4 Sensation and Percep.ppt

Chapter4 SensationandPerception SensationandPerception TheDistinction Sensation stimulationofsenseorgansPerception selection organization andinterpretationofsensoryinputPsychophysics thestudyofhowphysicalstimuliaretranslatedintopsychologicalexperience Fig4 1 Thedistinctionbetweensensationandperception Sensationinvolvesthestimulationofsensoryorgans whereasperceptioninvolvestheprocessingandinterpretationofsensoryinput Thetwoprocessesmergeatthepointwheresensoryreceptorsconvertphysicalenergyintoneuralimpulses Psychophysics BasicConcepts SensationbeginswithadetectablestimulusFechner theconceptofthethresholdAbsolutethreshold detected50 ofthetime Justnoticeabledifference JND smallestdifferencedetectableWeber slaw sizeofJNDproportionaltosizeofinitialstimulus Fig4 2 Theabsolutethreshold Ifabsolutethresholdsweretrulyabsolute thenatthresholdintensitytheprobabilityofdetectingastimuluswouldjumpfrom0to100 asgraphedhereinblue Inreality thechancesofdetectingastimulusincreasegraduallywithstimulusintensity asshowninred Accordingly an absolute thresholdisdefinedastheintensitylevelatwhichtheprobabilityofdetectionis50 Psychophysics ConceptsandIssues PsychophysicalScaling Fechner sLawSignal DetectionTheory Sensoryprocesses decisionprocessesSubliminalPerception Existencevs practicaleffectsSensoryAdaptation Declineinsensitivity Fig4 3 Possibleoutcomesinsignal detectiontheory Fouroutcomesarepossibleinattemptingtodetectthepresenceofweaksignals Thecriterionyousetforhowconfidentyouwanttofeelbeforereportingasignalwillaffectyourresponding Forexample ifyourequirehighconfidencebeforereportingasignal youwillminimizefalsealarms butyou llbemorelikelytomisssomesignals Vision TheStimulus Light electromagneticradiationAmplitude perceptionofbrightnessWavelength perceptionofcolorpurity mixofwavelengthsperceptionofsaturation orrichnessofcolors Fig4 5 Light thephysicalstimulusforvision a Lightwavesvaryinamplitudeandwavelength b Withinthespectrumofvisiblelight amplitude correspondingtophysicalintensity affectsmainlytheexperienceofbrightness Wavelengthaffectsmainlytheexperienceofcolor andpurityisthekeydeterminantofsaturation c Ifwhitelight suchassunlight passesthroughaprism theprismseparatesthelightintoitscomponentwavelengths creatingarainbowofcolors However visiblelightisonlythenarrowbandofwavelengthstowhichhumaneyeshappentobesensitive Fig4 6 Saturation Variationsinsaturationaredifficulttodescribe butyoucanseeexamplesfortwocolorshere TheEye ConvertingLightintoNeuralImpulses Theeye housingandchannelingComponents Cornea wherelightenterstheeyeLens focusesthelightraysontheretinaIris coloredringofmuscle constrictsordilatesviaamountoflightPupil regulatesamountoflight Fig4 7 Thehumaneye Lightpassesthroughthecornea pupil andlensandfallsonthelight sensitivesurfaceoftheretina whereimagesofobjectsarereflectedupsidedown Thelensadjustsitscurvaturetofocustheimagesfallingontheretina Thepupilregulatestheamountoflightpassingintotherearchamberoftheeye TheRetina AnExtensionoftheCNS Retina absorbslight processesimages andsendsinformationtothebrainOpticdisk wheretheopticnerveleavestheeye blindspotReceptorcells Rods blackandwhite lowlightvisionCones coloranddaylightvisionAdaptation becomingmoreorlesssensitivetolightasneededInformationprocessing ReceptivefieldsLateralantagonism Fig4 9 Theretina Thecloseupshowstheseverallayersofcellsintheretina Thecellsclosesttothebackoftheeye therodsandcones arethereceptorcellsthatactuallydetectlight Theinterveninglayersofcellsreceivesignalsfromtherodsandconesandformcircuitsthatbegintheprocessofanalyzingincominginformationbeforeitissenttothebrain Thecellsfeedintomanyopticfibers allofwhichheadtowardthe hole intheretinawheretheopticnerveleavestheeye thepointknownastheopticdisk whichcorrespondstotheblindspot PCUsers MacOS8 9 MacOSX Fig4 10 Theprocessofdarkadaptation Thedecliningthresholdsovertimeindicatethatyourvisualsensitivityisimproving aslessandlesslightisrequiredforyoutobeabletosee