Psy 280: PerceptionPsy 280: Perception

Prof. AndersonProf. AndersonDepartment of PsychologyDepartment of Psychology

Week 2Week 2

Part 1: Part 1: The process of perceptionThe process of perception

Martians on earth?Martians on earth?2 front facing spherical sensors2 front facing spherical sensors

Light reactive chemicalLight reactive chemical2 fleshy antennae on side of 2 fleshy antennae on side of headhead

Pressure sensitive hairsPressure sensitive hairsCutaneous membraneCutaneous membrane

Little detectors of different Little detectors of different shapesshapes

Temperature, pain, caressTemperature, pain, caress

Bilateral air holesBilateral air holesChemical sampling of gasesChemical sampling of gases

Retractable probeRetractable probeChemical sampling of solids, Chemical sampling of solids, liquids liquids

Perception is easyPerception is easyMisleadingMisleadingWorld is projected on retina World is projected on retina ——> > ““visionvision””

Discovery of depth in art, but not perception of depthDiscovery of depth in art, but not perception of depth

Computer visionComputer visionMIT student summer projectMIT student summer project

No privileged access to how No privileged access to how perception worksperception works

Perception is not just about introspectionPerception is not just about introspectionCanCan’’t introspect about working of the brain t introspect about working of the brain directlydirectlyHave access to the results of complex Have access to the results of complex processesprocesses

WhatWhat’’s perception for?s perception for?Evolutionary adaptionist viewEvolutionary adaptionist view

Shaped by environment to optimize fitnessShaped by environment to optimize fitnessAnimal perceptionAnimal perception

Olfactory sensitivity in dogsOlfactory sensitivity in dogs““smell facesmell face””

Bat Bat ““visionvision””Bird brains: Magnetic fieldsBird brains: Magnetic fields

What do they help us do?What do they help us do?Perceptual toolboxPerceptual toolboxWork with environmentWork with environmentWhat is perception for?What is perception for?

What's the problem to be solved?What's the problem to be solved?

What sense would you choose to lose?What sense would you choose to lose?

Sensation vs. PerceptionSensation vs. PerceptionSensation: workings of peripheral sensory Sensation: workings of peripheral sensory receptorsreceptors

Receptors are like little specialized Receptors are like little specialized ““peripheralsperipherals””Retina: Does your retina see?Retina: Does your retina see?

WhatWhat’’s frog vision like?s frog vision like?Hardwired? Hardwired?

Perception: working of the brain Perception: working of the brain The big CPU The big CPU Influence of knowledge, learningInfluence of knowledge, learningConsciousnessConsciousness

Sensation & PerceptionSensation & PerceptionItIt’’s not a clear distinctions not a clear distinction

The process of perceivingThe process of perceiving

The big question: Where/when does The big question: Where/when does ““perceptionperception”” start?start?

Start with the stimulus?Start with the stimulus?Not exactlyNot exactlyA tree falls in the forest A tree falls in the forest ……DonDon’’t see things behind t see things behind your head?your head?Must being looking at Must being looking at stimulusstimulus

““AttentionAttention””

ReceptorsReceptorsStimulus must fall on receptorsStimulus must fall on receptors

More restrictive for vision than hearing (< 180More restrictive for vision than hearing (< 180°°))What would vision be like if 360What would vision be like if 360°°??

E. AbottE. Abott’’s s ““flatlandsflatlands””

DonDon’’t t ““perceiveperceive”” whatwhat’’s on receptorss on receptorsE.g., inverted retinal imageE.g., inverted retinal image

DonDon’’t see world upside downt see world upside downPoke yourself in the eye!Poke yourself in the eye!

WhatWhat’’s up is downs up is downWhatWhat’’s right is lefts right is left

No need to No need to ““flipflip”” imageimageOr twist optic nerveOr twist optic nerve

The magic of sensory The magic of sensory transductiontransductionTransference of energy from one form Transference of energy from one form

to anotherto anotherPhysical/environmental energy to Physical/environmental energy to biological energybiological energyPhotosynthesis: Chemical energyPhotosynthesis: Chemical energy

Plants, bacteriaPlants, bacteriaSunlightSunlight——> sugar> sugar——>ATP (fuel)>ATP (fuel)

Sensory transduction: Electrical energySensory transduction: Electrical energyRetina: LightRetina: Light——>chemical>chemical——>electrical>electrical

Sensation: Process of transduction for Sensation: Process of transduction for different sensory systemsdifferent sensory systems

E.g., Touch: physical compression E.g., Touch: physical compression ——> > electrical energyelectrical energy

Neural processing INeural processing IWhere does it start?Where does it start?

