseswherethecarisfullyautonomousandnointerventionisexpected(seeforexample(Kromeetal.,2015;Terkenetal.2013)).Further,resumingcontrolwiththehelpofwarningsoriginatingfromtheareaofthegaminginteractionasopposedtothecarhasnotbeenstudied.Weaddressthisgapinourexperimentbyinvestigatingasetofurgentmultimodalwarningsdesignedforanautomationfailure,requiringimmediatedriverattention.Wedeliverthewarningseitherfromthesimulator,whichisthemostcommonapproachintheliteratureorfromatabletwheretheuserisplayingagameasasecondarytask.Differentwarningdesignsareused,utilisingabstractandlanguage-basedcuesneverbeforecomparedinthissetting.

wARNING DeSIGN

Thewarningsdesignedaddressedahighlyurgentsituation,whereacarwouldhandovercontroltothedriverduringacriticalevent,duetoanautomationfailure.Theabstractwarningsconsistedofpuretones,coloursorvibrationsdeliveredasrepeatedpulses,asinPolitisetal.(2013).Inlinewiththisstudy,thewarningshadanincreasedpulseratetoconveyhighurgency.Theyconsistedof8pulseshaving0.1secsinglepulsedurationandinterpulseintervalandhad1.5secduration.Theauditorywarningvariedadditionallyinbasefrequency(1000Hz)inlinewithEdworthy,Loxley,&Dennis(1991).AsinPolitisetal.(2013),thevisualwarningalsovariedincolourandwasRed

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(RGB(255,0,0)).Thetactilewarninghadafrequencyof150Hz,thenominalcentrefrequencyoftheELV-1411ATactor1,usedtodelivervibrationalmessages.InlinewithPolitisetal.(2015b),theabstractaudioandtactilecueshadthesameintensityasthespeechcues.Simultaneousdeliveryofunimodalsignalswasusedinthemultimodalcues,creatingasynchronouseffectofsound,vibrationandvisuals.

Forthelanguage-basedwarnings,thespeechmessageusedwastakenfromPolitisetal.(2015a).ItwasahighprioritymessageaccordingtoLee,Bricker,&Hoffman(2008)andSAE(2002),withtheword“Danger!”added in thebeginning to increaseperceivedurgency, in linewithBaldwin(2011)Edworthy,Hellier,Walters,Clift-Mathews,&Crowther(2003)andPolitisetal.(2014b).Attheendofthemessageanexplanationthatthedriverhadvehiclecontrolwasadded,asinPolitisetal.(2015a).Theresultingmessagewas“Danger!CollisionImminent.Youhavecontrol!”.Themessagewasspokenurgentlybyafemaleactor,asifalovedonewasindanger,inlinewithEdworthyetal.(2003),andPolitisetal.(2014b,2015a).Itwasmodifiedtoremovepausesanddecreaseduration.Theresultingdurationofthemessagewas2.7sec,withapeakof-0.0dBFSandanaveragefrequencyof371Hz.ThetactileequivalentoftheaudiowarningwasaSpeechTactondeliveredwiththeELV-1411ATactor,whichwasconstructedasdescribedinPolitisetal.(2014b).Thedurationofthetactilewarningwasalso2.7sec,thepeak-0.0dBFSandtheaveragefrequency370Hz.ThevisualwarningwasthetextofthewarningdisplayedforthedurationoftheutteranceinRed(RGB(255,0,0)),asinPolitisetal.(2015b).

AllwarningsweredeliveredeitherfromthedrivingsimulatorinfrontoftheparticipantorfromaWindowstablettotherightofthedriver,aswillbedescribedbelow.Wepresentedtheabstractandlanguage-basedwarningsinallcombinationsoftheaudio,visualandtactilemodalities:Audio(A),Visual(V),Tactile(T),Audio+Visual(AV),Audio+Tactile(AT),Tactile+Visual(TV),Audio+Tactile+Visual(ATV).Asaresult28differentcueswerecreated,7cueswithallmodalities(A,T,V,AT,AV,TV,ATV)×2typesofInformation(Abstract,Language-based)×2Locations(Simulator,Tablet).Thesewarningswereevaluatedinanexperimentlookingatreactiontimesanddrivingmetricsofparticipantswhenexposedtothecues.

eXPeRIMeNT

Anexperimentwasconductedtoinvestigatehowquicklyandeffectivelyparticipantswouldbeabletoresumecontrolofanautonomouscar,whiledistractedbyagameona tablet.Weuseda tasksimilartoPolitisetal.(2015a),whereaperiodicaltransitionbacktodrivingwouldbeenforcedduetoanunexpectedcriticalevent.InlinewithPolitisetal.(2015a),weinvestigatedhowquicklyandaccuratelysuchatransitionwouldhappenandhowitwouldaffectdrivingmetrics.However,weusedonlycriticalwarningsvaryingindesign,anddeliveredfromdifferentlocations.Thereasonwasthatthefocusofthisstudywascriticalhandoversasaresultofanautomationfailure,inwhichPolitisetal.(2015a)didnotprimarilyfocus,and,asdescribedbefore,thereisverylittleresearchonhowtodesignsuchwarnings.InvestigatinghowdeliveringthecuesfromthetabletwouldimproveresultswasnotaddressedinPolitisetal.(2015a)orinanyotherstudyonthetopic.Asaresult,a7×2×2withinsubjectsdesignwasused,withModality,InformationandLocationastheindependentvariablesandResponseTime(RT),ResponseAccuracy(RA)andLateralDeviationafterHandover(LDaH)asthedependentones.AsinPolitisetal.(2015a),RTwouldbeameasureofalertnesswhenresumingdriving,RAwouldindicateanymissedresponsesandLDaHwouldshowthelevelofdistractionwhenresumingdriving(lowerLDaHwouldindicatelowerdistraction,seealsoLindgren,Angelelli,Mendoza,&Chen(2009),andLiu(2001).

