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Psy280: PerceptionPsy280: Perception

Prof. AndersonProf. AndersonDepartment of PsychologyDepartment of Psychology

Vision 7Vision 7MotionMotion

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Optional papers: QuALMRIOptional papers: QuALMRI

nn QuQuestion/hypothesisestion/hypothesisnn AAlternativelternativenn LLogicogicnn MMethodethodnn RResultsesultsnn IInferencesnferences

nn Detailed description on websiteDetailed description on website

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Motion: Frames of referenceMotion: Frames of referencenn What does the term "at rest" mean?What does the term "at rest" mean?nn Can you cite an example of an object at rest?Can you cite an example of an object at rest?

nn Is the room at rest?Is the room at rest?nn Room has at least three types of motionRoom has at least three types of motion

nn Motion due to earth :Motion due to earth :24000 miles / 24 hours = 24000 miles / 24 hours = 10001000 miles/hr miles/hr

nn Earth circles the sun:Earth circles the sun:2 pi 93,000,000 miles / 8760 hours = 2 pi 93,000,000 miles / 8760 hours = 6670066700 miles/hr miles/hr

nn Sun circles the galaxy (30,000 light year = r) every 1 / 4Sun circles the galaxy (30,000 light year = r) every 1 / 4billion yearsbillion years1.76 x 101.76 x 101717 miles / 2.19 x 10 miles / 2.19 x 101212 hr = hr = 8040080400 miles/ hr miles/ hr

nn Is there anything that is not moving?Is there anything that is not moving?nn Must be careful about our description of motionMust be careful about our description of motionnn Moving relative to what reference frame?Moving relative to what reference frame?

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Animism: Worshiping the lightAnimism: Worshiping the lightnn Divides livingDivides living

organismsorganismsnn Animals vs plantsAnimals vs plantsnn Capacity forCapacity for

voluntary movementvoluntary movementnn vs phototropismvs phototropism

nn Co-evolutionCo-evolutionnn Organisms that moveOrganisms that movenn Evolution of aEvolution of a

capacity to sensecapacity to sensemovementmovement

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Invisible motion:Invisible motion:Morning gloryMorning glory

nn 5 AM to 7PM5 AM to 7PMnn Open in morningOpen in morning

nn Pollination by diurnalPollination by diurnalinsectinsect

nn Dies in afternoonDies in afternoonnn Motion too slow toMotion too slow to

notice even dramaticnotice even dramaticchangechange

nn Our visual system areOur visual system aretuned to events thattuned to events thatmove more quicklymove more quicklynn E.g., Animals (fast) notE.g., Animals (fast) not

plants (slow)plants (slow)

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Motion and change detectionMotion and change detection

nn Visual motion is sensing change in retinalVisual motion is sensing change in retinalimage (sort of)image (sort of)

nn As duration between changes increasesAs duration between changes increasesperception of motion decreasesperception of motion decreases

nn Motion is a perceptual adaptation forMotion is a perceptual adaptation fordetection of change, otherwise invisible todetection of change, otherwise invisible tothe eyethe eye

Can’t telldifference acrossspace

Can tell difference across time

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Motion and the retinal imageMotion and the retinal image

nn Change in image intensity (luminance)Change in image intensity (luminance)over timeover timenn Dark to lightDark to lightnn Light to darkLight to dark

Difference image

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Illusory movement:Illusory movement:Apparent motionApparent motion

nn Luminance changeLuminance changenn No physical continuityNo physical continuitynn Infer motion whereInfer motion where

none is presentnone is presentnn CriticalCritical

temporal/spatialtemporal/spatialparametersparametersnn Simultaneous flickerSimultaneous flicker

nn <10 ms interval<10 ms intervalnn Perceive 2 eventsPerceive 2 events

nn MotionMotionnn ~60 ms interval~60 ms intervalnn Perceive 1 eventPerceive 1 event

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Not just simple luminance change:Not just simple luminance change:2nd order motion2nd order motion

nn First-order motionFirst-order motionnn Change in luminanceChange in luminance

boundaryboundarynn Luminance changeLuminance change

doesndoesn’’t explain allt explain allmotionmotion

nn Second-order motionSecond-order motionnn Motion but noMotion but no

luminance boundaryluminance boundarynn Not net luminanceNot net luminance

changechangenn Object disappearsObject disappears

when motion stopswhen motion stops

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Second order motion:Second order motion:Illusory shapes and motionIllusory shapes and motion

nn No luminanceNo luminanceboundary for low-levelboundary for low-levelmotion detectors to usemotion detectors to use

nn Motion perceptionMotion perceptionmust rely on other top-must rely on other top-down/higher-orderdown/higher-orderinfluencesinfluences

nn Simple luminanceSimple luminancebased motion detectorsbased motion detectorscancan’’t explain all oft explain all ofmotion perceptionmotion perception

