Psy 280: Psy 280: PerceptionPerception

Prof. AndersonProf. Anderson

Department of PsychologyDepartment of Psychology

Week 2Week 2

Part 1: Part 1: The process of The process of

perceptionperception

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

Light reactive chemicalLight reactive chemical 2 fleshy antennae on side of 2 fleshy antennae on side of

headhead Pressure sensitive hairsPressure sensitive hairs

Cutaneous membraneCutaneous membrane Little detectors of different shapesLittle detectors of different shapes

Temperature, pain, caressTemperature, pain, caress

Bilateral air holesBilateral air holes Chemical sampling of gasesChemical sampling of gases

Retractable probeRetractable probe Chemical sampling of solids, Chemical sampling of solids,

liquids liquids

Perception is easyPerception is easy MisleadingMisleading World is projected on retina —> “vision”World is projected on retina —> “vision”

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

Computer visionComputer vision MIT student summer projectMIT student summer project

No privileged access to No privileged access to how perception workshow perception works

Perception is not just about Perception is not just about introspectionintrospection

Can’t introspect about working of Can’t introspect about working of the brain directlythe brain directly

Have access to the results of Have access to the results of complex processescomplex processes

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

Shaped by environment to optimize fitnessShaped by environment to optimize fitness Animal perceptionAnimal perception

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

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

What do they help us do?What do they help us do? Perceptual toolboxPerceptual toolbox Work with environmentWork with environment What 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. Perception Sensation: workings of peripheral sensory Sensation: workings of peripheral sensory

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

What’s frog vision like?What’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, learning ConsciousnessConsciousness

Sensation & PerceptionSensation & Perception It’s not a clear distinctionIt’s not a clear distinction

The process of perceivingThe process of perceiving

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

Start with the stimulus?Start with the stimulus? Not exactlyNot exactly A tree falls in the forest …A tree falls in the forest … Don’t see things behind your Don’t see things behind your

head?head? Must being looking at Must being looking at

stimulusstimulus ““Attention”Attention”

ReceptorsReceptors Stimulus must fall on receptorsStimulus must fall on receptors

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

E. Abott’s “flatlands”E. Abott’s “flatlands”

Don’t “perceive” what’s on receptorsDon’t “perceive” what’s on receptors E.g., inverted retinal imageE.g., inverted retinal image

Don’t see world upside downDon’t see world upside down Poke yourself in the eye!Poke yourself in the eye!

What’s up is downWhat’s up is down What’s right is leftWhat’s right is left

No need to “flip” imageNo need to “flip” image Or twist optic nerveOr twist optic nerve

The magic of sensory The magic of sensory transductiontransduction Transference of energy from one form to Transference of energy from one form to

anotheranother Physical/environmental energy to Physical/environmental energy to

biological energybiological energy Photosynthesis: Chemical energyPhotosynthesis: Chemical energy

Plants, bacteriaPlants, bacteria Sunlight—> sugar—>ATP (fuel)Sunlight—> sugar—>ATP (fuel)

Sensory transduction: Electrical energySensory transduction: Electrical energy Retina: Light—>chemical—>electricalRetina: Light—>chemical—>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 I Where does it start?Where does it start?

Receptors—>Brain/Receptors—>Brain/neuronsneurons

Definition of periphery Definition of periphery vs. brain vs. brain Brain is where signal Brain is where signal

becomes electricalbecomes electrical

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

Neural processing IINeural processing II If 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 retina

Billions of neuronsBillions of neurons Complexity comes Complexity comes

from the connectionsfrom the connections Each neurons has Each neurons has

~ 1000 connections ~ 1000 connections Not random connectionsNot random connections Controls flow of Controls flow of

informationinformation

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

Malt—>BeerMalt—>Beer light—>sight of beerlight—>sight of beer

Perception IPerception I Transformation 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 Depends who you ask: Different research traditionstraditions

Can you have perception without awareness?Can you have perception without awareness? Subception (1940-50s)Subception (1940-50s)

processing of emotionally significant information processing of emotionally significant information unconsciouslyunconsciously

Perception II: Perception II: Bottom-up vs. Top-DownBottom-up vs. Top-Down

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

Can perception take place without knowledge of the Can perception take place without knowledge of the world?world?