Theexpectationsformingthehypothesesofthisstudywerefirstlythatthemodalitiesusedinthewarningswouldaffectresponses.AsinPolitisetal.(2015a),multimodalwarningswereexpectedtobemoreeffectivethatunimodalones,whilethevisualdisplaysonthesimulatorwereexpected tobeproblematic. In termsof Information, in linewithPolitis et al. (2015b), itwas

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expectedthatabstractcueswouldcreatequickresponses,whilelanguage-basedoneswouldaffectdrivingless.Finally,thelocationofthetabletwasexpectedtoaffectresponsespositively,sinceitwouldbelocatedintheparticipants’fieldofview,inlinewithMilleretal.(2015).Asaresult,therewerethefollowinghypotheses:

• RTwillbeinfluencedbyModality(H1a),Information(H1b)andLocation(H1c);• RAwillbeinfluencedbyModality(H2a),Information(H2b)andLocation(H2c);• LDaHwillbeinfluencedbyModality(H3a),Information(H3b)andLocation(H3c).

Participants and equipmentTwentyparticipants(7female)agedbetween20and45years(M=25.25,SD=5.67)tookpartintheexperiment.Therewere17Universitystudentsand3privateemployees.Theyhadavaliddrivinglicenseandbetween1and24yearsofdrivingexperience(M=6.18,SD=5.50).Allwererighthandedandreportednormalvisionandhearing.TheexperimenttookplaceinaUniversityroom,whereparticipantssatinfrontof27-inchDell2709Wmonitor,aPCrunningthedrivingsimulator,aMicrosoftSurfacePro32tabletPCrunningagame(placedtotherightofthedriver)andaLogitechG27gamingwheelandpedals.Thedrivingsimulatorsoftwaredepictedaruralroadscenewithacurvyroadandacarinfront,whichhasbeenusedinmanystudies,e.g.Zhao,Brumby,Chignell,Salvucci,&Goyal(2013).SeeFigure1forthesetupoftheexperiment.

The tabletwas running theConcentrationmemorygame,usedalso inPolitis et al. (2015a)andbasedonWarnock,McGhee-Lennon,&Brewster(2011)(seeFigure2b).Itwasasimplecardmatchinggameona3×8grid.Thisgamehasawell-definedsetofperformancemetricsandrequireshighlevelsofconcentration.Asitislikelythatdriverswilloccupythemselveswithotheractivitieswhileanautonomousvehicleisdrivingitself,thistaskwaschosensoastodecreasetheirengagementwithdrivingandcreateamorechallenginghandover.

Threesoundswereaddedtothegameinordertoincreaseauditorydistractions.Thefirstsoundwasa100mseclong440Hztone(noteA4) thatsoundedeverytimetheparticipant touchedthetabletscreen.Thesecondsoundwasa100msec330Hztone(noteE4)thatsoundedeverytimeapairofpicturesrevealedwasnotamatch.ThethirdonewasanEarconwiththreetones(100msecof262Hzfollowedby100msecof330Hzfollowedby100msecof392Hz–notesC4,E4,G4).Thissoundedeverytimeapairofcardswasmatched.Inthisway,anadditionalsensoryloadwascreated

Figure 1. The setup of the experiment with the tactile wristbands (a, b), the driving simulator (c) and the tablet (d)

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intheaudiomodality,whichwasnotpresentinPolitisetal.(2015a).Also,ecologicalvaliditywasincreased,sincesoundeffectsarefrequentlyfoundingames.

AuditorycuesandgamesoundsweredisplayedthroughthreeBetronportablespeakers3,onelocatedbehindthescreen(fortheSimulatorwarninglocation)twobehindthetablet(fortheTabletwarninglocationandoneforthegamesounds).Tactilecuesweredisplayedthroughawristbandonbothoftheparticipants’hands.TherighthandwasusedfortheTabletlocation,sinceitwasthehandinteractingwiththetabletandthelefthandforthesimulatorlocation,beingthehandremainingonthesteeringwheel.Pilotstudiesshowedthatthismappingwascleartoparticipantsandtheywerealsofamiliarizedwithitduringtrainingwiththecues(seebelow).VisualabstractcuesweredisplayedthroughRedcirclesthatflashedinthetopcentralareaofthemonitor(fortheSimulatorlocation,seeFigure2c)orthetablet(fortheTabletlocation,seeFigure2b),andweresized400×400pixels(about12×12cmforthemonitorand5×5cmforthetablet).Visuallanguage-basedcuesusedRedtextdisplayingthewordsfromthespeechwarning,whichappearedonceandforaslongasthewarningwasutteredinthetopcentralareaofthescreen,andwassized228×700pixels(about17×7cmforthemonitorand7×3cmforthetablet,seeFigure2d,2b).Thevisualcuesdidnotobstructtheleadcaronthemonitororthegameonthetablet.

ProcedureAfterbeingwelcomedandexplainedtheexperimentalprocedure,the28cuesweredisplayedinarandomordertoparticipantsforfamiliarization.Foreachcue,theycouldeitherrepeatitorgotothenextwhentheywerefamiliarwithit.Afterwards,theywerepresentedwiththedrivingsimulatorsoftwareandthegametofamiliarizethemselves.Inthemainexperiment,inlinewithPolitisetal.(2015a),participantswereaskedtofocusonthegame,unlessinterruptedbyawarning.Theywereabletousetheirrighthandtoplaythegameonthetablet,whichwasplacedonastandtotherightofthesimulator.Thiswouldbeastandardsetupforleft-handdrivecar.Ifallcardsinagridwerematched,

Figure 2. The driving simulator with the participant’s car in autonomous mode, as indicated visually on the top right of the screen, and the car in front driving at a safe distance (a). The tablet game with some pairs already matched, indicated in grey (b). The handover situation, where the car in front brakes suddenly and the automation fails on the same time. In this case control is handed to the driver, as indicated visually on the top right of the screen (b,c). This handover is signified through an abstract warning (the visual warning is depicted in c) or a language-based warning (the visual warning is depicted in d).

