Perception of Motion and
Movement
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
1
Quiz: List five ways to make a spot
of light appear to move:
1. Move the light
2. Apparent Motion
•
Turn off the light, turn on another
•
Move a large framing object
•
View a dim light in a very dark room
•
Move something for a long time - then look at the
light
3. Induced Motion
4. Auto kinetic effect
5. Movement aftereffect
6. (Change the intensity of the light)
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Say at V1 the neurons detected this
pattern
Orientation
Positions across retina
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PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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and a moment later the neurons
detected this pattern
Orientation
Positions across retina
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PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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What could be the source of this
motion?
Orientation
Positions across retina
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Orientation
Positions across retina
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Sources of movement for the eyebrain system
• motion across the retina
– object moving or eye or head or body moving?
• eye movement
– tracking an object or just looking around?
• head movement
• body movement
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Categorize into four possibilities
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World in motion:
Eyes in
motion:
No
No
Yes
Static
Vision
Retinal Motion
Eye/Body
Yes
movement
Tracking
Gregory: Inflow/Outflow
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Retinal (image) motion
• movement of light across retina
• sensitivity found in all animals
– not all animals see static images
– all animals see motion
• motion detected by some animals in retina
– house fly, frog
• motion detected by some animals in brain
– cats, humans
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Uses of motion information
1. Relative velocity of observer and environment
•
direction of heading, time to contact
2. Segmentation of figure from ground
•
disruption of camouflage techniques
3. Recovery of 3D parameters
•
•
motion parallax (3D depth)
kinetic depth (3D shape)
4. Object identification
•
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humans, friend/foe
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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1. Relative velocity of observer and
environment
• speed and direction of objects/observer
• optic flow - pattern of motion in image when
observer moves
Centre of expansion ------>
= direction of heading
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Optic flow
• used to determine
– direction of heading
– time to collision
– approach/avoidance
• types of optic flow caused by global motion
– expansion/contraction (collision?)
– translation
– rotation
• Gibsonian approach uses optic flow a lot
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
Optic
flow
demo
11
2. Segmenting figure from ground
• Figure: object that draws our attention
• Ground: non-moving dots/contours/blobs
• Gestalt law of Common Fate
– items that move together belong together
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Common
fate
demo
From http://www.human.pefri.hr/~bsremec/figure_motion.html
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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3. Recovering three-dimensional
shape
• Retinas can only record 2D projection of world
• depth dimension is lost
• Use motion to recover some 3D information
• different information from different views
• combine into a single 3D model (hypothesis)
• Two methods:
a. motion parallax
b. kinetic depth
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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•
a. Motion parallax:
• different viewpoints recover depth
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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•
a. Motion parallax:
• different viewpoints recover depth
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PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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b. Kinetic depth
• different views recover shape
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QuickTime™ and a
Animation decompressor
are needed to see this picture.
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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4. Object identification
• motion pattern identifies object
• visual form masked by “stuff”, such as
•
•
•
•
•
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trees, leaves
smoke
bad vision
distance
low lighting
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Davis
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QuickTime™ and a
Video decompressor
are needed to see this picture.
From http://www-white.media.mit.edu/~jdavis/
MotionTemplates/motiontemplates.html
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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PLD
1/29/2002
QuickTime™ and a
PNG decompressor
are needed to see this picture.
From my research!
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Point light displays (Johansson)
• separate visual form and motion pattern
• robust detection even with distractors
– separation of figure and ground
• accurate determination
– sex, friends, animals, emotional affect, action
• humans only really good at recognizing humans
– relies on human motor control system
– “if I could move like that then it could be like me”
• but humans are pretty good at recognizing
everything
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Finally
• What was the purpose of this presentation?
• Which question remains unanswered?
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Detecting image motion
It moved! It moved!
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Motion detection versus perception
• detection: low level process
– low level, like edge detection
• perception: higher level process
– high level, like object identification
• how do we know that we have specific neurons
for motion detection?
• how do we know that we have specific centers
for motion perception?
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Specific neurons for motion
detection
• motion after effect
– similar to colour after effect
(“negative” after starring at image)
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Motion aftereffect
• shape not affected
• adaptation to motion
independent of shape
• separate systems for
motion and shape!
(and colour!)
1/29/2002
QuickTime™ and a
Animation decompressor
are needed to see this picture.
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
26
Neurons specialized for motion
detection
• 1960-1970s
– frogs (“bug”, “predator” detectors)
– house fly (optic flow)
– rabbit
– cat (string, yarn -- just kidding)
– monkey
• model proposed: Reichardt detector
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Reichardt detector
• correlator + two different inputs
– one input has a delay
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Input 1
Input 2
Motion
detected
delay
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Directionally sensitive
• fires for change in one direction, not in other
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Temporally sensitive
• fires for change over particular interval
• change too fast: first spike arrives too late
• change too slow: first spike arrive too early
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Input 1
Input 2
won't fire:
only 1 signal
arrives
delay
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Take home message
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only a particular speed and direction
sets off any particular Reichardt detector
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Apparent Motion (NOT phi motion)
1. A visible item suddenly disappears
2. A new item appears soon afterwards at
neighboring location
• Perception:
the original item “moves” to a new location
• Where have you seen this?
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Apparent Motion (NOT phi motion)
1. A visible item suddenly disappears
2. A new item appears soon afterwards at
neighboring location
• Perception:
the original item “moves” to a new location
• Where have you seen this?
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Apparent motion constraints
1.
2.
3.
4.
5.
not influenced by cognition - pops out
short spatial range (< 0.25°)
short temporal range (< 80ms)
many objects at once
very much like “real” motion detection
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Explanation of apparent motion
• Reichardt detector
– can detect continuous motion
1/29/2002
Input 1
Input 2
Motion
Motion
detected
detected
delay
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
35
Explanation of apparent motion
• Reichardt detector
– can detect sudden “jumps”
– cannot distinguish them
1/29/2002
Motion
detected
Input 1
Input 2
delay
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
36
Applications of apparent motion
• Movies and Television
– Reichardt detectors cannot distinguish “real” from
“artificial” motion
• Present a sequence of frames/static images
– seen the same as real motion
• Requires proper timing
– separation between frames < 80ms
• Movies: 24 FPS = 1/24 seconds = 41ms
• TV: 30 FPS = 1/30 = 33ms
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Importance of context
• Reichardt detectors do not completely account
for motion perception
• Just as lateral inhibition does not completely
account for brightness perception
• Context counts!
– Apparent motion of the human body
– Perception of motion can occur (or be
misperceived) -> induced motion
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Apparent motion of the human
body
Shiffrar and Freyd (1990)
1. image of human in one pose
2. delay
3. image of human in second pose
4. chose from one of four motion paths
results: physically plausible paths require delays
approximately equal to real world motion
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Shiffrar and Freyd: Implications
• brain takes into account typical movement
patterns
• brain “knows” how long a movement should
take
• brain uses motor control and perception
centers to form perceived motion path
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Downing et al (2001)
• EBA: extrastriate body area
• active when viewing human bodies
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PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Is object/world moving or eye??
• see Gregory pp 99-105
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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Finally
• What was the purpose of this presentation?
• Which question remains unanswered?
1/29/2002
PSYC202-005, Term 2, Copyright 2002 Jason Harrison
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