psy280: perception
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Psy280: Psy280: PerceptionPerception
Prof. AndersonProf. AndersonDepartment of PsychologyDepartment of Psychology
Vision 7Vision 7MotionMotion
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Optional papers: Optional papers: QuALMRIQuALMRI
QuQuestion/hypothesisestion/hypothesis AAlternativelternative LLogicogic MMethodethod RResultsesults IInferencesnferences
Detailed description on websiteDetailed description on website
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Motion: Frames of Motion: Frames of referencereference
What does the term "at rest" mean?What does the term "at rest" mean? Can you cite an example of an object at rest?Can you cite an example of an object at rest?
Is the room at rest? Is the room at rest? Room has at least three types of motion Room has at least three types of motion
Motion due to earth :Motion due to earth :24000 miles / 24 hours = 24000 miles / 24 hours = 10001000 miles/hr miles/hr
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
Sun circles the galaxy (30,000 light year = r) every 1 / 4 billion Sun circles the galaxy (30,000 light year = r) every 1 / 4 billion years years 1.76 x 101.76 x 101717 miles / 2.19 x 10 miles / 2.19 x 101212 hr = hr = 8040080400 miles/ hr miles/ hr
Is there anything that is not moving?Is there anything that is not moving? Must be careful about our description of motionMust be careful about our description of motion Moving relative to what reference frame?Moving relative to what reference frame?
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Animism: Worshiping the Animism: Worshiping the lightlight
Divides living Divides living organismsorganisms Animals vs plantsAnimals vs plants Capacity for Capacity for
voluntary movement voluntary movement vs phototropismvs phototropism
Co-evolutionCo-evolution Organisms that Organisms that
movemove Evolution of a Evolution of a
capacity to sense capacity to sense movementmovement
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Invisible motion: Invisible motion: Morning gloryMorning glory
5 AM to 7PM5 AM to 7PM Open in morningOpen in morning
Pollination by diurnal Pollination by diurnal insectinsect
Dies in afternoonDies in afternoon Motion too slow to Motion too slow to
notice even dramatic notice even dramatic changechange
Our visual system are Our visual system are tuned to events that tuned to events that move more quicklymove more quickly E.g., Animals (fast) not E.g., Animals (fast) not
plants (slow)plants (slow)
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Motion and change Motion and change detectiondetection
Visual motion is sensing change in Visual motion is sensing change in retinal image (sort of)retinal image (sort of)
As duration between changes As duration between changes increases perception of motion increases perception of motion decreasesdecreases
Motion is a perceptual adaptation Motion is a perceptual adaptation for detection of change, otherwise for detection of change, otherwise invisible to the eyeinvisible to the eyeCan’t tell
difference across space
Can tell difference across time
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Motion and the retinal Motion and the retinal imageimage
Change in image intensity Change in image intensity (luminance) over time(luminance) over time Dark to lightDark to light Light to darkLight to dark
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Illusory movement:Illusory movement:Apparent motionApparent motion
Luminance changeLuminance change No physical No physical
continuitycontinuity Infer motion where Infer motion where
none is presentnone is present Critical Critical
temporal/spatial temporal/spatial parametersparameters Simultaneous flicker Simultaneous flicker
<10 ms interval<10 ms interval Perceive 2 eventsPerceive 2 events
MotionMotion ~60 ms interval~60 ms interval Perceive 1 eventPerceive 1 event
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Not just simple luminance Not just simple luminance change: 2nd order motionchange: 2nd order motion First-order motionFirst-order motion
Change in luminance Change in luminance boundaryboundary
Luminance change Luminance change doesn’t explain all doesn’t explain all motionmotion
Second-order motionSecond-order motion Motion but no Motion but no
luminance boundaryluminance boundary Not net luminance Not net luminance
changechange Object disappears Object disappears
when motion stopswhen motion stops
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Second order motion:Second order motion:Illusory shapes and Illusory shapes and
motionmotion No luminance No luminance boundary for low-level boundary for low-level motion detectors to usemotion detectors to use
Motion perception Motion perception must rely on other top-must rely on other top-down/higher-order down/higher-order influencesinfluences
Simple luminance Simple luminance based motion detectors based motion detectors can’t explain all of can’t explain all of motion perceptionmotion perception
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Simple luminance detectors Simple luminance detectors won’t do: The aperture won’t do: The aperture