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thegamewouldreloadwithanewsetofcardschosenrandomly.Whileplayingthegame,thecarwasinautonomousmodeinthecentreofthelaneataspeedofaround60mph.ThecarsimulatedLevel3Automation(seeNHTSA(2013))notrequiringcontinuousintervention,butexpectingavailabilityforoccasionalcontrol(seeFigure2aforascreenshotofthesimulatorinautonomousmode).

Atrandomintervalsofanyintegralvaluebetween(andincluding)27–32sec(inlinewithPolitisetal.(2015a))awarningwaspresented.Inthiscase,controlwaspassedtothedriver(seeFigures2c,2d).Thissimulatedautomationfailuresthevehiclecouldnotcorrectandthereforeaswitchtomanualmodewasneeded.Tocreateamorecriticalsituation,thecarinfrontstartedbrakingatthesametimeasthepresentationofthewarning,asinPolitisetal.(2015a).Participantswerethenhandedcontrolandwereinstructedtobrakeimmediatelywiththeirrightfootandreturntosafedriving.Oncetheparticipantbraked,thecarinfrontwouldadvanceawayfromtheparticipant’scar.Itshouldbenotedthattheintervalof27–32sechadlimitedecologicalvalidity,sincecriticaleventsareexpectedtooccurlessfrequently.However,itwasfoundnecessaryinordertobeabletoevaluateallthedifferentcuesdesigned.Otherstudieshaveusedsimilarorshorterintervals,e.g.Hoetal.(2005).

To manage experimental length, all abstract warnings were presented in one block of theexperimentandalllanguage-basedonesinanother,withtheorderofblockscounterbalancedacrossparticipantsandwithasmallbreakbetweenthem.Eachwarningwaspresentedtwiceineachblock,resultinginatotalof56presentationsforbothparts(7Modalities×2typesofInformation×2Locations×2presentations).Whenbacktodriving,participantswereabletosteerusingthewheelfor10sec(therewasnoneedtousetheacceleratorpedal).

During this period, they were asked to stay in the centre of the lane. After 10 sec, the carautomaticallytookoverfromtheparticipant,initiatingthenexttrial.Onthetoprightofthescreen,acariconwouldbedisplayedwhenthecarwasinautonomousmodeorapersoniconformanualmode(seeFigure2a,2c,2d).

Responsetime(RT)wascalculatedfromtheonsetofastimulusuntiltheparticipantpressedthebrakepedal.Ifparticipantsdidnotrespondtoacue,theirresponseaccuracy(RA)was0,otherwiseitwas1.TheirLateralDeviationafterHandover(LDaH)wastheRMSEoftheirlanepositionvalues,loggedfor10secaftertheonsetofastimulusandstartofthebrakingeventoftheleadcar.Thevalueof10secwaschosensinceithasshowntobeanadequatetimetocomebacktodrivinginhandoversituations(Merat,Jamson,Lai,Daly,&Carsten,2014;Politisetal.,2015a).Theexperimentlastedabout45minutesandparticipantswerethendebriefedandpaid£6.

ReSULTS

Response TimeThedataofoneparticipantwereexcludedduetosoftwareissues.Fortherestoftheparticipantstherewere1064trialsintotal.Ifparticipantsdidnotrespondtoacue(whichwasthecasein14trials–1.3%),theirRTwasadjustedtothemaximumavailabletimetorespond,10sec,toallowathreefactorANOVAanalysis.

Data forRTwereanalysedusinga three-way repeatedmeasuresANOVA,withModality,Information and Location as factors. Due to sphericity violations, degrees of freedom werecorrectedusingGreenhouse–Geisserestimates.TherewasasignificantmaineffectofModality(F(2.11,78.19)=34.95,p<0.001).ContrastsrevealedthatVcausedslowerresponsescomparedtoallothermodalities,seeFigure3a(F(1,37)=27.42,r=0.65,p<0.001).Further,AV,AT,ATVandAcreatedquickerresponsescomparedtoTandV(F(1,37)=17.45,r=0.57,p<0.001),butnotcomparedtoTV.Asaresult,H1awasaccepted.SeeTable1forpairwisecomparisonsbetweenmodalitiesforResponseTime.TherewasasignificantmaineffectofInformation,indicatingthatabstractcuescausedfasterresponsesthanlanguagebased-ones(F(1,37)=20.50,r=0.60,p<0.001).Asa result,H1bwasaccepted.Finally, therewasasignificantmaineffectofLocation,indicatingthatwarningsfromthetabletcausedfasterreactiontimesthansimulator(F(1,37)=

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12.62,r=0.50,p<0.01).Asaresult,H1cwasaccepted.SeeTable2forvaluesofRTacrossallfactorsandFigure3aforvaluesacrossmodalities.

TherewasasignificantinteractionbetweenModalityandInformation(F(1.87,69.13)=21.04,p<0.001),indicatingthatthedisadvantageoftheVmodalitywasstrongerinlanguage-basedwarnings(F(1,37)=22.11,r=0.61,p<0.001).TherewasasignificantinteractionbetweenModalityandLocation(F(2.19,81.06)=23.14,p<0.001),indicatingthatTwarningscreatedquickerresponseswhencomingfromthesimulator(F(1,37)=7.59,r=0.41,p<0.01),whiletheobserveddisadvantageofVwarningswasstrongerwhencomingfromthesimulator(F(1,37)=33.25,r=0.69,p<0.001).TherewasasignificantinteractionbetweenInformationandLocation,indicatingthattheobserveddisadvantageoflanguage-basedcueswasstrongerwhencomingfromthesimulatorcomparedtothetablet(F(1,37)=28.30,r=0.66,p<0.001).Finally,therewasaninteractionbetweenModality,InformationandLocation(F(2.35,87.03)=19.99,p<0.001),indicatingthatwhencomingfromthesimulator,thelanguage-basedVcuesshowedadisadvantagecomparedtoTVcues,whilewhencomingfromthetablettheabstractVcuesshowedanadvantagecomparedtoTVones(F(1,37)=30.54,r=0.67,p<0.001).SeeFigure3cfortheinteractionbetweenModalityandInformationand3.efortheinteractionbetweenModalityandLocationforRT.

