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Chapter 9

PSYC 303 Chapter Notes - Chapter 9: Stereoscope, Diplopia, Stereopsis


Department
Psychology
Course Code
PSYC 303
Professor
Thomas Spalek
Chapter
9

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TypesofDepthPerception
Absolutedistance:perceptionoftheactualdistanceofanobject(eg.howfarawayapencil
isonadesk)
Egocentriclocalization:whereourbodiesarepositionedrelativetootherobjectsinthe
externalenvironment
Objectrelativelocalizations:perceptionofrelativedistance/estimatesofdistances
betweenobjectsintheenvironment(eg.isthepencillyingnearertothebookorcoffeemug
alsoonthedesk)
● alsowhetherornotanobjectis2Dor3D
Directperception:threeassumptions
● alltheinformationweneedtoseein3Dispresentintheretinalimageorin
relationshipsamongpartsoftheretinalimage
● thevisualsceneisanalysedbythebrainintermsofwholeobjectsandsurfaces
ratherthanintermsofelementarystimulussuchasedges,color,andspecific
locationsthatmakeupobjects
● assumestheimpressionofdepthordistancearisesimmediatelyintheobserveron
viewingthestimulusandneedsnofurthercomputationoranyadditionalinformation
basedoninterferesorexperiences
Artificialintelligence:apartofcomputersciencethatattemptstodesignmachinesthat
believeintelligently,suchasmachinesthatcaninterpretvisualinformation
● onetypeofscientistisinterestedindesigningrobotsthatcanperformtasksfor
humanbasedonvisualinput
● secondtypeisinterestedindesigningsoftwarethatwillduplicatetheprocessing
stepsactuallyusedbyhumanobserverswhenviewingvisualstimulisuchaspictures
○ thesecondtypeisreferredtocomputationaltheoriesofvision
DavidMarr
● startedwithdirectperception;butlatersuggestedaccurateinterpretationof3D
requirescomplexcalculationsandseveralstagesofanalysis.
Modularityofperception:JerryFodor(1983);viewedthemindasadistinctsetofunitsor
modules,eachofwhichiscompleteinitselfandhasaspecificfunctionwithdedicatedneural
hardwarethatcandoaspecificbitofprocessingorcomputation
● allowsperceptiontobequickwithoutconsciousintervention
● outputofmanymodulescanbegatheredandpassedtohigherprocessingcenters
Intelligentperception:Helmholtz(1867);perceptionoftheworldismuchricherandmore
accuratethanmightbeexpectedonthebasisofinformationcontainedinthevisualimage
alone
ConstructiveTheories:thecombiningofseveralsourcesofinformationtobuildor
assembleofourconsciousexperience

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PictorialDepthCues
Cue:signalsinthestimulusthatwenotoftennotconsciouslyawareof,butthatfunctionto
shapeourperceptualresponses
Pictorialdepthcues:impressionsofrelativedistances
Monocularcues:cuesthatareavailablewhenonlyoneeyeisbeingusedtoviewascene
InterpositionorOcclusion
Interposition/Occlusion:closerobjectblockoutfurtherobjects;lightreflectedfromdistant
objectscannotpassthroughopaqueobjectsthatstandbetweenthemandtheobserver
Cuesforocclusioncanbeglobal,buttherearesubtlecluesforlocalcues:
Tjunction:asmooth,continuouscontouragainstwhichanothercontourabruptlyends(can
alsobeYorLshaped)
“Filling”inofoccludedpartisveryrapidandautomatic.
● 100200ms;increasingthenumberandqualityofdepthcuesinthescenecan
reducetimeto>100ms
Amodalcompletion:themissingpartsofthefigureareperceptuallypresenteventhough
therearenophysicalstimulitosupportthatconclusion
● preferencetofillinwiththesimplest,regularobject(pragnanz)
ShadingandShadows
Shadows:concave/convex(pimplevs.dimple);indicatorofwherelightcomesfrom
● pimple:whitetoblack;dimple:blacktowhite
Thevisualsystemhasadoptedtheassumptionthatalightsourceisusuallyabovethehead,
ratherthan(themoreaccurate)ofbeingabovetheground.
● AreaV4ofthecortexlinksthedepthinterpretationtoretinalcoordinates
● specificneuronsfoundthatappeartobeselectivelytunedforbrightnesspatterns
withshadowsontopsversusshadowsonthebottom
Attachedshadows:givesinformationaboutshape;definestheshapeofanobject
● distributedovertheobject
Castshadows:whereobjectisrelativetosurface
● themoreseparateditisfromtheshadow,thegreaterthedistance
Bothtypesofshadows:
● fallawayfromthesourceoflight(direction)
● aredarkerthanthesurfacesonwhichtheyareprojected(brightness)
AerialPerspective
Theairisfilledwithlightabsorbingandlightscatteringparticles.
● shorterwavelengths(blue)arescatteredmorethanlongerones

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Aerialperspective:theimageofaverydistantobject,suchasadistantmountain,willbe
slightlybluerinhueandhazierorlessdistinctinappearancethantheimagesofnearer
objectsthatarephysicallythesamecolor
● dryairreducesaerialperspective;objectivesonawetmorningseemfurtherthanon
adryafternoon
Relativebrightness/contrast:thelightfrommoredistantobjectsmusttravelthroughthe
atmosphereforagreaterdistanceandmaybesubjecttoincreasedabsorptionorscattering
oflight
● moredistantobjectappearslessbright
RetinalandFamiliarSize
Retinalimagesize:asanobjectmovesfurtheraway,theimagesizeisreduced;biggeris
closer
● usedbybothdirectperceptionandcomputationaltheories
Familiarsize:estimatinghowfarimageisaway;buthassomepriorknowledgeabout
objects(eg.sizeofcoins)
● constructivisttheories
Reductionconditions:darkenedroomwithallotherdepthduesremoved
LinearPerspective
Linearperspective:extensionofretinalimagesizecue
● parallellinesconvergeandobjectsgetsmallerinasystematicfashionastheir
distancesincrease
Vanishingpoint:whereallperspectivelinesconvergeandobjectsdiminishtoinvisibility
● usuallyonthehorizon
TextureGradients
Texturegradient:JamesGibson;avisualtextureislooselydefinedasanycollectionof
objectsinthevisualimage;thegradient(continuouschange)isthechangeintherelative
sizeandcompactnessoftheseobjectelements
● themoredistantpartsofatexturehavesmallerelementsthataremoredensely
packedtogether
● canarguethattexturegradientsarecombinationofrelativesize,heightinplane,and
perspective
Detailperspective:thedepthimpressionassociatedwithtexturegradients
● suddenchangesintexturesusuallysignalachangeindirectionofdistanceofa
surface
● globalperspective
HeightinthePlane
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