# 1 Psy280: Perception Prof. Anderson Department of Psychology Vision 7 Motion.

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1 Psy280: Perception Prof. Anderson Department of Psychology Vision 7 Motion

2 Optional papers: QuALMRI Question/hypothesis Question/hypothesis Alternative Alternative Logic Logic Method Method Results Results Inferences Inferences Detailed description on website Detailed description on website

3 Part 2: Perceiving Size Not as simple as size of stimulus on retina Not as simple as size of stimulus on retina Visual angle: retinal projection depends on distance Visual angle: retinal projection depends on distance Different physical Different physicalsize Same retinal Same retinalProjection Bigger stimulus further away Bigger stimulus further away = visual angle to closer smaller stimulus = visual angle to closer smaller stimulus

4 Size constancy Perception of size remains constant Perception of size remains constant Despite different visual angle/retinal size Despite different visual angle/retinal size

5 Size distance scaling Perceived size = retinal image size X distance from object Perceived size = retinal image size X distance from object Without depth information Without depth information Perceived size = retinal image size Perceived size = retinal image size 2 x distance but same retinal size = 2 x perceived size

6 Emmert’s law Perceived size of an after image depends on depth perception (consistent with S = R x D) Perceived size of an after image depends on depth perception (consistent with S = R x D)

7 Size-depth illusions Moon appears larger on the horizon than the sky Moon appears larger on the horizon than the sky Same retinal size Same retinal size Difference in magnitude Difference in magnitudeestimation Horizon provides depth cues Horizon provides depth cues Sky does not Sky does not Appear flattened Appear flattened

8 Motion

9 Motion: Frames of reference 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 : 24000 miles / 24 hours = 1000 miles/hr Motion due to earth : 24000 miles / 24 hours = 1000 miles/hr Earth circles the sun: 2 pi 93,000,000 miles / 8760 hours = 66700 miles/hr Earth circles the sun: 2 pi 93,000,000 miles / 8760 hours = 66700 miles/hr Sun circles the galaxy (30,000 light year = r) every 1 / 4 billion years 1.76 x 10 17 miles / 2.19 x 10 12 hr = 80400 miles/ hr Sun circles the galaxy (30,000 light year = r) every 1 / 4 billion years 1.76 x 10 17 miles / 2.19 x 10 12 hr = 80400 miles/ hr Is there anything that is not moving? Is there anything that is not moving? Must be careful about our description of motion Must be careful about our description of motion Moving relative to what reference frame? Moving relative to what reference frame?

10 Animism: Worshiping the light Divides living organisms Divides living organisms Animals vs plants Animals vs plants Capacity for voluntary movement Capacity for voluntary movement vs phototropism vs phototropism Co-evolution Co-evolution Organisms that move Organisms that move Evolution of a capacity to sense movement Evolution of a capacity to sense movement

11 Invisible motion: Morning glory 5 AM to 7PM 5 AM to 7PM Open in morning Open in morning Pollination by diurnal insect Pollination by diurnal insect Dies in afternoon Dies in afternoon Motion too slow to notice even dramatic change Motion too slow to notice even dramatic change Our visual system are tuned to events that move more quickly Our visual system are tuned to events that move more quickly E.g., Animals (fast) not plants (slow) E.g., Animals (fast) not plants (slow)

12 Motion and change detection Visual motion is sensing change in retinal image (sort of) Visual motion is sensing change in retinal image (sort of) As duration between changes increases perception of motion decreases As duration between changes increases perception of motion decreases Motion is a perceptual adaptation for detection of change, otherwise invisible to the eye Motion is a perceptual adaptation for detection of change, otherwise invisible to the eye Can’t tell difference across space Can tell difference across time

13 Motion and the retinal image Change in image intensity (luminance) over time Change in image intensity (luminance) over time Dark to light Dark to light Light to dark Light to dark Difference image

