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• Directs attention
– Motion attentionally salient
• Figure ground segregation
– Break camouflage
• Shape information
– 3D structure of object
• Interacting with environment
– Catching, avoiding
– Navigating
Motion Perception
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Information provided by motion
Camouflage
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3-D Structure from motion
Kinetic Depth Effect
Motion & Camouflage
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Motion Detector
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A Neural Circuit for Detection of Rightward Motion (Part 1)
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Computation of Visual Motion (cont’d)
• Need neurons tuned to motion
– Specific direction
– Specific speed
• How would you build a motion detector?
– Involves a change in position over time
– So start with two adjacent receptors separated by
fixed distance
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A Neural Circuit for Detection of Rightward Motion (Part 2)
• Apparent motion: The illusory impression of smooth
motion resulting from the rapid alternation of objects
that appear in different locations in rapid succession
• Web Demo
– Consistent with neural circuit described
– Does not need real motion in order to fire
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Computation of Visual Motion (cont’d)
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Global Motion Detector
•
• Aperture: An opening that allows only a partial view
of an object
– V1 cells
– respond to local edge or
contours
• Correspondence problem (motion): The problem
faced by the motion detection system of knowing
which feature in frame 2 corresponds to a particular
feature in frame 1
– may not correspond to
overall motion of object
•
• Aperture problem: The fact that when a moving
object is viewed through an aperture (receptive field),
the direction of motion of a local feature or part of the
object may be ambiguous
Global motion detectors
– MT cells
– respond to overall
motion of “objects”
– integrate info from
several local motion
detectors
• Web Demo
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Local motion detectors
The Medial Temporal Lobe
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Local vs. Global Motion
• Responses of neurons in V1 and MT to “plaids”
– V1 – respond to local motion
– MT – respond to global motion
V1
MT
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Computation of Visual Motion (cont’d)
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The Newsome and Pare Paradigm
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Computation of Visual Motion (cont’d)
• Role of MT in motion perception
• Experiment with monkeys (Newsome and Pare,
1988)
– Trained monkeys to respond to correlated dot
motion displays
– Web Demo
– MT areas of monkeys were lesioned
– Results: Monkeys needed about 10 times as many
dots to correctly identify direction of motion
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Computation of Visual Motion
• Perception of motion
• Banks of motion detectors
– Tuned to different directions
– Competing with one another
• Opponent process
• Similar to color
– Strongest response => motion that direction
• Motion aftereffect: The illusion of a stationary object
that occurs after prolonged exposure to a moving
object
– Existence of this effect implies an opponent process system, like that of color vision
– Stationary stimulus
• In balance
• No motion percept
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Evidence: Motion Aftereffects
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Eye Movements
• Eye movements:
– Smooth pursuit: Eyes move smoothly to follow
moving object
– Saccade: Rapid movement of eyes that change
fixation from one object or location to another
Waterfall illusion
– Superior colliculus: Structure in midbrain that
plays important role in initiating and guiding eye
movements
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Smooth Pursuit
• (a) fixate dot – move pencil
– Pencil sweeps across retina (is perceived to be moving)
– Dot stays at same place on retina (is perceived to be
stationary)
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Smooth Pursuit
• (b) fixate pencil as it moves
– Pencil stays at the same place on the retina (is perceived
to be moving)
– Dot sweeps across retina (is perceived to be stationary)
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Eye Movements (cont’d)
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• Why do we perceive the pencil to be in motion in the
first case, but perceive the dot to be stationary in the
second case?
Corollary Discharge Theory
• Motor system solves “problem” of why an object in
motion may appear stationary by sending out two
copies of each order to move eyes
– Because in one case there is an eye movement
– One copy goes to eye muscles
– Another (“efference copy”) goes to an area of
visual system that has been dubbed “comparator”
– Comparator can then “compensate” for image
changed caused by eye movement
– Reinterpret retinal motion in light of eye
movements
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The Comparator
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Evidence for Corollary Discharge Theory
• Ambiguous object motion
• Jiggling your eye
• Perceive afterimages moving through environment
• Paralyze eye muscles
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Eye Movements (cont’d)
• Saccadic eye movements
– Rapid eye movements from one location to another
– Results in saccadic suppression: Reduction of visual
sensitivity during saccade
– Eliminates “smear” from retinal image motion during
an eye movement
– Demonstration
• Look in mirror – fixate on one eye then the other
(see your eyes move? A: no)
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