Response AccuracyDataforRAweretreatedasdichotomousandanalysedwithCochran’sQtests.ItwasfoundthatmodalityVwaslessaccuratecomparedtoAT,AV,TVandATV(Q(1)=11.00,p<0.01)andalsocomparedtoT(Q(1)=9.00,p<0.01)andA(Q(1)=10.00,p<0.01).Abstractcuesweremoreaccuratethanlanguage-basedones(Q(1)=8.00,p<0.01).Finally,cuesdeliveredthroughthetabletweremoreaccuratethanthesimulator(Q(1)=8.00,p<0.01).Asaresult,H2a,H2bandH2cwereaccepted.SeeTable2forvaluesofRAacrossallfactors.

Lateral DeviationTherewere1120trialsforLDaH,sincenodatawereexcludedforthismetric.DataforLDaHwereanalysedusingathree-wayrepeatedmeasuresANOVA,withModality,InformationandLocationasfactors.Duetosphericityviolations,degreesoffreedomwerecorrectedusingGreenhouse–Geisserestimates. There was a significant main effect of Modality (F(1.78,69.37) = 13.83, p < 0.001).ContrastsrevealedthatVwarningscreatedhigherLDaHvaluescomparedtoallothermodalities(F(1,39)=16.76,r=0.55,p<0.001).Asaresult,H3awasaccepted.TherewasasignificantmaineffectofInformation,revealingthatlanguage-basedwarningscreatedhigherLDaHthanabstract(F(1,39)=7.03,r=0.39,p<0.05).Asaresult,H3bwasaccepted.SeeTable3forpairwisecomparisonsbetweenmodalities forLateralDeviationafterHandover.Therewasa significantmaineffectof

Table 1. Pairwise comparisons between modalities for Response Time. The significance (p) values are reported after Bonferroni corrections.

AV AT ATV A TV T V

AV .845 .576 .689 .004 .001 .000

AT .845 .721 .700 .002 .001 .000

ATV .576 .721 .822 .009 .002 .000

A .689 .700 .822 .064 .000 .000

TV .004 .002 .009 .064 .134 .000

T .001 .001 .002 .000 .134 .000

V .000 .000 .000 .000 .000 .000

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Locationrevealingthat,whenwarningswerecomingfromthetablet,LDaHwaslowercomparedtowhencomingfromthesimulator(F(1,39)=10.18,r=0.45,p<0.01).Asaresult,H3cwasaccepted.SeeTable2forvaluesofLDaHacrossallfactorsandFigure3bforvaluesacrossmodalities.

TherewasasignificantinteractionbetweenModalityandInformation(F(1.63,63.73)=12.01,p<0.001),revealingthattheobserveddisadvantageofVwarningswasmainlypresentinlanguage-

Table 2. The mean values, of Response Time (RT), Lateral Deviation after Handover (LDaH) and Response Accuracy (RA). For RT and LDaH values in brackets indicate lower – upper 95% confidence intervals.

Measure Factor Mean

RT (sec)

Modality

A 1.03(0.88–1.18)

T 1.36(1.13–1.59)

V 2.24(1.89–2.60)

AT 1.01(0.93–1.09)

AV 1.00(0.92–1.08)

TV 1.19(1.04–1.33)

ATV 1.01(0.94–1.09)

InformationAbstract 1.11(0.98–1.23)

Language-based 1.42(1.27–1.56)

LocationSimulator 1.35(1.21–1.49)

Tablet 1.18(1.07–1.27)

LDaH (m)

Modality

A 0.96(0.67–1.24)

T 1.10(0.71–1.47)

V 2.10(1.43–2.78)

AT 0.87(0.66–1.09)

AV 0.81(0.63–0.99)

TV 0.93(0.73–1.13)

ATV 0.84(0.64–1.03)

InformationAbstract 0.94(0.68–1.21)

Language-based 1.23(0.93–1.53)

LocationSimulator 1.20(0.90–1.50)

Tablet 0.97(0.74–1.20)

RA

Modality

A 99.3%

T 98.7%

V 92.8%

AT 100%

AV 100%

TV 100%

ATV 100%

InformationAbstract 99.4%

Language-based 97.9%

LocationSimulator 97.9%

Tablet 99.4%

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basedwarnings(F(1,39)=12.11,r=0.49,p<0.01).TherewasasignificantinteractionbetweenModalityandLocation(F(1.53,59.60)=11.89,p<0.001),revealingthattheobserveddisadvantageofVwarningswasmainlypresentwhentheywerecomingfromthesimulator(F(1,39)=13.02,r=0.50,p<0.01).TherewasasignificantinteractionbetweenInformationandLocation,revealingthat theobserveddisadvantageof language-basedwarningswasmainlypresentwhen theywerecomingfromthesimulator(F(1,39)=16.25,r=0.54,p<0.001).Finally,therewasasignificantinteractionbetweenModality,InformationandLocation(F(1.76,68.80)=11.57,p<0.001),revealingthatwhileforwarningscomingfromthesimulator,modalityVcreatedhigherLDaHforlanguage-basedwarnings,whenwarningswerecomingfromthetabletthedisadvantagewasmainlypresentinlanguage-basedTcues(F(1,39)=14.92,r=0.53,p<0.001).SeeFigure3dfortheinteractionbetweenModalityandInformationand3.ffortheinteractionbetweenModalityandLocationforLDaH.

DISCUSSIoN

Theresultsoftheexperimentconfirmedtheobservedlimitationofvisuallanguage-basedcuescomingfromthesimulatorinPolitisetal.(2015a).Thesecuescreatedthelongestresponsetimes,theleastaccurateresponsesanddisturbedthedrivingthemost.However,theinterventionofthisstudy,i.e.movingthecuesfromthesimulatortothetabletandaddingabstractcuedesigns,positivelyinfluencedmetricsandaddressedtheproblemwithvisualcuesinPolitisetal.(2015a).