14 Illusory movement: Apparent motion Luminance change Luminance change No physical continuity No physical continuity Infer motion where none is present Infer motion where none is present Critical temporal/spatial parameters Critical temporal/spatial parameters Simultaneous flicker Simultaneous flicker <10-30 ms interval <10-30 ms interval Perceive 2 events Perceive 2 events Motion Motion ~60 ms interval ~60 ms interval Perceive 1 event Perceive 1 event

15 Not just simple luminance change: 2nd order motion First-order motion First-order motion Change in luminance boundary Change in luminance boundary Luminance change doesn’t explain all motion Luminance change doesn’t explain all motion Second-order motion Second-order motion Motion but no luminance boundary Motion but no luminance boundary Not net luminance change Not net luminance change Object disappears when motion stops Object disappears when motion stops

16 Second order motion: Illusory shapes and motion No luminance boundary for low-level motion detectors to use No luminance boundary for low-level motion detectors to use Motion perception must rely on other top- down/higher-order influences Motion perception must rely on other top- down/higher-order influences Simple luminance based motion detectors can’t explain all of motion perception Simple luminance based motion detectors can’t explain all of motion perception

17 Simple luminance detectors won’t do: The aperture problem Narrow view of world through small receptive fields (RF) Narrow view of world through small receptive fields (RF) Ambiguity of direction of motion Ambiguity of direction of motion Need additional info for accurate motion sensing Need additional info for accurate motion sensing Edges or texture Edges or texture

18 The aperture problem Looking at motion through the window of one neuron Looking at motion through the window of one neuron RF represents horizontal motion RF represents horizontal motion Global scene has different motion Global scene has different motion Local computations don’t necessarily explain motion Local computations don’t necessarily explain motion Need to share information across neurons Need to share information across neurons Perceived motion

19 Motion perception: More than the sum of its parts The underlying mechanism involves signals at different retinal locations being integrated to arrive at global motion signals

20 Motion integration at the same retinal location: Plaids First order low-level motion detectors First order low-level motion detectors Respond to each component of motion (horizontal and vertical) Respond to each component of motion (horizontal and vertical) Motion integration Motion integration Don’t perceive either Don’t perceive either Create common directional signal Create common directional signal Like force vectors Like force vectors Down & left moving plaid Down & left moving plaid

21 Motion detection as an opponent process Like colour vision: Red-green, blue-yellow Like colour vision: Red-green, blue-yellow Motion Motion Up-down Up-down Left-right Left-right Spiral in-out Spiral in-out Enhances “motion contrast” Enhances “motion contrast”

22 Motion after effect Reversing waterfall Reversing waterfall Fatigue your direction sensitive neurons Fatigue your direction sensitive neurons See opposite motion where there is none See opposite motion where there is none Explanation Explanation No motion No motion Direction selective cells produce equal responses Direction selective cells produce equal responses No longer equally oppose each other No longer equally oppose each other E.g., Adapt to red— >perceive green E.g., Adapt to red— >perceive green

23 Spiral motion after effect: Disfiguring Brad 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)!

24 Direction repulsion: Lateral inhibitory influences in motion Vertical and 45 Vertical and 45 degree movement Interact to enlarge directional disparity Interact to enlarge directional disparity Evidence of lateral inhibitory interactions between motion detectors Evidence of lateral inhibitory interactions between motion detectors Enhancement of directional “contrast” Enhancement of directional “contrast” Motion “mach bands” Motion “mach bands” Actual Perceived

25 Perceptual organization: Structure from motion Motion perception not used just to assess stimulus movement Motion perception not used just to assess stimulus movement Can define “objects” Can define “objects” Laws of organization Laws of organization Common fate Common fate Things that move together belong to same object Things that move together belong to same object A camouflaged animal is difficult to see until it moves A camouflaged animal is difficult to see until it moves Not just knowledge based Not just knowledge based Can see novel objects Can see novel objects

26 Structure from motion: Kinetic depth Can define depth Can define depth What motion cues define depth? What motion cues define depth? Parallax Parallax Differing dot velocity Differing dot velocity Track single dot Track single dot See velocity change See velocity change Infer depth from motion Infer depth from motion