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Simple luminance detectors wonSimple luminance detectors won’’t do:t do:The aperture problemThe aperture problem

nn Narrow view of world through small receptiveNarrow view of world through small receptivefields (RF)fields (RF)nn Ambiguity of direction of motionAmbiguity of direction of motion

nn Need additional info for accurate motionNeed additional info for accurate motionsensingsensingnn Edges or textureEdges or texture

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The aperture problemThe aperture problemnn Looking at motionLooking at motion

through the windowthrough the windowof one neuronof one neuron

nn RF representsRF representshorizontal motionhorizontal motion

nn Global scene hasGlobal scene hasdifferent motiondifferent motionnn Local computationsLocal computations

dondon’’t necessarilyt necessarilyexplain motionexplain motion

nn Need to shareNeed to shareinformation acrossinformation acrossneuronsneurons

Perceived motion

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Motion perception:Motion perception:More than the sum of its partsMore than the sum of its partsn The underlying mechanism involves

signals at different retinal locations beingintegrated to arrive at global motionsignals

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Motion integration at the sameMotion integration at the sameretinal location: Plaidsretinal location: Plaids

nn First order low-levelFirst order low-levelmotion detectorsmotion detectorsnn Respond to eachRespond to each

component of motioncomponent of motion(horizontal and(horizontal andvertical)vertical)

nn Motion integrationMotion integrationnn DonDon’’t perceive eithert perceive eithernn Create commonCreate common

directional signaldirectional signalnn Like force vectorsLike force vectors

nn Down & left movingDown & left movingplaidplaid

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Motion detection as anMotion detection as anopponent processopponent process

nn LikeLike colour colour vision: Red-green, blue-yellowvision: Red-green, blue-yellow

nn MotionMotionnn Up-downUp-downnn Left-rightLeft-rightnn Spiral in-outSpiral in-out

nn Enhances Enhances ““motion contrastmotion contrast””

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Motion after effectMotion after effectnn Reversing waterfallReversing waterfallnn Fatigue your directionFatigue your direction

sensitive neuronssensitive neuronsnn See opposite motionSee opposite motion

where there is nonewhere there is nonenn ExplanationExplanation

nn No motionNo motionnn Direction selective cellsDirection selective cells

produce equal responsesproduce equal responsesnn No longer equally opposeNo longer equally oppose

each othereach othernn E.g., Adapt toE.g., Adapt to

redred——>perceive green>perceive green

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Spiral motion after effect:Spiral motion after effect:Disfiguring BradDisfiguring Brad

• Fatigue neurons representing radial expansion• Induces radial contraction due to lessened inhibitory influence• Motion (perception) is a perceptual/neural process, not necessarilya property of the world (object movement)!

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Direction repulsion: LateralDirection repulsion: Lateralinhibitory influences in motioninhibitory influences in motionnn Vertical and 45Vertical and 45

degree movementdegree movementnn Interact to enlargeInteract to enlarge

directional disparitydirectional disparitynn Evidence of lateralEvidence of lateral

inhibitory interactionsinhibitory interactionsbetween motionbetween motiondetectorsdetectors

nn Enhancement ofEnhancement ofdirectional directional ““contrastcontrast””

nn Motion Motion ““mach bandsmach bands””

Actual Perceived

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Perceptual organization:Perceptual organization:Structure from motionStructure from motion

nn Motion perception notMotion perception notused just to assessused just to assessstimulus movementstimulus movement

nn Can define Can define ““objectsobjects””nn Laws of organizationLaws of organization

nn Common fateCommon fatenn Things that moveThings that move

together belong to sametogether belong to sameobjectobject

nn A camouflaged animalA camouflaged animalis difficult to see until itis difficult to see until itmovesmoves

nn Not just knowledgeNot just knowledgebasedbasednn Can see novel objectsCan see novel objects