Bottom-upBottom-up Information coming from receptors on upInformation coming from receptors on up

Top downTop down Brain is not “Tabula rasa”Brain is not “Tabula rasa” What effect does knowledge play in guiding the perceptual What effect does knowledge play in guiding the perceptual

processprocess Knowledge is “higher-order”, receptors “lower-order”Knowledge is “higher-order”, receptors “lower-order”

Computer visionComputer vision Goal: perception based entirely on bottom up analysisGoal: perception based entirely on bottom up analysis

Knowledge dependence Knowledge dependence of perceptual processingof perceptual processing

Is knowledge needed Is knowledge needed toto

derive cup shape?derive cup shape? Or can object be Or can object be

“drawn” in minds eye “drawn” in minds eye without knowledge?without knowledge? E.g. Gestalt groupingE.g. Gestalt grouping

Good continuation Good continuation Computers find task Computers find task

very difficultvery difficult

Perception is much more Perception is much more than the stimulusthan the stimulus

T E PE TE MY T PE

It’s a constructive creative processIt’s a constructive creative process

Recognition IRecognition I Perception’s contact with meaningPerception’s contact with meaning Can we dissociate perception and Can we dissociate perception and

recognition?recognition? Yes and noYes and no Brain 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?

ModularityModularity Certain bottom-up Certain bottom-up

perceptual processes are perceptual processes are not influenced by not influenced by knowledgeknowledge

Cognitive impenetrabilityCognitive impenetrability Visual 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 thing to waste (and

taste)taste) Its almost impossible to not use your Its almost impossible to not use your

knowledgeknowledge Can’t ask you to not recognize a Can’t ask you to not recognize a

wordword Just process color, orientation of linesJust process color, orientation of lines

Knowledge 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 Does knowledge (cognition), desire

(emotion) influence how your retina works?(emotion) influence how your retina works?

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

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

e.g., Amygdala unconscious e.g., Amygdala unconscious recognition of aversive recognition of aversive stimuli (associated with stimuli (associated with shock)shock)

Unconscious semantic Unconscious semantic primingpriming

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

againagain Levels of analysisLevels of analysis Study 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 studies Quantify relation between “objective” stimulus energy Quantify relation between “objective” stimulus energy

(physics) and “subjective” experience (psycho)(physics) and “subjective” 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 stimulistimuli

Difficult to assess experienceDifficult to assess experience

Human functional Human functional neuroimagingneuroimaging

Can assess the relation between Can assess the relation between stimulus, neural response, and stimulus, neural response, and experience conjointlyexperience conjointly

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

Brain ultimately determines perceptionBrain ultimately determines perception Can look to the brain for physiological Can look to the brain for physiological

characteristics to tell us how perception characteristics to tell us how perception worksworks

Can also look to perception for how brain Can also look to perception for how brain is organizedis organized E.g., weird illusionsE.g., weird illusions

Silly human tricks: Silly human tricks: Psychophysical methods Psychophysical methods

II Relation between stimulus and resulting Relation between stimulus and resulting perceptionperception

The Phenomenological methodThe Phenomenological method Typically illusionsTypically illusions

DetectionDetection Its all about thresholdsIts all about thresholds

Visual, auditory, touch, etcVisual, auditory, touch, etc Types of methodsTypes of methods

Limits (up/down staircases)Limits (up/down staircases) Adjustment (volume knob)Adjustment (volume knob) Constant stimuli (find amount of energy where 50% Constant stimuli (find amount of energy where 50%

correct detection)correct detection)

Arcane fact # 1

Silly human tricks: Silly human tricks: Psychophysical methods Psychophysical methods

IIII Difference 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 Amount of weight increases but proportion stays constantproportion stays constant

= Difference/standard= Difference/standard This applies to most sensesThis applies to most senses Think of it like the discovery of Think of it like the discovery of

the gravitational constant but the gravitational constant but applied to mental activityapplied to mental activity

5/100=.05

10/200=.05

Signal Detection TheorySignal Detection Theory Problems with sensory Problems with sensory

thresholdsthresholds ““I hear/see it” 50% of the I hear/see it” 50% of the

timetime Represents true sensory Represents true sensory

threshold?threshold? Classical psychophysical Classical psychophysical

methodsmethods No stimulus no response No stimulus no response

(wrong)(wrong) Sensory system vs observerSensory system vs observer

Liberal vs conservative Liberal vs conservative criteriacriteria

Tone Intensity

Per

cent

“ye

s” r

espo

nse

Liberal

Conserv

Low High0

100

Signal detection Signal detection experimentexperiment

Trials with and Trials with and withoutwithout a stimulus a stimulus (e.g., Tone)(e.g., 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 alarms (FA)False alarms (FA) Vito is liberalVito is liberal