27 Kinetic depth: Shadow motion Moving shadows are also strong cue for depth change Moving shadows are also strong cue for depth change Heuristic Heuristic Ambiguous info Ambiguous info Shadow might reflect light source movement Shadow might reflect light source movement Assume light source is constant Assume light source is constant Sun doesn’t move that fast Sun doesn’t move that fast

28 Experience and motion perception: Biological motion Dot walkers Dot walkers We each have our own motion signature We each have our own motion signature Recognition by motion Recognition by motion Experience influences motion perception Experience influences motion perception

29 Motion from structure Not only can motion induce shape perception Not only can motion induce shape perception Shape can induce motion perception Shape can induce motion perception Top-down influences Top-down influences FFA/IT —> MT FFA/IT —> MT

30 Motion from structure Not only can motion induce shape perception Not only can motion induce shape perception Shape can induce motion perception Shape can induce motion perception Top-down influences Top-down influences FFA/IT —> MT FFA/IT —> MT

31 How does the brain represent motion?

32 V1: Simple motion detectors Directionally selective Directionally selective E.g., right ward and up E.g., right ward and up Small receptive fields Small receptive fields Local not global motion Local not global motion Thus, respond to components of a plaid, not perceived direction Thus, respond to components of a plaid, not perceived direction Higher level info must override V1 simple motion Higher level info must override V1 simple motion

33 Designing a directionally selective V1 neuron Temporal component Temporal component Built in delays Built in delays Neuron to neuron communication takes time Neuron to neuron communication takes time Timing of inhibition is critical Timing of inhibition is critical Results in neuron liking right to left motion Results in neuron liking right to left motion Not left to right Not left to right Delayed inhibition

34 The brain’s motion eye: Area MT (V5) Middle temporal area (MT) Middle temporal area (MT) Dorsal stream Dorsal stream 90% of cells are directionally selective 90% of cells are directionally selective Organized in directional columns Organized in directional columns Like V1 orientation or IT shape columns Like V1 orientation or IT shape columns Stimulation of column increases directional motion perception Stimulation of column increases directional motion perception 100 times larger than V1 RFs 100 times larger than V1 RFs Wide view of world Wide view of world Good for composite motion Good for composite motion Human MT

35 MT motion processing: Random dot stimuli 0%, 30%, and 100% coherence 0%, 30%, and 100% coherence Use to determine monkey/human detection of directional motion Use to determine monkey/human detection of directional motion How do we know MT supports motion perception? How do we know MT supports motion perception?

36 Psychophysical and neural motion response profiles Neuronal response related to perceptual experience of motion? Neuronal response related to perceptual experience of motion? MT neuron firing rate parallels perception MT neuron firing rate parallels perception Neuron and observer motion detection Random dots

37 Stimulation of MT and motion Neurons response correlated with perceptual experience of motion Neurons response correlated with perceptual experience of motion Causally related? Causally related? Stimulation of MT increases propensity to perceive motion in certain direction Stimulation of MT increases propensity to perceive motion in certain direction Right Left Proportion seen right directed motion

38 After MT: Increasing complexity/specificity Medial superior temporal (MST) Medial superior temporal (MST) More specific patterns More specific patterns Expansion/ Expansion/contraction Superior temporal sulcus (STS) Superior temporal sulcus (STS) Biological motion Biological motion Higherarchical organization and sepcificity coding extends to motion Higherarchical organization and sepcificity coding extends to motion Neuron 1 Neuron 2

39 Keeping the world still Examples of motion w/out retinal change Examples of motion w/out retinal change E.g., motion after effects E.g., motion after effects What about retinal change w/out motion? What about retinal change w/out motion? Eyes constantly make small fast movements Eyes constantly make small fast movements Remember: World fades without these movements Remember: World fades without these movements Why doesn’t world appear to shake or move when we move our eyes? Why doesn’t world appear to shake or move when we move our eyes? Would get pretty nauseating Would get pretty nauseating Vision needs to “correct” for eye movements Vision needs to “correct” for eye movements How does it do it? How does it do it?