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Structure from motion:Structure from motion:Kinetic depthKinetic depth

nn Can define depthCan define depthnn What motion cuesWhat motion cues

define depth?define depth?nn ParallaxParallax

nn Differing dot velocityDiffering dot velocitynn Track single dotTrack single dot

nn See velocity changeSee velocity change

nn Infer depth fromInfer depth frommotionmotion

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Kinetic depth: Shadow motionKinetic depth: Shadow motionnn Moving shadows areMoving shadows are

also strong cue foralso strong cue fordepth changedepth change

nn HeuristicHeuristicnn Ambiguous infoAmbiguous info

nn Shadow might reflectShadow might reflectlight source movementlight source movement

nn Assume light source isAssume light source isconstantconstant

nn Sun doesnSun doesn’’t move thatt move thatfastfast

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Experience and motionExperience and motionperception: Biological motionperception: Biological motionnn Dot walkersDot walkersnn We each have ourWe each have our

own motionown motionsignaturesignaturenn Recognition byRecognition by

motionmotionnn ExperienceExperience

influences motioninfluences motionperceptionperception

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Motion from structureMotion from structure

nn Not only canNot only canmotion inducemotion induceshape perceptionshape perception

nn Shape can induceShape can inducemotion perceptionmotion perception

nn Top-downTop-downinfluencesinfluencesnn FFA/IT FFA/IT ——> MT> MT

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Motion from structureMotion from structure

nn Not only canNot only canmotion inducemotion induceshape perceptionshape perception

nn Shape can induceShape can inducemotion perceptionmotion perception

nn Top-downTop-downinfluencesinfluencesnn FFA/IT FFA/IT ——> MT> MT

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How does the brain representHow does the brain representmotion?motion?

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V1: Simple motion detectorsV1: Simple motion detectorsnn Directionally selectiveDirectionally selectivenn E.g., right ward and upE.g., right ward and up

nn Small receptive fieldsSmall receptive fieldsnn Local not global motionLocal not global motion

nn Thus, respond toThus, respond tocomponents of a plaid, notcomponents of a plaid, notperceived directionperceived direction

nn Higher level info mustHigher level info mustoverride V1 simple motionoverride V1 simple motion

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Designing a directionallyDesigning a directionallyselective V1 neuronselective V1 neuron

nn Temporal componentTemporal componentnn Built in delaysBuilt in delays

nn Neuron to neuronNeuron to neuroncommunication takescommunication takestimetime

nn Timing of inhibition isTiming of inhibition iscriticalcritical

nn Results in neuron likingResults in neuron likingright to left motionright to left motionnn Not left to rightNot left to right

Delayed inhibition

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The brainThe brain’’s motion eye:s motion eye:Area MT (V5)Area MT (V5)

nn Middle temporal area (MT)Middle temporal area (MT)nn Dorsal streamDorsal streamnn 90% of cells are directionally90% of cells are directionally

selectiveselectivenn Organized in directionalOrganized in directional

columnscolumnsnn Like V1 orientation or IT shapeLike V1 orientation or IT shape

columnscolumnsnn Stimulation of columnStimulation of column

increases directional motionincreases directional motionperceptionperception

nn 100 times larger than V1 RFs100 times larger than V1 RFsnn Wide view of worldWide view of worldnn Good for composite motionGood for composite motion

Human MT

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MT motion processing:MT motion processing:Random dot stimuliRandom dot stimuli

nn 0%, 30%, and 100% coherence0%, 30%, and 100% coherencenn Use to determine monkey/humanUse to determine monkey/human

detection of directional motiondetection of directional motion

nn How do we know MT supports motionHow do we know MT supports motionperception?perception?

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Psychophysical and neuralPsychophysical and neuralmotion response profilesmotion response profiles

nn NeuronsNeuronsresponse relate toresponse relate toperceptualperceptualexperience ofexperience ofmotion?motion?

nn MT neuron firingMT neuron firingrate parallelsrate parallelsperceptionperception

Neuron and observer motion detection

Random dots

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Stimulation of MT and motionStimulation of MT and motionnn Neurons responseNeurons response

correlatedcorrelated with withperceptualperceptualexperience ofexperience ofmotionmotion

nn Causally related?Causally related?nn Stimulation of MTStimulation of MT

increasesincreasespropensity topropensity toperceive motion inperceive motion incertain directioncertain direction

