Depth Perception - Vivid Vision

Depth perception arises from a variety of depth cues. These are typically classified into binocular cues that are based on the receipt of sensory information in ... REGISTER LOGIN ENGLISH ENGLISH DEUTSCH 日本語 中文 HELP BLOG SetupVividVisionHome DepthPerception Depthperceptionisthevisualabilitytoperceivetheworldinthreedimensions(3D)andthedistanceofanobject.Depthsensationisthecorrespondingtermforanimals,sincealthoughitisknownthatanimalscansensethedistanceofanobject(becauseoftheirabilitytomoveaccuratelyortorespondconsistently,accordingtothatdistance),itisnotknownwhetherthey"perceive"itinthesamesubjectivewaythathumansdo Depthperceptionarisesfromavarietyofdepthcues.Thesearetypicallyclassifiedintobinocularcuesthatarebasedonthereceiptofsensoryinformationinthreedimensionsfrombotheyesandmonocularcuesthatcanberepresentedinjusttwodimensionsandobservedwithjustoneeye.[2][3]Binocularcuesincludestereopsis,eyeconvergence,disparity,andyieldingdepthfrombinocularvisionthroughexploitationofparallax.Monocularcuesincludesize:distantobjectssubtendsmallervisualanglesthannearobjects,grain,size,andmotionparallax. Monocularcues Motionparallax Whenanobservermoves,theapparentrelativemotionofseveralstationaryobjectsagainstabackgroundgiveshintsabouttheirrelativedistance.Ifinformationaboutthedirectionandvelocityofmovementisknown,motionparallaxcanprovideabsolutedepthinformation.[5]Thiseffectcanbeseenclearlywhendrivinginacar.Nearbythingspassquickly,whilefaroffobjectsappearstationary.Someanimalsthatlackbinocularvisionduetotheireyeshavinglittlecommonfield-of-viewemploymotionparallaxmoreexplicitlythanhumansfordepthcueing(e.g.,sometypesofbirds,whichbobtheirheadstoachievemotionparallax,andsquirrels,whichmoveinlinesorthogonaltoanobjectofinteresttodothesame Depthfrommotion Whenanobjectmovestowardtheobserver,theretinalprojectionofanobjectexpandsoveraperiodoftime,whichleadstotheperceptionofmovementinalinetowardtheobserver.Anothernameforthisphenomenonisdepthfromopticalexpansion.Thedynamicstimuluschangeenablestheobservernotonlytoseetheobjectasmoving,buttoperceivethedistanceofthemovingobject.Thus,inthiscontext,thechangingsizeservesasadistancecue.Arelatedphenomenonisthevisualsystem’scapacitytocalculatetime-to-contact(TTC)ofanapproachingobjectfromtherateofopticalexpansion–ausefulabilityincontextsrangingfromdrivingacartoplayingaballgame.However,calculationofTTCis,strictlyspeaking,perceptionofvelocityratherthandepth. Kineticdeptheffect Ifastationaryrigidfigure(forexample,awirecube)isplacedinfrontofapointsourceoflightsothatitsshadowfallsonatranslucentscreen,anobserverontheothersideofthescreenwillseeatwo-dimensionalpatternoflines.Butifthecuberotates,thevisualsystemwillextractthenecessaryinformationforperceptionofthethirddimensionfromthemovementsofthelines,andacubeisseen.Thisisanexampleofthekineticdeptheffect.Theeffectalsooccurswhentherotatingobjectissolid(ratherthananoutlinefigure),providedthattheprojectedshadowconsistsoflineswhichhavedefinitecornersorendpoints,andthattheselineschangeinbothlengthandorientationduringtherotation. Perspective Thepropertyofparallellinesconverginginthedistance,atinfinity,allowsustoreconstructtherelativedistanceoftwopartsofanobject,oroflandscapefeatures.Anexamplewouldbestandingonastraightroad,lookingdowntheroad,andnoticingtheroadnarrowsasitgoesoffinthedistance. Relativesize Iftwoobjectsareknowntobethesamesize(e.g.,twotrees)buttheirabsolutesizeisunknown,relativesizecuescanprovideinformationabouttherelativedepthofthetwoobjects.Ifonesubtendsalargervisualangleontheretinathantheother,theobjectwhichsubtendsthelargervisualangleappearscloser. Familiarsize Sincethevisualangleofanobjectprojectedontotheretinadecreaseswithdistance,thisinformationcanbecombinedwithpreviousknowledgeoftheobject'ssizetodeterminetheabsolutedepthoftheobject.Forexample,peoplearegenerallyfamiliarwiththesizeofanaverageautomobile.Thispriorknowledgecanbecombinedwithinformationabouttheangleitsubtendsontheretinatodeterminetheabsolutedepthofanautomobileinascene. Absolutesize Eveniftheactualsizeoftheobjectisunknownandthereisonlyoneobjectvisible,asmallerobjectseemsfurtherawaythanalargeobjectthatispresentedatthesamelocation Aerialperspective Duetolightscatteringbytheatmosphere,objectsthatareagreatdistanceawayhavelowerluminancecontrastandlowercolorsaturation.Duetothis,imagesseemhazythefarthertheyareawayfromaperson'spointofview.Incomputergraphics,thisisoftencalled"distancefog".Theforegroundhashighcontrast;thebackgroundhasalowcontrast.Objectsdifferingonlyintheircontrastwithabackgroundappeartobeatdifferentdepths.Thecolorofdistantobjectsarealsoshiftedtowardtheblueendofthespectrum(e.g.,distantmountains).Somepainters,notablyCézanne,employ"warm"pigments(red,yellowandorange)tobringfeaturesforwardtowardstheviewer,and"cool"ones(blue,violet,andblue-green)toindicatethepartofaformthatcurvesawayfromthepictureplane. Accommodation