Visualsensitivityimprovesmarkedlyduringthefirst5to10minutesafterenteringadarkroom astheeye sbright lightreceptors thecones rapidlyadapttolowlightlevels However thecones adaptation whichisplottedinpurple soonreachesitslimit andfurtherimprovementcomesfromtherods adap tation whichisplottedinred Therodsadaptmoreslowlythanthecones buttheyarecapableoffargreatervisualsensitivityinlowlevelsoflight TheRetinaandtheBrain VisualInformationProcessing Light rodsandcones neuralsignals bipolarcells ganglioncells opticnerve opticchiasm oppositehalfbrain Mainpathway lateralgeniculatenucleus thalamus primaryvisualcortex occipitallobe magnocellular whereparvocellular whatSecondpathway superiorcolliculus thalamus primaryvisualcortex Fig4 13 Visualpathwaysthroughthebrain a Inputfromtherighthalfofthevisualfieldstrikestheleftsideofeachretinaandistransmittedtothelefthemisphere showninred Inputfromthelefthalfofthevisualfieldstrikestherightsideofeachretinaandistransmittedtotherighthemisphere showningreen Thenervefibersfromeacheyemeetattheopticchiasm wherefibersfromtheinsidehalfofeachretinacrossovertotheoppositesideofthebrain Afterreachingtheopticchiasm themajorvisualpathwayprojectsthroughthelateralgeniculatenucleusinthethalamusandontotheprimaryvisualcortex shownwithsolidlines Asecondpathwaydetoursthroughthesuperiorcolliculusandthenprojectsthroughthethalamusandontotheprimaryvisualcortex shownwithdottedlines b Thisinsetshowsaverticalviewofhowtheopticpathwaysprojectthroughthethalamusandontothevisualcortexinthebackofthebrain thetwopathwaysmappedoutindiagram a arevirtuallyindistinguishablefromthisangle Fig4 15 Thewhatandwherepathwaysfromtheprimaryvisualcortex Corticalprocessingofvisualinputisbegunintheprimaryvisualcortex Fromthere signalsareshuttledthroughthesecondaryvisualcortexandonwardtoavarietyofotherareasinthecortexalonganumberofpathways Twoprominentpathwaysarehighlightedhere Themagnocellular or wherepathway whichprocessesinformationaboutmotionanddepth movesontoareasoftheparietallobe Theparvocellular or whatpathway whichprocessesinformationaboutcolor form andtexture movesontoareasofthetemporallobe HubelandWiesel FeatureDetectorsandtheNobelPrize Early1960 s HubelandWieselMicroelectroderecordingofaxonsinprimaryvisualcortexofanimalsDiscoveredfeaturedetectors neuronsthatrespondselectivelytolines edges etc Groundbreakingresearch NobelPrizein1981Laterresearch cellsspecifictofacesinthetemporallobesofmonkeysandhumans BasicsofColorVision WavelengthdeterminescolorLonger red shorter violetAmplitudedeterminesbrightnessPuritydeterminessaturation Fig4 16 Thecolorsolid Thecolorsolidshowshowcolorvariesalongthreeperceptualdimensions brightness increasingfromthebottomtothetopofthesolid hue changingaroundthesolid sperimeter andsaturation increasingtowardtheperipheryofthesolid Fig4 17 Subtractivecolormixing Paintpigmentsselectivelyreflectspecificwavelengthsthatgiverisetoparticularcolors asyoucanseehereforblueandyellow whichbothalsoreflectbackalittlegreen Whenwemixblueandyellowpaint themixtureabsorbsallthecolorsthatblueandyellowabsorbedindividually Themixtureissubtractivebecausemorewavelengthsareremovedthanbyeachpaintalone Theyellowpaintinthemixtureabsorbsthewavelengthsassociatedwithblueandthebluepaintinthemixtureabsorbsthewavelengthsassociatedwithyellow Theonlywavelengthslefttobereflectedbackaresomeofthoseassociatedwithgreen sothemixtureisseenasgreen TheoriesofColorVision Trichromatictheory YoungandHelmholtzReceptorsforred green blue colormixingOpponentProcesstheory Hering3pairsofantagonisticcolorsred green blue yellow black whiteCurrentperspective boththeoriesnecessary Fig4 19 Thecolorcircleandcomplementarycolors Colorsoppositeeachotheronthiscolorcirclearecomplements or opposites Additivelymixingcomplementarycolorsproducesgray Opponentprocessprincipleshelpexplainthiseffectaswellastheotherpeculiaritiesofcomplementarycolorsnotedinthetext Fig4 21 Reconcilingtheoriesofcolorvision Contemporarytexplanationsofcolorvisionincludeaspectsofboththetrichromaticandopponentprocesstheories