40 Corollary discharge theory Integration of retinal stimulation and eye movements Integration of retinal stimulation and eye movements Use motor signals to stabilize vision Use motor signals to stabilize vision Head movement Head movement Eye movement Eye movement How about movement without motor signal? How about movement without motor signal? (keep one eye closed) Push your open eye. Gently please! (keep one eye closed) Push your open eye. Gently please! World moves! World moves!

41 Corollary discharge theory 3 signals 3 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 (MS) need to be compared Eye (IMS) and motor signals (MS) need to be compared CDS is a copy of motor signal CDS is a copy of motor signal CDS and IMS cancel each other CDS and IMS cancel each other When both are present no signal sent to visual cortex When both are present no signal sent to visual cortex —> No perception of motion —> No perception of motion Visual cortex CDS Motor cortex IMS C MS Eye

42 Corollary discharge theory Anytime CDS and IMS don’t co-occur —> perceive motion Anytime CDS and IMS don’t co-occur —> perceive motion IMS alone —> perceive motion IMS alone —> perceive motion Veridical movement Veridical movement Eyes still, stimulus moves Eyes still, stimulus moves Illusory movement Illusory movement Pushing your eye Pushing your eye Move image on retina Move image on retina w/out MS/CDS This theory makes interesting predictions This theory makes interesting predictions CDS alone should also result in motion CDS alone should also result in motion

43 CDS: Moving after images! CDS without IMS CDS without IMS Doesn’t often happen Doesn’t often happen No canceling of IMS and CDS No canceling of IMS and CDS Should result in motion perception Should result in motion perception After images After images No IMS No IMS Fatigued photoreceptors result in stationary “stimulus” Fatigued photoreceptors result in stationary “stimulus” MS/CDS without IMS MS/CDS without IMS After images move! After images move!

44 CDS alone results in motion perception Track a flying bird Track a flying bird No IMS, stabilized on retina No IMS, stabilized on retina MS/CDS without IMS MS/CDS without IMS CDS activates motion perception in cortex CDS activates motion perception in cortex Paralyze eye muscles Paralyze eye muscles Can send MS but no eye movement Can send MS but no eye movement MS/CDS without IMS MS/CDS without IMS Stationary events appear to move Stationary events appear to move

45 Motion perception is more than movement across the retina Perception more than what retina tells us Perception more than what retina tells us So what’s new! So what’s new! Can dissociate retinal change and motion perception Can dissociate retinal change and motion perception Retinal change without motion perception Retinal change without motion perception Move eyes across stationary scene Move eyes across stationary scene World doesn’t move despite radical retinal shift World doesn’t move despite radical retinal shift Motion perception without retinal change Motion perception without retinal change Track a moving object Track a moving object No movement across retina: Powerful perception of motion No movement across retina: Powerful perception of motion

46 “Real movement” neurons Higher order cortical neurons (e.g. V3) Higher order cortical neurons (e.g. V3) Bar moves through RF Bar moves through RF Move bar Move bar Move eyes Move eyes Retinal stimulation held constant Retinal stimulation held constant Respond most when not moving eyes Respond most when not moving eyes V1? V1? Real movement neuron

47 The End

48 MT and virtual motion MT responsive to virtual motion MT responsive to virtual motion Motion after effects or illusory motion Motion after effects or illusory motion No retinal change No retinal change Stimulate MT—>voila! Motion Stimulate MT—>voila! Motion Time course of MT activation follows motion after effect

49 3D motion: More motion heuristics Visual stimulus is ambiguous Visual stimulus is ambiguous Multiple interpretations Multiple interpretations Which is visual system attracted to? Which is visual system attracted to? Vision assumes movement of rigid objects Vision assumes movement of rigid objects

50 Intelligence of motion perception 1. Notice oscillation in direction of motion: Due to single reversal 2. Look at with and without blinking your eyes

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