90% 90% HH, 40% , 40% FAFA, 90 - 40 = 50%, 90 - 40 = 50% Mario is conservativeMario is conservative

60% 60% HH, 10% , 10% FAFA, 60 - 10 = 50%, 60 - 10 = 50% Equal discriminationEqual discrimination

Receiver operating Receiver operating characteritics (ROC)characteritics (ROC)

Plot H vs FAPlot H vs FA

Sensitivity Sensitivity increases with increases with deviation from deviation from diagonaldiagonal

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

Liberal

Cons

Beyond thresholdsBeyond thresholds Magnitude estimationMagnitude estimation

““I love you this much”I 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 standard Stevens’s power lawStevens’s power law

Compression vs. expansionCompression vs. expansion Power functionsPower functions Perceived Perceived

magnitude=constant x magnitude=constant x stimulus intensitystimulus intensitynn

Part 3: Neurons and Part 3: Neurons and perceptionperception

The Neuron DoctrineThe Neuron Doctrine Brain Brain

Unicellular (common Unicellular (common cytoplasm)cytoplasm)

vs. Multicellularvs. Multicellular Neuron as basis for mindNeuron as basis for mind

Neurons are specialNeurons are special in brain, not other organsin brain, not other organs

Have special qualities that Have special qualities that allow for perceptionallow for perception

Your liver or kidneys do not have Your liver or kidneys do not have the capacity for perceptionthe capacity for perception

Aristotle: Heart was the origin of Aristotle: Heart was the origin of mind and soulmind and soul

Neurons and perceptionNeurons and perception Cutaneous receptor neuronCutaneous receptor neuron

Collection of sensory axons: Collection of sensory axons: Nerve bundleNerve bundle

Axons from the the periphery Axons from the the periphery (receptors) are called nerves(receptors) are called nerves

Dendrites

Basic properties of Basic properties of neuronsneurons

What are the fundamental What are the fundamental units of the neural code?units of the neural code? Action potentials (AP)Action potentials (AP)

What’s the neural code? What’s the neural code? How do neurons represent How do neurons represent

stimulus intensity?stimulus intensity? Neurons “fire” more APs Neurons “fire” more APs Do not fire larger APsDo not fire larger APs Analog to digitalAnalog to digital

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

APsAPs

Localization of brain Localization of brain functionfunction

Perception is not created by a single neuronPerception is not created by a single neuron It’s a result of many neuronsIt’s a result of many neurons

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

LocalizationistsLocalizationists Multiple brain systemsMultiple brain systems Multiple facultiesMultiple faculties

Sensation, memory, emotion separateSensation, memory, emotion separate

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

1 vs many faculties1 vs many faculties Muscle metaphorMuscle metaphor

Bump on skullBump on skull Right and wrongRight and wrong

Localization of functionLocalization of function

Localization of Localization of perception:perception:

Law of specific nerve Law of specific nerve energiesenergies Mueller (early 1800s)Mueller (early 1800s)

Specific perceptual quality (hearing, Specific perceptual quality (hearing, touch, sight, taste, smell) depends touch, sight, taste, smell) depends on stimulation of specific nerves on stimulation of specific nerves (“nerve energies”)(“nerve energies”)

Critically depends on where in brain Critically depends on where in brain nerves connect tonerves connect to

Epilepsy patientsEpilepsy patients Can activate sensations of smell, sight, touch, Can activate sensations of smell, sight, touch,

hearing, by stimulating the brain regions directly hearing, by stimulating the brain regions directly Perception happens in brain, not receptorsPerception happens in brain, not receptors

exposed cortex of epilepsy exposed cortex of epilepsy patientpatient

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

Intracranial stimulation: Intracranial stimulation: Perception Perception

Specific perceptual Specific perceptual qualities reside in qualities reside in

distinct brain regionsdistinct brain regions The primary cortical sensory regionsThe primary cortical sensory regions

Taste

End of SectionEnd of Section