Aspredictedbytrichromatictheory therearethreetypesofreceptorsforcolor conessensitivetoshort medium andlongwavelengths However theseconesareorganizedintoreceptivefieldsthatexciteorinhibitthefiringofhigher levelvisualcellsintheretina thalamus andcortex Aspredictedbyopponentprocesstheory someofthesecellsrespondinantagonisticwaystoblueversusyellow redversusgreen andblackversuswhite PerceivingForms Patterns andObjects ReversiblefiguresPerceptualsetsInattentionalblindnessFeaturedetectiontheory bottom upprocessing Formperception top downprocessingSubjectivecontoursGestaltpsychologists thewholeismorethanthesumofitspartsReversiblefiguresandperceptualsetsdemonstratethatthesamevisualstimuluscanresultinverydifferentperceptions Fig4 24 Featureanalysisinformperception Onevigorouslydebatedtheoryofformperceptionisthatthebrainhascellsthatrespondtospecificaspectsorfeaturesofstimuli suchaslinesandangles Neuronsfunctioningashigher levelanalyzersthenrespondtoinputfromthese featuredetectors Themoreinputeachanalyzerreceives themoreactiveitbecomes Finally otherneuronsweighsignalsfromtheseanalyzersandmakea decision aboutthestimulus Inthiswayperceptionofaformisarrivedatbyassemblingelementsfromthebottomup Fig4 25 Bottom upversustop downprocessing Asexplainedinthesediagrams bottom upprocessingprogressesfromindividualelementstowholeelements whereastop downprocessingprogressesfromthewholetotheindividualelements PrinciplesofPerception Gestaltprinciplesofformperception figure ground proximity similarity continuity closure andsimplicityRecentresearch Distal stimulioutsidethebody vs proximal stimulusenergiesimpingingonsensoryreceptors stimuli PerceptualhypothesesContext Fig4 27 Theprincipleoffigureandground Whetheryouseetwofacesoravasedependsonwhichpartofthisdrawingyouseeasfigureandwhichasbackground Althoughthisreversibledrawingallowsyoutoswitchbackandforthbetweentwowaysoforganizingyourperception youcan tperceivethedrawingbothwaysatonce Fig4 28 Gestaltprinciplesofperceptualorganization Gestaltprincipleshelpexplainhowpeoplesubjectivelyorganizeperception a Proximity Thesedotsmightwellbeorganizedinverticalcolumnsratherthanhorizontalrows butbecauseofproximity thedotsareclosertogetherhorizontally theytendtobeperceivedinrows b Closure Eventhoughthefiguresareincomplete youfillintheblanksandseeacircleandadog c Similarity Becauseofsimilarityofcolor youseedotsorganizedintothenumber2insteadofarandomarray Ifyoudidnotgroupsimilarelements youwouldn tseethenumber2here d Simplicity Youcouldviewthisasacomplicated11 sidedfigure butgiventhepreferenceforsimplicity youaremorelikelytoseeitasarectangleandatriangle e Continuity Youtendtogroupthesedotsinawaythatproducesasmoothpathratherthananabruptshiftindirection Fig4 29 Distalandproximalstimuli Proximalstimuliareoftendistorted shiftingrepresentationsofdistalstimuliintherealworld Ifyoulookdirectlydownatasmall squarepieceofpaperonadesk a thedistalstimulus thepaper andtheproximalstimulus theimageprojectedonyourretina willbothbesquare Butasyoumovethepaperawayonthedesktop asshownin b and c thesquaredistalstimulusprojectsanincreasinglytrapezoidalimageonyourretina makingtheproximalstimulusmoreandmoredistorted Nevertheless youcontinuetoperceiveasquare Fig4 30 Afamousreversiblefigure Whatdoyousee Consultthetexttolearnwhatthetwopossibleinterpretationsofthisfigureare Fig4 31 TheNeckercube Thetintedsurfaceofthisreversiblefigurecanbecomeeitherthefrontorthebackofthecube Fig4 33 Contexteffects Thecontextinwhichastimulusisseencanaffectyourperceptualhypotheses DepthandDistancePerception Binocularcues cluesfrombotheyestogetherretinaldisparityconvergenceMonocularcues cluesfromasingleeyemotionparallaxaccommodationpictorialdepthcues StabilityinthePerceptualWorld PerceptualConstancies Perceptualconstancies stableperceptionsamidchangingstimuliSizeShapeBrightnessHueLocationinspace OpticalIllusions ThePowerofMisleadingCues OpticalIllusions discrepancybetweenvisualappearanceandphysicalrealityFamousopticalillusions Muller LyerIllusion PonzoIllusion