problemproblem Narrow view of world through small receptive Narrow view of world through small receptive
fields (RF)fields (RF) Ambiguity of direction of motionAmbiguity of direction of motion
Need additional info for accurate motion sensingNeed additional info for accurate motion sensing Edges or textureEdges or texture
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The aperture problemThe aperture problem Looking at motion Looking at motion
through the through the window of one window of one neuronneuron
RF represents RF represents horizontal motionhorizontal motion
Global scene has Global scene has different motiondifferent motion Local computations Local computations
don’t necessarily don’t necessarily explain motionexplain motion
Need to share Need to share information across information across neuronsneurons Perceived motion
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Motion perception: Motion perception: More than the sum of its More than the sum of its
partsparts The underlying mechanism involves
signals at different retinal locations being integrated to arrive at global motion signals
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Motion integration at the Motion integration at the same retinal location: same retinal location:
PlaidsPlaids First order low-level First order low-level motion detectors motion detectors Respond to each Respond to each
component of motion component of motion (horizontal and vertical)(horizontal and vertical)
Motion integrationMotion integration Don’t perceive eitherDon’t perceive either Create common Create common
directional signaldirectional signal Like force vectorsLike force vectors
Down & left moving Down & left moving plaidplaid
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Motion detection as an Motion detection as an opponent processopponent process
Like colour vision: Red-green, blue-Like colour vision: Red-green, blue-yellowyellow
MotionMotion Up-downUp-down Left-rightLeft-right Spiral in-out Spiral in-out
Enhances “motion contrast”Enhances “motion contrast”
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Motion after effectMotion after effect Reversing waterfallReversing waterfall Fatigue your direction Fatigue your direction
sensitive neuronssensitive neurons See opposite motion See opposite motion
where there is nonewhere there is none ExplanationExplanation
No motionNo motion Direction selective cells Direction selective cells
produce equal responsesproduce equal responses No longer equally oppose No longer equally oppose
each othereach other E.g., Adapt to red—E.g., Adapt to red—
>perceive green>perceive green
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Spiral motion after Spiral motion after effect: Disfiguring Bradeffect: Disfiguring Brad
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• Fatigue neurons representing radial expansion• Induces radial contraction due to lessened inhibitory influence• Motion (perception) is a perceptual/neural process, not necessarily a property of the world (object movement)!
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Direction repulsion: Direction repulsion: Lateral inhibitory Lateral inhibitory
influences in motioninfluences in motion Vertical and 45 Vertical and 45
degree movementdegree movement Interact to enlarge Interact to enlarge
directional disparitydirectional disparity Evidence of lateral Evidence of lateral
inhibitory inhibitory interactions between interactions between motion detectorsmotion detectors
Enhancement of Enhancement of directional “contrast”directional “contrast”
Motion “mach bands”Motion “mach bands”
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Actual Perceived
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Perceptual organization: Perceptual organization: Structure from motionStructure from motion
Motion perception Motion perception not used just to assess not used just to assess stimulus movementstimulus movement
Can define “objects”Can define “objects” Laws of organizationLaws of organization
Common fateCommon fate Things that move Things that move
together belong to together belong to same objectsame object
A camouflaged animal A camouflaged animal is difficult to see until is difficult to see until it movesit moves
Not just knowledge Not just knowledge basedbased Can see novel objectsCan see novel objects
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Structure from motion: Structure from motion: Kinetic depthKinetic depth
Can define depthCan define depth What motion cues What motion cues
define depth?define depth? ParallaxParallax
Differing dot Differing dot velocityvelocity
Track single dotTrack single dot See velocity changeSee velocity change
Infer depth from Infer depth from motionmotion
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Kinetic depth: Shadow Kinetic depth: Shadow motionmotion
Moving shadows are Moving shadows are also strong cue for also strong cue for depth changedepth change
HeuristicHeuristic Ambiguous infoAmbiguous info
Shadow might reflect Shadow might reflect light source movementlight source movement
Assume light source Assume light source is constantis constant
Sun doesn’t move Sun doesn’t move that fastthat fast
