PSYCH 2220

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PSYCH 2220 Perception Lecture 7
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Go over midterm 1
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KEYWORDS -- Depth Perception
depth perception, artists cues (in order of
importance overlay, perspective, texture
gradient, size), playing card illusion, size
constancy, Ames room, impossible triangle, moon
illusion (1), stereopsis, parallax, stereograms
(demo), random dot stereograms (demo), disparity,
disparity tuned cells, Pulfrich's pendulum
(demo), accommodation (as a cue to depth), visual
cliff, autostereograms, motion-in-depth tuned
cells -- demo of stereopsis versus size
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Demo of stereopsis vs size
you
Cross eyed
2 coins
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FAR CELL
RIGHT EYE
FAR
NEAR
LEFT EYE
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NEAR CELL
RIGHT EYE
FAR
NEAR
LEFT EYE
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Visual motion
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The scrabble game by David Hockney
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Distinguishing eye movements from object
motion inflow/outflow autokinesis saccadic
suppression
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outflow
corollary discharge
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inflow
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PREDICTIONS
EXPERIMENTS
OUTFLOW
DATA
INFLOW
No movement
No movement
Active motion of real image
No movement
YES movement
Passive motion of real image
YES movement
YES movement
Active motion of after image
Passive motion of after image
YES movement
No movement
No movement
YES movement
Attempt to move paralyzed eye
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DEMO gently push eye
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No movement
YES movement
YES movement
No movement
YES movement
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Autokinesis
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Autokinesis auto movement When a light
appears to move around on its own.
outflow
corollary discharge
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DEMO saccadic suppression look in mirror
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Distinguishing eye movements from object
motion inflow/outflow outflow most
important autokinesis drift without
outflow saccadic suppression because
of corollary discharge
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OBJECT vs BACKGROUND
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INDUCED MOVEMENT
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CORTICAL BASIS OF MOTION PERCEPTION object
motion needs distance motion after
effect cortical responses clinical lesions to
area MT
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Why planes appear to move so slowly... Illustrate
what needs to be done to perceive object motion.
It needs distance.
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big thing far
small thing close
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Moon illusion 2 Why the moon moves with you...
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right
left
-

10
10
compare
0
no movement
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right
left
-

5
20
compare
15
movement left
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right
left
-

20
5
compare
-15
movement right
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right
left
AFTER ADAPT LEFT
-

10
7
compare
-3
movement right
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motion processing
visual cortex
motion processing
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Lesions in the medial temporal region of the
cortex cause MOTION BLINDNESS
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visual cortex
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visual cortex
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biological motion
visual cortex
biological motion
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CORTICAL BASIS OF MOTION PERCEPTION object
motion needs distance integration of info motion
after effect coding by comparison cortical
responses motion areas in the brain visual
cortex (simple cells) MT cells using corollary
discharge STS cells processing biological
motion clinical lesions to area MT motion areas
in the brain
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Self motion vision isnt all there is
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CUES TO MOTION PHYSICAL FORCES (picked up
by the vestibular system)
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Otoliths (ear stones)
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angular movement (rotation)
linear movement (translation)
Otoliths (ear stones)
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CUES TO MOTION physical forces TRANSLATION
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CUES TO MOTION physical forces ROTATION
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hair bending this way. causes depolarization
KINOCILIUM
afferent fibre
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Optic flow can generate VECTION
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Vection video
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Vision alone
Vestibular alone
Nystagmus eye movements
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Self motion and ALCOHOL 1 alcohol -gt canals 2
alcohol rises and moves the fluid 3 causes head
to feel tilting DOWN 4 eyes move UP 5 retina past
still world -gt visual world moved DOWN 6 visual
vection created suggesting head tiltingUP 7 head
up and down at same time? 8 Must be poisoned. 9
GET RID OF IT!!!!
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vision
gravity
MOTION SICKNESS in a boat cabin.
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MOTION SICKNESS
gravity
MOTION SICKNESS in a boat cabin.
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SELF MOTION vestibular system can help
distinguish external from self motion can remove
some motion due to self motion by eye movements
tends to keep background fixed on retina Visual
and vestibular cues can work together to tell you
about your self motion (guiding and navigating)
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MECHANISMS OF MOTION PROCESSING integration
across TIME and SPACE
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CRITICAL FLICKER FUSION FREQUENCY
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CRITICAL FLICKER FUSION FREQUENCY 50 hz in
centre 100 hz in periphery 200 hz in cats (hz
stands for Herz which is 1 cycle/second)
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CRITICAL FLICKER FUSION FREQUENCY tells us about
what period of TIME is integrated in calculating
motion (if something is at 50 hz it repeats
every 1/50th sec that is every 20
milliseconds) can be exploited in film and tv
and computers
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CRITICAL FLICKER FUSION FREQUENCY
Modern movies are projected at 48 hz with each
picture being shown twice (i.e. at 96
hz) Typical computer screen refresh is similar.
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STROBE DEMO
not fused!!!
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APPARENT MOTION Things have to be close
together in both SPACE and TIME to appear to move.
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APPARENT MOTION demo
on
LIGHT 1
off
on
LIGHT 2
off
close together in time
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• So now we need a model that will
• Explain normal motion perception
• Produce motion after effects
• Not work faster than CFFF
• Mix up apparent motion and real motion
• THERE ARE TWO CANDIDATES
• Inhibition model
• Delay model

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INHIBITION MODEL
A
B
C
Receptive fields
input cells
A
motion detector cells
B
C
C
B
A
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INHIBITION MODEL
A
B
C
Receptive fields
input cells
motion detector cells
comparison cell
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INHIBITION MODEL
Receptive fields
input cells
motion detector cells
comparison cell
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INHIBITION MODEL
A
B
C
Receptive fields
input cells
motion detector cells
comparison cell
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DELAY MODEL
medium delay
short delay
long delay
long delay
short
medium
medium
long delay
short
yes!!
no!!
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DELAY MODEL
Receptive fields
input cells
motion detector cells
comparison cell
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DELAY MODEL
Receptive fields
input cells
motion detector cells
comparison cell
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Summary of the motion class Distinguishing eye
movements from object motion Inflow/outflow
outflow most important autokinesis (drift
without outflow) saccadic suppression using
corollary discharge Object vs background Cortical
basis needs distance MAE cortical responses
(including biological motion) can be lost
clinically Self motion vestibular, canals,
otoliths, eye movements, vection Mechanisms
integrate over space and time CFFF/strobe,
motion after effect, apparent motion inhibition
model, delay model