ReceptorsReceptors——>Brain/neurons>Brain/neurons

Definition of periphery vs. Definition of periphery vs. brain brain

Brain is where signal Brain is where signal becomes electricalbecomes electrical

Retinal photoreceptors are Retinal photoreceptors are not part of the brainnot part of the brain

Neural processing IINeural processing IIIf you think the retina is complicated If you think the retina is complicated ……Hundreds of thousands Hundreds of thousands of receptors in retinaof receptors in retinaBillions of neuronsBillions of neuronsComplexity comes from Complexity comes from the connectionsthe connections

Each neurons has Each neurons has ~ 1000 connections ~ 1000 connections

Not random connectionsNot random connectionsControls flow of Controls flow of informationinformation

Neural processing IIINeural processing IIIWhat's the processing part?What's the processing part?Transformations and productsTransformations and products

MaltMalt——>Beer>Beerlightlight——>sight of beer>sight of beer

Perception IPerception ITransformation of electrical information into Transformation of electrical information into perceptual experienceperceptual experience

Depends on critical brain stages after receptor Depends on critical brain stages after receptor transduction transduction

Perception is conscious sensory experience? Perception is conscious sensory experience? Depends who you ask: Different research traditionsDepends who you ask: Different research traditionsCan you have perception without awareness?Can you have perception without awareness?

Subception (1940Subception (1940--50s)50s)processing of emotionally significant information processing of emotionally significant information unconsciouslyunconsciously

Perception II: Perception II: BottomBottom--up vs. Topup vs. Top--DownDown

Prof Anderson says: Prof Anderson says: ““This is where the cool stuff happensThis is where the cool stuff happens””

Can perception take place without knowledge of the world?Can perception take place without knowledge of the world?BottomBottom--upup

Information coming from receptors on upInformation coming from receptors on upTop downTop down

Brain is not Brain is not ““Tabula rasaTabula rasa””What effect does knowledge play in guiding the perceptual procesWhat effect does knowledge play in guiding the perceptual processsKnowledge is Knowledge is ““higherhigher--orderorder””, receptors , receptors ““lowerlower--orderorder””

Computer visionComputer visionGoal: perception based entirely on bottom up analysisGoal: perception based entirely on bottom up analysis

Knowledge dependence of Knowledge dependence of perceptual processingperceptual processing

Is knowledge needed toIs knowledge needed toderive cup shape?derive cup shape?

Or can object be Or can object be ““drawndrawn””in minds eye without in minds eye without knowledge?knowledge?

E.g. Gestalt groupingE.g. Gestalt groupingGood continuation Good continuation

Computers find task very Computers find task very difficultdifficult

Perception is much more than Perception is much more than the stimulusthe stimulus

ItIt’’s a constructive creative processs a constructive creative process

T E PE TE MY T PE

Recognition IRecognition IPerceptionPerception’’s contact with meanings contact with meaningCan we dissociate perception and Can we dissociate perception and recognition?recognition?

Yes and noYes and noBrain damage: Visual agnosiaBrain damage: Visual agnosia

Vision w/out knowledgeVision w/out knowledge

Can you perceive without Can you perceive without accessing knowledge?accessing knowledge?

ModularityModularityCertain bottomCertain bottom--up perceptual up perceptual processes are not influenced processes are not influenced by knowledgeby knowledge

Cognitive impenetrabilityCognitive impenetrabilityVisual illusions still occur Visual illusions still occur despite knowing they are despite knowing they are illusionsillusions

A mind is a terrible A mind is a terrible thing to waste (and taste)thing to waste (and taste)

Its almost impossible to not use your Its almost impossible to not use your knowledgeknowledgeCanCan’’t ask you to not recognize a wordt ask you to not recognize a word

Just process color, orientation of linesJust process color, orientation of linesKnowledge irrevocably changes the Knowledge irrevocably changes the process of perceptionprocess of perception

T E PE TE MY T PE

Where do top down Where do top down influences on perception influences on perception

start?start?Does knowledge (cognition), desire (emotion) Does knowledge (cognition), desire (emotion) influence how your retina works?influence how your retina works?

If youIf you’’re hungry does your retina start looking for re hungry does your retina start looking for steak? If you mentally imagine a steak does it steak? If you mentally imagine a steak does it appear on your retina? appear on your retina?

