Force constancy and its effect on haptic perceptio

ForceConstancyandItsEffectonHapticPerceptionofVirtualSurfacesSEUNGMOONCHOI,LARONWALKER,andHONGZ.TANHapticInterfaceResearchLaboratory,PurdueUniversityandSCOTTCRITTENDENandRONREIFENBERGERNanophysicsLaboratory,PurdueUniversityTheforce-constancyhypothesisstatesthattheuserofaforce-feedbackdevicemaintainsaconstantpenetrationforcewhenstrokingvirtualsurfacesinordertoperceivetheirtopography.Thehypothesiswasdevelopedtoaddressareal-worlddataperceptualizationproblemwheretheperceptionofsurfacetopographywasdistortedwhenthesurfacestiffnesswasnonuniform.Twoexperimentswereconducted.InExperimentI,werecordedthepenetrationdepthsoftheprobetipwhiletheuserstrokedtwosurfaceswithequalheightbutdifferentstiffnessvalues.Wefoundthatthedatacouldbequantitativelymodeledbytheforce-constancyhypothesiswhenthevirtualsurfaceswereneithertoosoftnortoohard.InExperimentII,wedemonstratedthatgiventwoadjacentsurfaces,theirperceivedheightdifferencedependedonboththesurfacestiffnessvaluesaswellastherelativeheightsofthesurfaces.Specifically,weshowedthatthehigherbutsoftersurfacecouldbeperceivedtobelower,atthesameheight,orhigherthantheothersurface,dependingonhowmuchhigheritwasthantheothersurface.Theresultswereconsistentwiththepredictionsoftheforce-constancyhypothesis.Ourfindingsunderscoretheimportanceofunderstandingtheinterplayofhapticrenderingparameters.CategoriesandSubjectDescriptors:H.1.2[ModelsandPrinciples]:User/MachineSystems—humaninformationprocessing;H.5.1[InformationInterfacesandPresentation]:MultimediaInformationSystems—artificial,augmented,andvirtualre-alities;H.5.2[InformationInterfacesandPresentation]:UserInterfaces—evaluation/methodology;HapticI/OGeneralTerms:Experimentation,Theory,VerificationAdditionalKeyWordsandPhrases:Hapticrendering,forceconstancy,surfacetopography,psychophysics1.INTRODUCTIONThispaperisconcernedwithhowusersinteractwithahapticvirtualsurfaceandhowtheinteractionstrategyaffectstheperceptionofsurfaceproperties.Giventhatmostforce-feedbackhapticinterfacesareThisworkwassupportedinpartbyaNationalScienceFoundation(NSF)FacultyEarlyCareerDevelopment(CAREER)awardundergrantno.9984991-IIS,anNSFawardundergrantno.0098443-IIS,aNASAawardundergrantno.NCC2-1363,andtheBirckNanotechnologyCenteratPurdueUniversity.ThefirstauthorwaspartiallysupportedbytheEnvisionCenterforDataPerceptualizationatPurdueUniversity.ThesecondauthorwaspartiallysupportedbyaGAANN(GraduateAssistanceinAreasofNationalNeed)Fellowship.Authors’addresses:SeungmoonChoi,LaronWalker,HongZ.Tan,HapticInterfaceResearchLaboratory,465NorthwesternAvenue,WestLafayette,IN47907-2035;emails:{chois,walkerla,hongtan}@purdue.edu;ScottCrittenden,RonReifenberger,NanophysicsLaboratory,DepartmentofPhysics,PurdueUniversity,WestLafayette,IN47907;emails:{scott,rr}@physics.purdue.edu.Permissiontomakedigitalorhardcopiesofpartorallofthisworkforpersonalorclassroomuseisgrantedwithoutfeeprovidedthatcopiesarenotmadeordistributedforprofitordirectcommercialadvantageandthatcopiesshowthisnoticeonthefirstpageorinitialscreenofadisplayalongwiththefullcitation.CopyrightsforcomponentsofthisworkownedbyothersthanACMmustbehonored.Abstractingwithcreditispermitted.Tocopyotherwise,torepublish,topostonservers,toredistributetolists,ortouseanycomponentofthisworkinotherworksrequirespriorspecificpermissionand/orafee.PermissionsmayberequestedfromPublicationsDept.,ACM,Inc.,1515Broadway,NewYork,NY10036USA,fax:[phone],[e-mail].c
2005ACM1544-3558/05/0400-0089$5.00ACMTransactionsonAppliedPerception,Vol.2,No.2,April2005,Pages89–105.90•S.Choietal.Fig.1.Anillustrationofasurfaceprofile(solidline)andthetrajectoryfollowedbytheprobetip(dashedline)whenthesurfaceisexploredwithahapticdevice.basedondiscretecontactpoint(s),werestrictourstudytoprobe-mediatedhapticsurfaceexploration.Weobservethatthewaypeopleinteractwithavirtualsurfaceisfundamentallydifferentfromthatwitharealsurfacewhenthesurfacesarereasonablyhardtothetouch.Duringexplorationofarealsurface,theinterfaceproberemainsincontactwiththesurfacebutneverpenetratesit.Wheninteractingwithavirtualsurface,however,mosthapticrenderingmethodsrequiretheusertopushtheprobeintothevirtualsurfacebeforeafeedbackforcecanbegenerated.Thisresistancetopenetrationisthenattributedtotheexistenceofasurfacebytheuser.Inboththerealandvirtualenvironments,theuserformsamentalimageofthesurfacetopographybasedontheperceivedtrajectoryoftheprobetip.Itfollowsthatthetrajectoryoftheprobetipmustbeparalleltothatofthevirtualsurfaceinorderfortheusertoperceivethesurfacetopographycorrectly,albeitatanoffsetinspace(seeFigure1).Whenthetrajectoryoftheprobetipceasestobeparalleltothevirtualsurface,theuser’sperceptionofthesurfacetopographyisdistorted.Thiscanbeaseriousproblemwhenthevirtualsurfaceisbeingrenderedforscientificdatavisualizationorperceptualization.Whenthesurfacesareverysoft(e.g.,softfoams,cottonballs),however,theirsurfacetopographycannotbeaccuratelyperceivedbyaprobeineitherarealorvirtualenvironment.Thelackofinitialcontactcuesorsufficientresistanceforcesmakesitdifficulttodiscernwheretheprobeisrelativetotheobjectsurfaces.Asw