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Experience and motion Experience and motion perception: Biological perception: Biological
motionmotion Dot walkersDot walkers We each have We each have
our own motion our own motion signaturesignature Recognition by Recognition by
motionmotion Experience Experience
influences motion influences motion perceptionperception
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Motion from structureMotion from structure Not only can Not only can
motion induce motion induce shape perceptionshape perception
Shape can induce Shape can induce motion motion perceptionperception
Top-down Top-down influencesinfluences FFA/IT —> MTFFA/IT —> MT
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Motion from structureMotion from structure Not only can Not only can
motion induce motion induce shape perceptionshape perception
Shape can induce Shape can induce motion motion perceptionperception
Top-down Top-down influencesinfluences FFA/IT —> MTFFA/IT —> MT
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How does the brain How does the brain represent motion?represent motion?
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V1: Simple motion V1: Simple motion detectorsdetectors
Directionally selectiveDirectionally selective E.g., right ward and upE.g., right ward and up
Small receptive fieldsSmall receptive fields Local not global motionLocal not global motion
Thus, respond to Thus, respond to components of a plaid, components of a plaid, not perceived directionnot perceived direction
Higher level info must Higher level info must override V1 simple override V1 simple motionmotion
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Designing a directionally Designing a directionally selective V1 neuronselective V1 neuron
Temporal componentTemporal component Built in delaysBuilt in delays
Neuron to neuron Neuron to neuron communication takes communication takes timetime
Timing of inhibition is Timing of inhibition is criticalcritical
Results in neuron Results in neuron liking right to left liking right to left motionmotion Not left to rightNot left to right
Delayed inhibition
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The brain’s motion eye: The brain’s motion eye: Area MT (V5)Area MT (V5)
Middle temporal area (MT)Middle temporal area (MT) Dorsal streamDorsal stream 90% of cells are directionally 90% of cells are directionally
selectiveselective Organized in directional Organized in directional
columnscolumns Like V1 orientation or IT shape Like V1 orientation or IT shape
columnscolumns Stimulation of column Stimulation of column
increases directional motion increases directional motion perceptionperception
100 times larger than V1 RFs100 times larger than V1 RFs Wide view of worldWide view of world Good for composite motionGood for composite motion
Human MT
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MT motion processing:MT motion processing:Random dot stimuliRandom dot stimuli
0%, 30%, and 100% coherence0%, 30%, and 100% coherence Use to determine monkey/human detection of Use to determine monkey/human detection of
directional motiondirectional motion
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How do we know MT supports motion How do we know MT supports motion perception?perception?
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Psychophysical and Psychophysical and neural motion response neural motion response
profilesprofiles Neurons Neurons
response relate response relate to perceptual to perceptual experience of experience of motion?motion?
MT neuron firing MT neuron firing rate parallels rate parallels perceptionperception
Neuron and observer motion detection
Random dots
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Stimulation of MT and Stimulation of MT and motionmotion
Neurons response Neurons response correlatedcorrelated with with perceptual perceptual experience of experience of motionmotion
Causally related?Causally related? Stimulation of MT Stimulation of MT
increasesincreases propensity to propensity to perceive motion in perceive motion in certain directioncertain direction
Right
Left
Proportion seen right directed motion
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After MT: After MT: Increasing Increasing
complexity/specificitycomplexity/specificity Medial superior Medial superior temporal (MST)temporal (MST) More specific More specific
patternspatterns Expansion/Expansion/
contractioncontraction Superior temporal Superior temporal
sulcus (STS)sulcus (STS) Biological motionBiological motion
Higherarchical Higherarchical organization and organization and sepcificity coding sepcificity coding extends to motionextends to motion
Neuron 1 Neuron 2
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Keeping the world stillKeeping the world still Given examples of motion w/out retinal Given examples of motion w/out retinal
changechange E.g., motion after effectsE.g., motion after effects
What about retinal change w/out motion?What about retinal change w/out motion? Eyes constantly make small fast movementsEyes constantly make small fast movements
Remember: World fades without these movementsRemember: World fades without these movements Why doesn’t world appear to shake?Why doesn’t world appear to shake?