Thisisanoculomotorcuefordepthperception.Whenwetrytofocusonfarawayobjects,theciliarymusclesstretchtheeyelens,makingitthinner,andhencechangingthefocallength.Thekinestheticsensationsofthecontractingandrelaxingciliarymuscles(intraocularmuscles)issenttothevisualcortexwhereitisusedforinterpretingdistance/depth.Accommodationisonlyeffectivefordistanceslessthan2meters. Occultation Occultation(alsoreferredtoasinterposition)happenswhennearsurfacesoverlapfarsurfaces.Ifoneobjectpartiallyblockstheviewofanotherobject,humansperceiveitascloser.However,thisinformationonlyallowstheobservertocreatea"ranking"ofrelativenearness.Thepresenceofmonocularambientocclusionsconsistsoftheobject'stextureandgeometry.Thesephenomenaareabletoreducethedepthperceptionlatencybothinnaturalandartificialstimuli. Curvilinearperspective Attheouterextremesofthevisualfield,parallellinesbecomecurved,asinaphototakenthroughafisheyelens.Thiseffect,althoughitisusuallyeliminatedfrombothartandphotosbythecroppingorframingofapicture,greatlyenhancestheviewer'ssenseofbeingpositionedwithinareal,three-dimensionalspace.(Classicalperspectivehasnouseforthisso-called"distortion,"althoughinfactthe"distortions"strictlyobeyopticallawsandprovideperfectlyvalidvisualinformation,justasclassicalperspectivedoesforthepartofthefieldofvisionthatfallswithinitsframe.) Texturegradient Finedetailsonnearbyobjectscanbeseenclearly,whereassuchdetailsarenotvisibleonfarawayobjects.Texturegradientsaregrainsofanitem.Forexample,onalonggravelroad,thegravelneartheobservercanbeclearlyseenofshape,size,andcolor.Inthedistance,theroad'stexturecannotbeclearlydifferentiated. Lightingandshading Thewaythatlightfallsonanobjectandreflectsoffitssurfaces,andtheshadowsthatarecastbyobjectsprovideaneffectivecueforthebraintodeterminetheshapeofobjectsandtheirpositioninspace. Defocusblur Selectiveimageblurringisverycommonlyusedinphotographicandvideoforestablishingtheimpressionofdepth.Thiscanactasamonocularcueevenwhenallothercuesareremoved.Itmaycontributetothedepthperceptioninnaturalretinalimagesbecausethedepthoffocusofthehumaneyeislimited.Inaddition,thereareseveraldepthestimationalgorithmsbasedondefocusandblurring.Somejumpingspidersareknowntouseimagedefocustojudgedepth. Elevation Whenanobjectisvisiblerelativetothehorizon,wetendtoperceiveobjectswhichareclosertothehorizonasbeingfartherawayfromusandobjectswhicharefartherfromthehorizonasbeingclosertous.Inaddition,ifanobjectmovesfromapositionclosethehorizontoapositionhigherorlowerthanthehorizon,itwillappeartomoveclosertotheviewer. Binocularcues Stereopsis,orretinal(binocular)disparity,orbinocularparallax Animalsthathavetheireyesplacedfrontallycanalsouseinformationderivedfromthedifferentprojectionofobjectsontoeachretinatojudgedepth.Byusingtwoimagesofthesamesceneobtainedfromslightlydifferentangles,itispossibletotriangulatethedistancetoanobjectwithahighdegreeofaccuracy.Eacheyeviewsaslightlydifferentangleofanobjectseenbytheleftandrighteyes.Thishappensbecauseofthehorizontalseparationparallaxoftheeyes.Ifanobjectisfaraway,thedisparityofthatimagefallingonbothretinaswillbesmall.Iftheobjectiscloseornear,thedisparitywillbelarge.ItisstereopsisthattrickspeopleintothinkingtheyperceivedepthwhenviewingMagicEyes,Autostereograms,3-Dmovies,andstereoscopicphotos. Convergence Thisisabinocularoculomotorcuefordistance/depthperception.Becauseofstereopsis,thetwoeyeballsfocusonthesameobject.Indoingsotheyconverge.Theconvergencewillstretchtheextraocularmuscles.Ashappenswiththemonocularaccommodationcue,kinestheticsensationsfromtheseextraocularmusclesalsohelpin-depth/distanceperception.Theangleofconvergenceissmallerwhentheeyeisfixatingonfarawayobjects.Convergenceiseffectivefordistanceslessthan10meters. ShadowStereopsis AntonioMedinaPuertademonstratedthatretinalimageswithnoparallaxdisparitybutwithdifferentshadowsarefusedstereoscopically,impartingdepthperceptiontotheimagedscene.Henamedthephenomenon"shadowstereopsis".Shadowsarethereforeanimportant,stereoscopiccuefordepthperception. Disordersaffectingdepthperception Ocularconditionssuchasamblyopia,opticnervehypoplasia,andstrabismusmayreducetheperceptionofdepth. Since(bydefinition),binoculardepthperceptionrequirestwofunctioningeyes,apersonwithonlyonefunctioningeyehasnobinoculardepthperception. Depthperceptionmustbelearnedusinganunconsciousinference,whichismuchlesslikelytohappenafterafewyearsofage References: Howard,Ian(2012).PerceivinginDepth.NewYork:OxfordUniversityPress.ISBN978-0-199-76414-3. Sternberg,R.K.(2012). GoldsteinE.B.(2014,2017)Sensationandperception(10thed.).PacificGroveCA:Wadsworth. FindaVividVisionProvider Over465VividVisionProvidersprescribevirtualrealityalongsidepatchingandvisiontherapytotreatyourlazyeye.SignupthroughourdoctorlocatortoseeifVividVisionisrightforyou. 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