Response TimeAnotabledifferencetoPolitisetal.(2015a)isthelowerhandovertimesobservedinthisstudy.Thiswaspartlybecauseallhandoverswerecritical,requiringimminentattention.Anotherreasoncouldbethesimplicityofthetask,whichincontrastwithPolitisetal.(2015a)wasalwaysthesameanddidnotinvolvedifferenttypesofresponses.TheorderofmodalitiesintermsofaverageresponsetimeswassimilartoPolitisetal.(2015a),which,incombinationwiththebetterperformanceofcuesincludingaudiocomparedtounimodaltactileandvisualcues,increasesconfidenceintheadvantageofaudiocuesforsignifyinghandoversinautonomouscars.Thisextendsthefindingsofpreviousstudies(Naujoksetal.,2014;Politisetal.,2015a)byprovidingamoreelaborateexaminationofwarningmodalitiesforthissituation.Italsointroducesanextensivesetofpossiblecuestobeusedaswarningsduringanautomationfailure,extendingthecasepresentedbyGold&Bengler(2014).

Intermsofwarningdesigns,language-basedwarningsshowedadisadvantage,whichwasmainlyobservedinthesimulatorlocationandthevisualmodality.ThisconfirmsthefindingsofPolitisetal.(2015a)andonceagainshowsthattheproblemwiththevisualwarningswasamelioratedbymovingthemtotheareaofthegaminginteraction.ThisalsoextendsfindingsinPolitisetal.(2015b),where

Table 3. Pairwise comparisons between modalities for Lateral Deviation after Handover. The significance (p) values are reported after Bonferroni corrections.

AV ATV AT TV A T V

AV .512 .387 .029 .151 .059 .000

ATV .512 .641 .075 .233 .058 .000

AT .387 .641 .416 .481 .180 .000

TV .029 .075 .416 .805 .236 .000

A .151 .233 .481 .805 .265 .000

T .059 .058 .180 .236 .265 .000

V .000 .000 .000 .000 .000 .000

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abstractandlanguage-basedcuesshowedsimilarperformanceinacriticaltask.Inourstudy,weexaminedthesecueswhendeliveredfromdifferentlocationsinsimulateddriving.Itwasfoundthatabstractandlanguage-basedcuesareequallyeffectivewhencomingfromthegamelocation,whilelanguage-basedonespresentlimitationswhendeliveredawayfromit.Thisextendsfindingsofpreviousstudies(Naujoksetal.,2014;Telpazetal.,2015;Walchetal.,2015)byinvestigatingamuchwidersetofmodalitiestoinformaboutimminenthandovers.Asaguideline,inavehiclewherethedriverscouldbeinattentivetotheroadbutstillexpectedtointerveneperiodically,itwouldbeessentialtocapturetheirvisualattention.Achievingthisbyinterruptingthegameonthetabletshowedgoodresultsinourstudy.Abstractcuesalsoshowedapossibilityofcapturingattentionwhendeliveredfromthesimulator,possiblybecauseoftheirpulsatingdesign.Investigatingthisfurtherbyusing

Figure 3. (a) Mean Response Time (RT) and (b) mean Lateral Deviation after Handover (LDaH) across Modalities. (c) The interaction between Modality and Information for RT and (d) for LDaH. (e) The interaction between Modality and Location for RT and (f) for LDaH. Error bars indicate 95% confidence intervals.

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eye-trackingtechniqueswouldbepromising.Wenotethat,asinsomepreviousstudies(Politisetal.,2015a,2015b),language-basedcueswereslightlylongerandthismighthavecreatedanadvantageforabstractcues.However,reactionswererequiredimmediatelyforbothcuedesigns,andsimilarresultswereachievedforbothdesignswhencomingfromthetablet.

Afurthercommentrelatedtothelocationusedforinformingdriversisthattactilemessagesdeliveredonthehandthatwasinteractingwiththetabletshowedadisadvantagecomparedtothehandthatwasassignedforsimulatorcues.Additionally,whentactilemessagesweredeliveredincombinationwithvisualones,thebimodalpresentationwasbeneficialwhencomingfromthesimulatorforlanguage-basedcues,butproblematicwhencomingfromthetabletforabstractcues.Thefactthatcombiningvisualandtactilemodalitiesforlanguage-basedwarningsshowedanadvantagewhencomingfromthesimulator,revealsthatthisbimodalpresentationmayhavebeenclarifyingthemessagecontentwhichwasnotsalientenoughwhendeliveredonlyvisually,asinPolitisetal.(2014b).Incontrast,thelimitationofunimodaltactilepresentationfromthetabletcouldrevealunfamiliarityofthistypeofwarning,sincewechoseanovellocationforvibration,eventhoughparticipantsweretrainedwiththesecuesuntiltheyfeltconfidentwiththem.Futurestudiescouldexperimentondifferentlocationsfortabletvibrations,e.g.thefinger,andwithmoreextensivetraining.

Thelimitationsofbimodaltactileandvisualpresentationfromthetabletcouldalsorevealahighcognitiveloadwhenbeingoccupiedwithanon-drivingtaskwhilestillbeingexpectedtoperiodicallyreturntodriving.Thisisinlinewithsomeparticipants’comments,mentioningthat,evenwhenplayingthegame,theirattentionwasstillpartiallyontheroad.SimilareffectswereobservedinPolitisetal.(2014a)andinthevisualmodalitywhencombinedwithothermodalities.Sinceourstudywasamoredemandingone,requiringattentiontoboththeroadandagame,seemstohavecreatedthiseffectofincreasedattentionaldemand.InlinewithPolitisetal.(2014a),wesuggesttheuseofalimitednumberofmodalitiesinwarningsunlesstheeventtobesignifiediscritical.Evenwhencritical,whenawarningisdeliveredthroughatablet,wesuggestapreferenceforaudioandvisualmodalities.