Right

Left

Proportion seen right directed motion

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After MT:After MT:Increasing complexity/specificityIncreasing complexity/specificitynn Medial superiorMedial superior

temporal (MST)temporal (MST)nn More specificMore specific

patternspatternsnn Expansion/Expansion/

contractioncontractionnn Superior temporalSuperior temporal

sulcus (STS)sulcus (STS)nn Biological motionBiological motion

nn HigherarchicalHigherarchicalorganization andorganization andsepcificity sepcificity codingcodingextends to motionextends to motion

Neuron 1 Neuron 2

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Keeping the world stillKeeping the world stillnn Given examples of motion w/out retinal changeGiven examples of motion w/out retinal change

nn E.g., motion after effectsE.g., motion after effectsnn What about retinal change w/out motion?What about retinal change w/out motion?nn Eyes constantly make small fast movementsEyes constantly make small fast movements

nn Remember: World fades without these movementsRemember: World fades without these movementsnn Why doesnWhy doesn’’t world appear to shake?t world appear to shake?

nn Would get pretty nauseatingWould get pretty nauseatingnn Vision needs to Vision needs to ““correctcorrect”” for eye movements for eye movementsnn How does it do it?How does it do it?

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Corollary discharge theoryCorollary discharge theorynn Integration of retinal stimulation and eyeIntegration of retinal stimulation and eye

movementsmovementsnn Use motor signals to stabilize visionUse motor signals to stabilize vision

nn Head movementHead movementnn Eye movementEye movement

nn How about movement without motorHow about movement without motorsignal?signal?nn (keep one eye closed) Push your open eye.(keep one eye closed) Push your open eye.

Gently please!Gently please!nn World moves!World moves!

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Corollary discharge theoryCorollary discharge theorynn 3 signals3 signals

nn Motor (MS)Motor (MS)nn Image movement (IMS)Image movement (IMS)nn Corollary discharge (CDS)Corollary discharge (CDS)

nn Comparator (c)Comparator (c)nn Eye (IMS) and motorEye (IMS) and motor

signals (MS) need to besignals (MS) need to becomparedcompared

nn CDS is a copy of motorCDS is a copy of motorsignalsignal

nn CDS and IMS cancel each CDS and IMS cancel eachotherother

nn When both are present noWhen both are present nosignal sent to visual cortexsignal sent to visual cortexnn ——> No perception of> No perception of

motionmotion

Visual cortex

CDS

Motor cortex

IMS

C

MS

Eye

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Corollary discharge theoryCorollary discharge theorynn Anytime CDS and IMS donAnytime CDS and IMS don’’t co-occur t co-occur ——>>

perceive motionperceive motionnn IMS alone IMS alone ——> perceive motion> perceive motion

nn Veridical movementVeridical movementnn Eyes still, stimulus movesEyes still, stimulus moves

nn Illusory movementIllusory movementnn Pushing your eyePushing your eyenn Move image on retinaMove image on retinaw/out MS/CDSw/out MS/CDS

nn This theory makes interesting predictionsThis theory makes interesting predictionsnn CDS alone should also result in motionCDS alone should also result in motion

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CDS: Moving after images!CDS: Moving after images!nn CDS without IMSCDS without IMS

nn DoesnDoesn’’t often happent often happennn No canceling of IMS andNo canceling of IMS and

CDSCDSnn Should result in motionShould result in motion

perceptionperceptionnn After imagesAfter images

nn No IMSNo IMSnn Fatigued photoreceptorsFatigued photoreceptors

result in stationaryresult in stationary““stimulusstimulus””

nn MS/CDS without IMSMS/CDS without IMSnn After images moveAfter images move

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CDS alone results in motionCDS alone results in motionperceptionperception

nn Track a flying birdTrack a flying birdnn No IMS, stabilized on retinaNo IMS, stabilized on retinann MS/CDS without IMSMS/CDS without IMSnn CDS activates motion perception in cortexCDS activates motion perception in cortex

nn Paralyze eye musclesParalyze eye musclesnn Can send MS but no eye movementCan send MS but no eye movement

nn MS/CDS without IMSMS/CDS without IMSnn Stationary events appear to moveStationary events appear to move

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““Real movementReal movement”” neurons neuronsnn Higher order corticalHigher order cortical

neurons (e.g. V3)neurons (e.g. V3)nn Bar moves through RFBar moves through RF

nn Move barMove barnn Move eyesMove eyes

nn Retinal stimulation heldRetinal stimulation heldconstantconstant

nn Respond most when notRespond most when notmoving eyesmoving eyes

Real movement neuron

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The EndThe End