Unlikely. Rather, occurs at some later (higher) Unlikely. Rather, occurs at some later (higher) stage in your brainstage in your brain

Recognition II Recognition II Can we have recognition Can we have recognition without perception?without perception?

Access knowledge without Access knowledge without perceptual awareness?perceptual awareness?

YesYese.g., Amygdala unconscious e.g., Amygdala unconscious recognition of aversive stimuli recognition of aversive stimuli (associated with shock)(associated with shock)Unconscious semantic primingUnconscious semantic priming

Part 2: From brain to Part 2: From brain to perception and back againperception and back again

Levels of analysisLevels of analysisStudy experience (psychology)Study experience (psychology)Study brain (neuroscience)Study brain (neuroscience)Study relation between mind and brainStudy relation between mind and brain

Psychophysical analysis (Fechner, 1860s)Psychophysical analysis (Fechner, 1860s)Phenomenology (quality of experience, W. Wundt)Phenomenology (quality of experience, W. Wundt)

Wundt focused on qualitative studiesWundt focused on qualitative studiesQuantify relation between Quantify relation between ““objectiveobjective”” stimulus energy stimulus energy (physics) and (physics) and ““subjectivesubjective”” experience (psycho)experience (psycho)

Physiological analysis (nonhuman animals)Physiological analysis (nonhuman animals)How does electrical activity in brain relate to presented How does electrical activity in brain relate to presented stimulistimuliDifficult to assess experienceDifficult to assess experience

Human functional Human functional neuroimagingneuroimaging

Can assess the relation between stimulus, Can assess the relation between stimulus, neural response, and experience neural response, and experience conjointlyconjointly

What's the relation between What's the relation between mind and brain mind and brain

Brain ultimately determines perceptionBrain ultimately determines perceptionCan look to the brain for physiological Can look to the brain for physiological characteristics to tell us how perception workscharacteristics to tell us how perception worksCan also look to perception for how brain is Can also look to perception for how brain is organizedorganized

E.g., weird illusionsE.g., weird illusions

Silly human tricks: Silly human tricks: Psychophysical methods IPsychophysical methods I

Relation between stimulus and resulting Relation between stimulus and resulting perceptionperceptionThe Phenomenological methodThe Phenomenological method

Typically illusionsTypically illusionsDetectionDetection

Its all about thresholdsIts all about thresholdsVisual, auditory, touch, etcVisual, auditory, touch, etc

Types of methodsTypes of methodsLimits (up/down staircases)Limits (up/down staircases)Adjustment (volume knob)Adjustment (volume knob)Constant stimuli (find amount of energy where 50% correct Constant stimuli (find amount of energy where 50% correct detection)

Arcane fact # 1

detection)

Silly human tricks: Silly human tricks: Psychophysical methods IIPsychophysical methods IIDifference thresholds (Weber)Difference thresholds (Weber)

Smallest detectable difference Smallest detectable difference between two stimuli between two stimuli The Weber fractionThe Weber fraction

Amount of weight increases but proportion Amount of weight increases but proportion stays constantstays constant= Difference/standard= Difference/standard

This applies to most sensesThis applies to most sensesThink of it like the discovery of the Think of it like the discovery of the gravitational constant but applied to gravitational constant but applied to mental activity

5/100=.05

10/200=.05

mental activity

Signal Detection TheorySignal Detection TheoryProblems with sensory Problems with sensory thresholdsthresholds

““I hear/see itI hear/see it”” 50% of the 50% of the timetimeRepresents true sensory Represents true sensory threshold?threshold?

Classical psychophysical Classical psychophysical methodsmethods

No stimulus no response No stimulus no response (wrong)(wrong)Sensory system Sensory system vsvs observerobserver

Liberal Liberal vsvs conservative conservative criteria

100

Per

cent

“yes

”res

pons

e

Liberal

Conserv

Low0 High

Tone Intensitycriteria

Signal detection experimentSignal detection experimentTrials with and Trials with and withoutwithout a stimulus (e.g., a stimulus (e.g., Tone)Tone)

How often respond to stimulus? How often respond to stimulus? Hits (H)Hits (H)How often respond to no stimulus? How often respond to no stimulus? False False alarms (FA)alarms (FA)

Vito is liberalVito is liberal90% 90% HH, 40% , 40% FAFA, 90 , 90 -- 40 = 50%40 = 50%

Mario is conservativeMario is conservative60% 60% HH, 10% , 10% FAFA, 60 , 60 -- 10 = 50%10 = 50%