Response AccuracyTheresultsofRAshowedthatthevisualmodalitycreatedtheleastaccurateresponses,inlinewithPolitisetal.(2015a).Abstractcuesandcuescomingfromthetabletcreatedmoreaccurateresponses,indicatingtheadvantageofaddinganewcuedesignandcuelocationcomparedtoPolitisetal.(2015a).Thisfurthersupportstheguidelineofusingtheareawhereinteractiontakesplacetowarnthedriversofimminentevents,aswellasanabstracturgentcuedesign.Itcanalsoinformdesignsofpreviousstudies(Kromeetal.,2015;Terkenetal.,2013),bycombiningagaminginteractioninthecarwithmorecriticalinterventions.Itisworthnotingthat,althoughthedescribedresultsaresignificant,theoverallRAismuchhigherthaninPolitisetal.(2015a)(1.3%ofresponseswereinaccuratehere,asopposedto9.4%inthatstudy).Thisimprovementcanbeattributedtothenewcuedesignandcuelocation,butalsotothesimplernatureoftheresponsetask.

Lateral Deviation after HandoverResultsofLDaHconfirmtheobserveddisadvantageoftheVwarningsfoundinthereactiontimeanalysis,whichisalsoinlinewithpreviousstudies(Naujoksetal.,2014;Politisetal.,2015a).Thedisadvantagewasstrongerinthesimulatorandlanguage-basedcondition,asinRT.Thisagainshowsthebenefitof thisnewsetup,which improvedLDaH,andthusreduceddriverdistractionduringcritical events requiring intervention.Whencoming from the tablet, language-based tactile cuesshowedalimitationintermsofLDaH,whichisinlinewiththeslowerresponsesobservedinRT.ThishighlightsthecautionneededwhenusingspeechTactonsunimodally,alsoobservedinotherstudies(Politisetal.,2014b,2015a,2015b).

Westressthatinthefewcaseswheretherewasanabsenceofresponse,theeffectswouldbecatastrophic.This isbecause thevehiclewouldbeuncontrolled,as theautomationfailurewouldhavedisabledautonomousdrivingandtheenforcedhandoverwouldhavebeenmissedbythedriver.

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Warningdesignersshouldaimtoeliminatesuchcasesbycreatingsalienthandoverwarningsthatwillbenoticedbydrivers.

Finally, in terms of the game performance, the results of the tablet game were as follows4:142.76secmeantimetocompleteonegame,0.45ClicksperSecondand0.27SuperfluousViewsperClick.Thesearesimilartopreviouswork(Politisetal.,2015a;Warnocketal.,2011),showingthatparticipantswereattentivetothegameandconfirmingthedemandingnatureofthistask,makingitagoodchoiceforuseindrivingexperiments.

General DiscussionAsevidentfromtheresults, thereispotentialinwarningdriversnotonlyusingtheconventionalmethodsavailableincars,butalsoattheareaofattentionfocus.Inourstudythiswasatablet,butonecaneasilyimagineotherlocationsawayfromthecentralareaofattention,suchasthecarcentrestack.Synchronisingthesedeviceswiththecarwarningmechanismwouldincreasesaliencyofwarningsandenabledriverstoreturntodrivingpromptlyinanautonomouscar.Ifthisisnotpossible,thegoodresultsobservedwithabstractwarningscomingfromthesimulatorshowsbenefitinusingmultimodalmessagestocaptureperipheralattentionincriticalsituations,asalsoobservedinSpence(2010).Thesaliencyofcuesincludingaudiocanalsobeused,bycombiningvisualandaudiowarningsintheareaofattentionfocusincriticalcases.Futureworkshoulduseshorterspeechmessagesconveyinghandoversandinvestigateiftheireffectivenesscomparedtoabstractoneswillimprove.

Toexplore further locations, futureworkshouldalsoexplicitlycompare thepresentationofwarningsonmobiledevicesversusonthecentrestack,whichisanotherpossiblelocationforplayinggamesinautonomouscars.SystemssuchasAppleCarPlay(2015)andAndroidAuto(2015a)aregainingpopularitywithusersandcarmanufacturers.Thesesystemslinkmobiledevicestocarsystemssocouldpotentiallycaptureanddisplaycarwarningsandmessagesonphonesortabletsinthecar.Thiscouldbeonadeviceusedbythedriver,orevendevicesusedbyotherpassengersthatmightbeconnectedtothecar.Ourguidelinesarerelevanttotheseapplications,aswellastoappdesignerswhoconsideranautonomouscardriverasapossiblepartoftheirusergroup.

CoNCLUSIoN

Thispaperpresentedastudyofcriticalhandoversinanautonomouscar.Participantswereoccupiedwithatabletgame,anactivityverylikelytooccurasdriversbecomelessengagedontheroadanddrivingrequireslessinvolvement.Handoversweresignifiedbymultimodalcombinationsofabstractandlanguage-basedcues.Deliveringthewarningswithabstractcuesincludingaudioandvisualsfromtheareaofthegamecapturedvisualattentionwhensignifyingahandoverofcontrol.Therefore,wesuggesttheutilisationofthisareawhenadriverisdistractedinanautonomousvehicle.Sinceinarealdrivingsituationtheremayormaynotbeasidetask,wesuggestthesynchronizationofmobiledevicesusedbythedriverwiththeautonomousvehiclesothatwarningsandnotificationsfromthecarcanbepresentedwherethedriver’sattentionisfocused,increasingwarningsaliency.

