Sensation & Perception
Ch. 7: Perception and Action
© Takashi Yamauchi (Dept. of Psychology, Texas A&M University)
Main topics
Ecological approach
Optic flow
The physiology of navigation
Skilled action
Linking sensory and motor functions
Mirror neurons
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Best Action film clip
• Just in case, if you were not part of the
history
– http://www.youtube.com/watch?v=ijXJRcAmI
mk&feature=related
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Perceptual theories
• Many perceptual theories are
about integrating top-down and
bottom-up processes
– Helmholtz’s unconscious inference
– Likelihood principle
Inverse projection problem
Bottom-up information is not enough to create 3D
perception.
Perception reconsidered
• J. J. Gibson’s ecological approach
– All the studies we have seen so far are
conducted in laboratory settings, in which
stationary stimuli were given.
– Perception is not a stationary experience.
– Perception should be studied as it occurs in the
natural environment.
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Perceptual experiments
• Muller Lyer Illusion
• Attention blink
• Visual search
Question:
• What information do perceivers use as they
move through the environment?
• One type of information is:
– Optic flow
• E.g., expansion/contraction of a scene (an optic array
that reaches the retina).
– We notice the ratio of expansion/contraction (a
gradient of flow).
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Optic flow and a gradient of flow
• A gradient of flow gives a strong cue for motion
and depth perception.
– How much the scene expands on your retina gives you
enough information to capture depth perception
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Demonstration:
http://www.reading.ac.uk/arl/clips/demo_of_displays.htm#opt
icflow
http://www.youtube.com/watch?v=ysGM3CfBVpU&feature=
related
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Some important characteristics of
optic flow
• Invariant information
– Gradient information remains constant under
different conditions.
– E.g., texture gradient
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Optic flow helps keep your balance
• Demonstration:
– Stand up and raise one foot, and stay balanced
while your eyes closed.
– Isn’t it difficult?
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Flow, Posture, and Balance
• Experiment by Lee and
Aronson
– 13- to 16-month-old
children placed in “swinging
room”
• In the room, the floor
was stationary but the
walls and ceiling swung
backward and forward
• The movement creates
optic flow patterns
– Children swayed forward in
response to the flow
patterns created in the
room
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The Physiology of Navigation
• Optic flow neurons - neurons in the medial
superior temporal area (MST) of monkeys
respond to flow patterns
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Neuron 1 in the monkey’s MST responds to an expanding stimulus
but not a stimulus with circular movement.
Neuron 2 responds to 14
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circular movement but not to expansion.
Skilled Actions
• Skilled actions partly arise from establishing a
coordination between sensory and motor systems.
• E.g., Somersaulting
– Bardy and Laurent found that expert gymnasts
performed worse with their eyes closed
• They use vision to correct their trajectory
• Novice gymnasts do not show this effect
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Physiological Links Between Sensory and
Motor Functions
• Optic ataxia
– Patients suffering from this syndrome produce
inaccurate reaching movements towards a
target or object in space.
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• Optic ataxia (3 min)
• http://www.youtube.com/watch?v=BkOb9F
R5Lgk
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Experiment by Schindler et al.
• Participants:2 groups
• Patients with parietal lobe damage and normal control
participants.
• Participants performed two tasks
• Bisection task - point to position between cylinders
• Reaching task - reach between cylinders and touch a gray
strip
Bisection task
In each trial, you saw
two cylinders that were
shifted different
positions.
You had to point a
place exactly midway
between the cylinders.
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Experiment by Schindler et al.
Trial 1
Bisection task
In each trial, you saw
two cylinders that were
shifted different
positions.
point
You had to point to a
place exactly midway
between the cylinders.
Trial 2
So, for each trial, you
had to point different
positions.
point
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Experiment by Schindler et al.
Trial 1
Reaching task
touch
In each trial, you saw
two cylinders that were
shifted different
positions.
You had to touch a gray
strip that were 20 cm
behind the cylinders.
Trial 2
touch
So, for each trial, you
had to extend your
hand to different
positions.
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Results
Trial 1
• Bisection task
– The patients with
parietal lobe damage
and normal control were
equally accurate
touch
• Reaching task
Trial 2
– The patients kept
reaching the same place
even though cylinders
were shifted in each
trial.
touch
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Interpretation
• The parietal lobe provides guidance for
movement.
• This mechanism operates unconsciously.
• But the patients with optic ataxia lost this
ability.
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Visual dominant vs. motor dominant
neurons
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Mirror neurons
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Mirror neurons
• Mirror neurons respond to a particular
“kind” of action (e.g., grasping) AND
observing someone doing the action.
The activity of a particular neuron in the
premotor area of a monkey.
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The activity of a particular neuron in the premotor area of a
monkey.
(a) This neuron responded when the monkey watched the
experimenter grasp the peanut.
(b) This neuron also responded when the monkey actually
grasped the peanut.
(c) This neuron did not respond when the monkey watched
the experimenter pick up the peanut with a pair of pliers..
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Mirror neurons
• Respond not only when you are doing a
particular action.
• But also when you watch someone doing it.
• This neuron gives you a general
characteristic of an action.
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What are mirror neurons for?
• Facilitate learning by imitation.
– Language development
– Skill learning
• Social interaction
– Empathy (understanding others or what others
think)
– Connecting with others
• Autism may be caused by the deficiency in
mirror neurons
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• Video clip from NOVA (PBS)
– 15 min
– http://www.pbs.org/wgbh/nova/sciencenow/320
4/01.html
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Creating action by activating
motor cortex
• motor cortex and motion: brain-machine
interface (4:30)
– Cathy Hutchinson has been unable to move her own arms
or legs for 15 years. But using the most advanced brainmachine interface ever developed, she can steer a robotic
arm towards a bottle, pick it up, and drink her morning
– http://www.youtube.com/watch?v=ogBX18maUiM&fe
ature=youtu.be
•
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