Psy280: Perception

1

Psy280: Psy280: PerceptionPerception

Prof. AndersonProf. AndersonDepartment of PsychologyDepartment of Psychology

Vision 7Vision 7MotionMotion

2

Optional papers: Optional papers: QuALMRIQuALMRI

QuQuestion/hypothesisestion/hypothesis AAlternativelternative LLogicogic MMethodethod RResultsesults IInferencesnferences

Detailed description on websiteDetailed description on website

3

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?

4

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

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

5

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)

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

6

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

QuickTime™ and aGraphics decompressorare needed to see this picture.

7

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

Difference imageQuickTime™ and aGraphics decompressorare needed to see this picture.

8

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

QuickTime™ and aGIF decompressorare needed to see this picture.QuickTime™ and aGIF decompressorare needed to see this picture.

9

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

QuickTime™ and aAnimation decompressorare needed to see this picture.

10

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


11

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

12

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


QuickTime™ and aAnimation decompressorare needed to see this picture.QuickTime™ and aAnimation decompressorare needed to see this picture.

13

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

14

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



15

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”

16

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


17

Spiral motion after Spiral motion after effect: Disfiguring Bradeffect: Disfiguring Brad

QuickTime™ and aGIF decompressorare needed to see this picture.

• 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)!

18

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”


Actual Perceived

19

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

QuickTime™ and aVideo decompressorare needed to see this picture.QuickTime™ and aVideo decompressorare needed to see this picture.

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.

20

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


21

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


QuickTime™ and aCinepak decompressorare needed to see this picture.

22

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


23

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

24

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

25

How does the brain How does the brain represent motion?represent motion?

26

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

27

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

28

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

29

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

QuickTime™ and aVideo decompressorare needed to see this picture.QuickTime™ and aVideo decompressorare needed to see this picture.QuickTime™ and aVideo decompressorare needed to see this picture.

How do we know MT supports motion How do we know MT supports motion perception?perception?

30

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

31

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

32

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

33

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?

34

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!

35


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

36


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

37

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

38

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

39

““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

40

The EndThe End

Documents

Psy280: Perception