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ReFeReNCeS

Apple.(2015).CarPlay.Retrievedfromhttp://www.apple.com/uk/ios/carplay/

Baldwin,C.L.(2011).Verbalcollisionavoidancemessagesduringsimulateddriving:Perceivedurgency,alertingeffectivenessandannoyance.Ergonomics,54(4),328–337.doi:10.1080/00140139.2011.558634PMID:21491275

Edworthy,J.,Hellier,E.,Walters,K.,Clift-Mathews,W.,&Crowther,M.(2003).Acoustic,semanticandphoneticinfluencesinspokenwarningsignalwords.Applied Cognitive Psychology,17(8),915–933.doi:10.1002/acp.927

Edworthy,J.,Loxley,S.,&Dennis,I.(1991).Improvingauditorywarningdesign:Relationshipbetweenwarningsoundparametersandperceivedurgency.Human Factors: The Journal of the Human Factors and Ergonomics Society,33(2),205–231.doi:10.1177/001872089103300206PMID:1860703

Gold,C.,&Bengler,K.(2014).TakingOverControlfromHighlyAutomatedVehicles.InAdvancesinHumanAspectsofTransportation:PartII(pp.64–69).

Gold,C.,Damböck,D.,Lorenz,L.,&Bengler,K.(2013).“Takeover!”Howlongdoesittaketogetthedriverback into the loop?InHFES Annual Meeting (Vol.57,pp.1938–1942).SAGEPublications.http://doi.org/doi:<ALIGNMENT.qj></ALIGNMENT>10.1177/1541931213571433

Google.(2015a).AndroidAuto.Retrievedfromhttps://www.android.com/auto/

Google.(2015b).GoogleSelf-DrivingCarProject-Monthlyreports.Retrievedfromhttp://www.google.com/selfdrivingcar/reports/

Ho, C., Reed, N., & Spence, C. (2007). Multisensory In-Car Warning Signals for Collision Avoidance.Human Factors: The Journal of the Human Factors and Ergonomics Society , 49(6), 1107–1114.doi:10.1518/001872007X249965PMID:18074709

Ho,C.,Tan,H.Z.,&Spence,C.(2005).Usingspatialvibrotactilecuestodirectvisualattentionindrivingscenes.Transportation Research Part F: Traffic Psychology and Behaviour,8(6),397–412.doi:10.1016/j.trf.2005.05.002

Koo,J.,Kwac,J.,Ju,W.,Steinert,M.,Leifer,L.,&Nass,C.(2014).Whydidmycarjustdothat?Explainingsemi-autonomousdrivingactionstoimprovedriverunderstanding,trust,andperformance.International Journal on Interactive Design and Manufacturing.Doi:<ALIGNMENT.qj></ALIGNMENT>10.1007/s12008-014-0227-2

Krome,S.,Goddard,W.,Greuter,S.,Walz,S.P.,&Gerlicher,A.(2015).AContext-BasedDesignProcessforFutureUseCasesofAutonomousDriving:PrototypingAutoGym.ProceedingsofAutomotiveUI2015(pp.265–272).ACMPress.doi:10.1145/2799250.2799257

Kyriakidis,M.,Happee,R.,&DeWinter,J.C.F.(2014).Publicopiniononautomateddriving:Resultsofaninternationalquestionnaireamong5,000respondents.

Lee, J. D., Bricker, D. L., & Hoffman, J. D. (2008). A Dynamic Programming Algorithm for SchedulingIn-VehicleMessages.IEEE Transactions on Intelligent Transportation Systems,9(2),226–234.doi:10.1109/TITS.2008.922876

Lindgren,A.,Angelelli,A.,Mendoza,P.A.,&Chen,F.(2009).Driverbehaviourwhenusinganintegratedadvisory warning display for advanced driver assistance systems. IET Intelligent Transport Systems, 3(4),390–399.doi:10.1049/iet-its.2009.0015

Liu, Y. C. (2001). Comparative study of the effects of auditory, visual and multimodality displayson drivers’ performance in advanced traveller information systems. Ergonomics, 44(4), 425–442.doi:10.1080/00140130010011369PMID:11291824

Merat,N.,Jamson,A.H.,Lai,F.F.C.,Daly,M.,&Carsten,O.M.(2014).Transitiontomanual:Driverbehaviourwhenresumingcontrolfromahighlyautomatedvehicle.Transportation Research Part F: Traffic Psychology and Behaviour,27,274–282.doi:10.1016/j.trf.2014.09.005

Miller,D.,Sun,A.,Johns,M.,Ive,H.,Sirkin,D.,Aich,S.,&Ju,W.(2015).DistractionBecomesEngagementin Automated Driving. Proceedings of the Human Factors and Ergonomics Society Annual Meeting (pp.1676–1680).SAGE.

International Journal of Mobile Human Computer InteractionVolume 9 • Issue 3 • July-September 2017

15

Mok,B.K.,Johns,M.,Lee,K.J.,Ive,P.H.,Miller,D.,&Ju,W.(2015).TimingofUnstructuredTransitionsofControl inAutomatedDriving.Proceedings of the2015 IEEE Intelligent Vehicles Symposium (IV) (pp.1167–1172).IEEE.doi:10.1109/IVS.2015.7225841

NationalHighwayTrafficSafetyAdministration.(2013).Preliminary Statement of Policy Concerning Automated Vehicles.Washington,DC.

Naujoks,F.,Mai,C.,&Neukum,A.(2014).Theeffectofurgencyoftake-overrequestsduringhighlyautomateddrivingunderdistractionconditions.Proceedings of the 5th International Conference on Applied Human Factors and Ergonomics AHFE ‘14(pp.431–438).

Neubauer,C.,Matthews,G.,&Saxby,D.(2014).FatigueintheAutomatedVehicle:DoGamesandConversationDistractorEnergizetheDriver?Proceedings of the Human Factors and Ergonomics Society Annual Meeting(pp.2053–2057).SAGE.doi:10.1177/1541931214581432

Pfromm,M.,Khan,R.,Oppelt,S.,Abendroth,B.,&Bruder,R.(2015).InvestigationofTake-OverPerformanceofDrivingTasksbytheDriverduetoSystemFailureofSemi-AutomatedandAssistedDriving.Proceedings of the 19th Triennial Congress of the IEA(pp.1–8).