PoggendorfIllusion Upside DownTIllusion ZollnerIllusion theAmesRoom andImpossibleFiguresCulturaldifferences Perceptualhypothesesatwork PCUsers MacOS8 9 MacOSX Fig4 38 TheM ller Lyerillusion Goahead measurethem thetwoverticallinesareofequallength Fig4 39 ExplainingtheM ller Lyerillusion Thefigureontheleftseemstobecloser sinceitlookslikeanoutsidecorner thrusttowardyou whereasthefigureontherightlookslikeaninsidecornerthrustawayfromyou Givenretinalimagesofthesamelength youassumethatthe closer lineisshorter Fig4 43 Threeclassicimpossiblefigures Thefiguresareimpossible yettheyclearlyexist onthepage Whatmakesthemimpossibleisthattheyappeartobethree dimensionalrepresentationsyetaredrawninawaythatfrustratesmentalattemptsto assemble theirfeaturesintopossibleobjects It sdifficulttoseethedrawingssimplyaslineslyinginaplane eventhoughthisperceptualhypothesisistheonlyonethatresolvesthecontradiction Hearing TheAuditorySystem Stimulus soundwaves vibrationsofmoleculestravelinginair Amplitude loudness Wavelength pitch Purity timbre Wavelengthdescribedintermsoffrequency measuredincyclespersecond Hz Frequencyincrease pitchincrease Fig4 45 Sound thephysicalstimulusforhearing a Likelight soundtravelsinwaves inthiscase wavesofairpressure Asmoothcurvewouldrepresentapuretone suchasthatproducedbyatuningfork Mostsounds however arecomplex Forexample thewaveshownhereisformiddleCplayedonapiano Thesoundwaveforthesamenoteplayedonaviolinwouldhavethesamewavelength orfrequency asthisone butthe wrinkles inthewavewouldbedifferent correspondingtothedifferencesintimbrebetweenthetwosounds b Thetableshowsthemainrelationsbetweenobjectiveaspectsofsoundandsubjectiveperceptions TheEar ThreeDivisions Externalear pinna collectssound Middleear theossicles hammer anvil stirrup Innerear thecochleaafluid filled coiledtunnelcontainsthehaircells theauditoryreceptorslineduponthebasilarmembrane Fig4 47 Thehumanear Convertingsoundpressuretoinformationprocessedbythenervoussysteminvolvesacomplexrelayofstimuli Wavesofairpressurecreatevibrationsintheeardrum whichinturncauseoscillationsinthetinybonesintheinnerear thehammer anvil andstirrup Astheyarerelayedfromonebonetothenext theoscillationsaremagnifiedandthentransformedintopressurewavesmovingthroughaliquidmediuminthecochlea Thesewavescausethebasilarmembranetooscillate stimulatingthehaircellsthataretheactualauditoryreceptors seeFigure4 48 Fig4 48 Thebasilarmembrane Thefigureshowsthecochleaunwoundandcutopentorevealthebasilarmembrane whichiscoveredwiththousandsofhaircells theauditoryreceptors Pressurewavesinthefluidfillingthecochleacauseoscillationstotravelinwavesdownthebasilarmembrane stimulatingthehaircellsto re Althoughtheentiremembranevibrates aspredictedbyfrequencytheory thepointalongthemembranewherethewavepeaksdependsonthefrequencyofthesoundstimulus assuggestedbyplacetheory TheAuditoryPathway SoundwavesvibratebonesofthemiddleearStirruphitsagainsttheovalwindowofcochleaSetsthefluidinsideinmotionHaircellsarestimulatedwiththemovementofthebasilarmembranePhysicalstimulationconvertedintoneuralimpulsesSentthroughthethalamustotheauditorycortex temporallobes TheoriesofHearing PlaceorFrequency HermannvonHelmholtz 1863 PlacetheoryOtherresearchers Rutherford 1886 FrequencytheoryGeorgvonBekesy 1947 Travelingwavetheory AuditoryLocalization WhereDidthatSoundComeFrom Twocuescritical Intensity loudness TimingofsoundsarrivingateachearHeadas shadow orpartialsoundbarrierTimingdifferencesassmallas1 100 000ofasecond Fig4 49 Cuesinauditorylocalization Asoundcomingfromtheleftreachestheleftearsoonerthantheright Whenthesoundreachestherightear itisalsolessintensebecauseithastraveledagreaterdistanceandbecauseitisinthesoundshadowproducedbythelistener shead Thesecuesareusedtolocalizethesourcesofsoundinspace TheChemicalSenses Taste Taste gustation Physicalstimulus solublechemicalsubstancesReceptorcellsfoundintastebudsPathway tastebuds neuralimpulse thalamus cortexFourprimarytastes sweet sour bitter andsaltyTaste learnedandsocialprocesses Fig4 50 Thetongueandta