Would get pretty nauseatingWould get pretty nauseating Vision needs to “correct” for eye movementsVision needs to “correct” for eye movements How does it do it?How does it do it?
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Corollary discharge Corollary discharge theorytheory
Integration of retinal stimulation and Integration of retinal stimulation and eye movementseye movements
Use motor signals to stabilize visionUse motor signals to stabilize vision Head movementHead movement Eye movementEye movement
How about movement without motor How about movement without motor signal?signal? (keep one eye closed) Push your open eye. (keep one eye closed) Push your open eye.
Gently please!Gently please! World moves!World moves!
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Corollary discharge Corollary discharge theorytheory
3 signals3 signals Motor (MS)Motor (MS) Image movement (IMS)Image movement (IMS) Corollary discharge (CDS) Corollary discharge (CDS)
Comparator (c)Comparator (c) Eye (IMS) and motor signals Eye (IMS) and motor signals
(MS) need to be compared(MS) need to be compared CDS is a copy of motor CDS is a copy of motor
signalsignal CDS and IMS cancel each CDS and IMS cancel each
otherother When both are present no When both are present no
signal sent to visual cortexsignal sent to visual cortex ——> No perception of > No perception of
motionmotion
Visual cortex
CDS
Motor cortex
IMS
C
MS
Eye
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Corollary discharge Corollary discharge theorytheory
Anytime CDS and IMS don’t co-occur —> perceive motionAnytime CDS and IMS don’t co-occur —> perceive motion IMS alone —> perceive motionIMS alone —> perceive motion
Veridical movementVeridical movement Eyes still, stimulus movesEyes still, stimulus moves
Illusory movement Illusory movement Pushing your eyePushing your eye Move image on retinaMove image on retinaw/out MS/CDSw/out MS/CDS
This theory makes interesting predictionsThis theory makes interesting predictions CDS alone should also result in motionCDS alone should also result in motion
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CDS: Moving after CDS: Moving after images!images!
CDS without IMSCDS without IMS Doesn’t often happenDoesn’t often happen No canceling of IMS No canceling of IMS
and CDSand CDS Should result in motion Should result in motion
perceptionperception After imagesAfter images
No IMSNo IMS Fatigued photoreceptors Fatigued photoreceptors
result in stationary result in stationary “stimulus”“stimulus”
MS/CDS without IMSMS/CDS without IMS After images moveAfter images move
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CDS alone results in CDS alone results in motion perceptionmotion perception
Track a flying birdTrack a flying bird No IMS, stabilized on retinaNo IMS, stabilized on retina MS/CDS without IMSMS/CDS without IMS CDS activates motion perception in CDS activates motion perception in
cortexcortex Paralyze eye musclesParalyze eye muscles
Can send MS but no eye movementCan send MS but no eye movement MS/CDS without IMSMS/CDS without IMS
Stationary events appear to moveStationary events appear to move
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““Real movement” Real movement” neuronsneurons
Higher order cortical Higher order cortical neurons (e.g. V3)neurons (e.g. V3) Bar moves through RFBar moves through RF
Move barMove bar Move eyesMove eyes
Retinal stimulation held Retinal stimulation held constantconstant
Respond most when not Respond most when not moving eyesmoving eyes
Real movement neuron
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The EndThe End
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