Politis, I., Brewster, S., & Pollick, F. (2013). Evaluating Multimodal Driver Displays of Varying Urgency.ProceedingsoftheAuomotiveUI‘13(pp.92–99).ACMPress;doi:10.1145/2516540.2516543

Politis,I.,Brewster,S.,&Pollick,F.(2014a).EvaluatingMultimodalDriverDisplaysunderVaryingSituationalUrgency.ProceedingsofCHI‘14(pp.4067–4076).ACMPress.doi:10.1145/2556288.2556988

Politis,I.,Brewster,S.,&Pollick,F.(2014b).SpeechTactonsImproveSpeechWarningsforDrivers.ProceedingsoftheAutomotiveUI‘14(pp.1–8).ACMPress.doi:10.1145/2667317.2667318

Politis,I.,Brewster,S.,&Pollick,F.(2015a).Language-BasedMultimodalDisplaysfortheHandoverofControlinAutonomousCars.ProceedingsoftheAutomotiveUI‘15(pp.3–10).ACMPress.doi:10.1145/2799250.2799262

Politis,I.,Brewster,S.,&Pollick,F.(2015b).ToBeeporNottoBeep?ComparingAbstractversusLanguage-BasedMultimodalDriverDisplays.ProceedingsofCHI‘15(pp.3971–3980).ACMPress.

SAE.(2002).Its In-Vehicle Message Priority StandardJ2395.

SAE J3016, & J3016, S. (2014). Taxonomy and Definitions for Terms Related to On-Road Motor Vehicle Automated Driving Systems.

Serrano,J.,DiStasi,L.L.,Megías,A.,&Catena,A.(2011).Effectofdirectionalspeechwarningsonroadhazarddetection.Traffic Injury Prevention,12(6),630–635.doi:10.1080/15389588.2011.620661PMID:22133340

Spence,C.(2010).Crossmodalspatialattention.Annals of the New York Academy of Sciences,1191(1),182–200.doi:10.1111/j.1749-6632.2010.05440.xPMID:20392281

Telpaz,A.,Rhindress,B.,Zelman,I.,&Tsimhoni,O.(2015).HapticSeatforAutomatedDriving:PreparingtheDrivertoTakeControlEffectively.Proceedings of the 7th International Conference on Automotive User Interfaces and Interactive Vehicular Applications(pp.23–30).ACMPress.doi:10.1145/2799250.2799267

Terken,Z.,Haex,R.,Beursgens,L.,&Szostak,D.(2013).UnwindingAfterWork:AnIn-CarMoodInductionSystemforSemi-AutonomousDriving.AutomotiveUI,246–249,246–249.doi:10.1145/2516540.2516571

Walch,M.,Lange,K.,Baumann,M.,&Weber,M.(2015).AutonomousDriving:InvestigatingtheFeasibilityofCar-DriverHandoverAssistanc.ProceedingsofAutomotiveUI’15(pp.11–18).ACMPress.doi:<ALIGNMENT.qj></ALIGNMENT>10.1145/2799250.2799268

Warnock,D.,McGee-Lennon,M.,&Brewster,S.(2011).TheRoleofModalityinNotificationPerformance.InInteract(pp.572–588).Springer.doi:10.1007/978-3-642-23771-3_43

Zhao,S.,Brumby,D.P.,Chignell,M.,Salvucci,D.,&Goyal,S. (2013).SharedInputMultimodalMobileInterfaces: Interaction Modality Effects on Menu Selection in Single-Task and Dual-Task Environments.Interacting with Computers,25(5),386–403.doi:10.1093/iwc/iws021

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Ioannis Politis is a Research Associate at the Engineering Design Centre, Department of Engineering, University of Cambridge. He is investigating Human-Computer Interaction topics for autonomous cars, funded by the Engineering and Physical Sciences Research Council and Jaguar - Land Rover. He completed his PhD at the University of Glasgow, Multimodal Interaction Group, funded by Freescale Semiconductor (now NXP). During his PhD, he investigated the use of multimodal displays varying in urgency and message content, to alert drivers of manual and autonomous cars. Before his PhD, he had worked as Usability Engineer at Philips Healthcare, and as Postgraduate Design Trainee at Eindhoven University of Technology.

Stephen Brewster is a Professor of Human-Computer Interaction in the School of Computing Science at the University of Glasgow, UK. He runs the internationally leading Multimodal Interaction Group. His research focuses on multimodal HCI, or using multiple sensory modalities and control mechanisms (particularly hearing, touch and gesture) to create a rich, natural interaction between human and computer. His work has a strong experimental focus, applying perceptual research to practical situations. A long term theme has been haptics, starting with force-feedback and more recently tactile displays. He has authored over 350 papers and is a member of the CHI Academy.

Frank Pollick is a professor of psychology at the University of Glasgow. He completed undergraduate studies in Physics and Biology at MIT, and masters studies in Biomedical Engineering at Case Western Reserve University before obtaining his PhD in Cognitive Sciences from The University of California, Irvine. He then moved to Kyoto, Japan where he worked at the Advanced Telecommunication Research Institute (ATR) as a researcher in the Human Information Processing laboratory. Since 1997 he has been at the University of Glasgow. His research interests include multisensory processing and how we understand the actions of others as well as how perceptual abilities change with expertise and conditions such as autism.

eNDNoTeS

1 http://www.aactechnologies.com/category/452 http://www.microsoft.com/surface/en-us/products/surface-pro-33 http://www.betrononline.com/p/9037748/betron-pop-up-portable-travel-speaker-black.html4 Themetricsusedweretakenfrom(Warnocketal.,2011)andweretheaveragetimetocompleteagame,

theclickspersecondandthesuperfluousviews.Superfluousviewsindicatehowmanydecisions(picturestapped)werenotsuccessful.Whenapicturewasvieweditwasmarkedas‘seen’.Everysubsequentviewingofthatpicturefailingtocreateamatchwasasuperfluousview.