Equal discriminationEqual discrimination

Receiver operating Receiver operating characteriticscharacteritics (ROC)(ROC)

Plot H Plot H vsvs FAFA

Sensitivity increases Sensitivity increases with deviation from with deviation from diagonaldiagonal

Observers falling on Observers falling on curve have equal curve have equal threshold/sensitivity threshold/sensitivity

Liberal

Cons

Beyond thresholdsBeyond thresholdsMagnitude estimationMagnitude estimation

““I love you this muchI love you this much””I love my mom 2.46 times I love my mom 2.46 times as much as chocolateas much as chocolate

Give standard (say 10)Give standard (say 10)Judge other stimuli Judge other stimuli relative to standardrelative to standardStevensStevens’’s power laws power law

Compression vs. Compression vs. expansionexpansionPower functionsPower functionsPerceived Perceived magnitude=constant x magnitude=constant x stimulus intensitystimulus intensitynn

Part 3: Neurons and Part 3: Neurons and perceptionperception

The Neuron DoctrineThe Neuron DoctrineBrain Brain

Unicellular (common cytoplasm)Unicellular (common cytoplasm)vs. Multicellularvs. MulticellularNeuron as basis for mindNeuron as basis for mind

Neurons are specialNeurons are specialin brain, not other organsin brain, not other organs

Have special qualities that allow Have special qualities that allow for perceptionfor perception

Your liver or kidneys do not have Your liver or kidneys do not have the capacity for perceptionthe capacity for perceptionAristotle: Heart was the origin of Aristotle: Heart was the origin of mind and soulmind and soul

Neurons and perceptionNeurons and perceptionCutaneous receptor neuronCutaneous receptor neuron

Collection of sensory axons: Collection of sensory axons: Nerve bundleNerve bundleAxons from the the periphery Axons from the the periphery (receptors) are called nerves(receptors) are called nerves

Dendrites

Basic properties of neuronsBasic properties of neuronsWhat are the fundamental units What are the fundamental units of the neural code?of the neural code?

Action potentials (AP)Action potentials (AP)WhatWhat’’s the neural code? s the neural code?

How do neurons represent How do neurons represent stimulus intensity?stimulus intensity?Neurons Neurons ““firefire”” more APs more APs Do not fire larger APsDo not fire larger APsAnalog to digitalAnalog to digital

Excitation: Increases # of APsExcitation: Increases # of APsInhibition: Decreases # of APsInhibition: Decreases # of APs

Localization of brain functionLocalization of brain functionPerception is not created by a single neuronPerception is not created by a single neuronItIt’’s a result of many neuronss a result of many neurons

Antilocalizationists (Holists)Antilocalizationists (Holists)One brain systemOne brain systemOne faculty (sensation, memory, emotion)One faculty (sensation, memory, emotion)

LocalizationistsLocalizationistsMultiple brain systemsMultiple brain systemsMultiple facultiesMultiple faculties

Sensation, memory, emotion separateSensation, memory, emotion separate

PhrenologyPhrenologyFranz Gall (Early 1800s)Franz Gall (Early 1800s)Like palm readingLike palm reading~35 specific functions~35 specific functions

1 vs many faculties1 vs many facultiesMuscle metaphorMuscle metaphor

Bump on skullBump on skullRight and wrongRight and wrong

Localization of functionLocalization of function

Localization of perception:Localization of perception:Law of specific nerve Law of specific nerve

energiesenergiesMueller (early 1800s)Mueller (early 1800s)Specific perceptual quality (hearing, touch, Specific perceptual quality (hearing, touch, sight, taste, smell) depends on stimulation sight, taste, smell) depends on stimulation of specific nerves (of specific nerves (““nerve energiesnerve energies””))Critically depends on where in brain Critically depends on where in brain nerves connect tonerves connect to

Intracranial stimulation: Intracranial stimulation: Perception Perception

Epilepsy patientsEpilepsy patientsCan activate sensations of smell, sight, touch, hearing, Can activate sensations of smell, sight, touch, hearing, by stimulating the brain regions directly by stimulating the brain regions directly Perception happens in brain, not receptorsPerception happens in brain, not receptors

exposed cortex of exposed cortex of epilepsy patientepilepsy patient

grid work of electrodes grid work of electrodes laid over the surface for laid over the surface for stimulation and stimulation and recordingrecording

Specific perceptual qualities Specific perceptual qualities reside in distinct brain reside in distinct brain

regionsregionsThe primary cortical sensory regionsThe primary cortical sensory regions

Taste

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