VisuoMotor Relationships: Plasticity and Development

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Visuo-Motor RelationshipsPlasticity and
Development
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Demonstration plasticity in relationship
between vision and movements
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Ability to adapt to new relationships requires
cerebellum
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Why do we need to retain plasticity for new
visuo-motor relationships?
1. Need to adjust to changes in body size during
development.
2. Need to adjust to damage/aging.
3. Need to adjust to environmental changes eg
ice, loads etc.
4. Need to learn arbitrary mappings for tool use
etc.
5. Need to acquire new motor skills.
6. Visuo-motor coordination is a computationally
difficult problem for the brain. Need flexibility
to correct errors.
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Straight hand paths
People move their hand in a straight path even
when they cant see their hand motion, and so can
only rely on proprioception.
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Straight hand paths
Paths are straight even when the arm is
loaded. Even when the arm is perturbed by forces
acting on it, people learn to make straight hand
paths.
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Grasping
Reaching and grasping actions require close
coordination, but depend on different kinds of
visual information... Reaching egocentric
(where is object relative to me) Transform visual
information about object location into movement
direction. Grasping object-centred Transform
visual information about object properties (shape
and size) into commands for grasping movements.
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Development of reaching
Within first 2 weeks, already directing arm
towards objects. Some crude control of reach
direction. Improves by the 5th month
consistently touch targets. Wont reach for
targets beyond arms length. Catching and
anticipating target motion at 6 months. Distance
accuracy develops more slowly, improving by 7
months.
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Increased use of visual feedback between 5 and 11
months
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Early reach movements
Initially use the trunk shoulder (proximal
joints) to reach for objects use elbow less
frequently. When babies do make large movements,
cant control inter-segmental dynamics. So hand
oscillates.
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Development of reaching
Between 5 and 9 months see many changes to
kinematics
1) Straightening of the hand path
2) Reduced number of submovements 3) Reduced
movement time
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Development of reaching
Joint kinematics changes as well coordination
among joints
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Development of grasping
Newborns have grasp reflex (clasp object brought
against the palm) disappears by 6 months. 5
months hand does not orient to object until
contact 9 months hand orients prior to contact
(note visual information about orientation is
available at 2 months). Pre-shape for object
size. Still adjusting grip force by 7-8 years
(grip force larger for larger objects). Use
palmar grasp until about 12 months then use
fingers to grasp. Corresponds to rapid increase
in the rate of myelination of corticospinal
tracts at 12 months responsible for distal
musculature.
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Reach and grasp development
Calibrating visual information to form grip
Integrate sensory-motor signals
Pincer grasp
Birth
Continued refinement
Increased myelination of corticospinal tracts
years
months
reach onset
fine tune reach
Coordinated torque patterns/ joint patterns
Direct hand to object
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Role of Experience in Development of Visuo-motor
coordination
Held Hein
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• Both kittens get visual experience and motor
  experience
• Visual experience correlated with motor
  commands/proprioceptive feedback/vision of limbs
• Gets both, but uncorrelated. Kitten 2 -abnormal
  visuo-motor coordination.

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Adaptation to different relation between vision
and movement.

• George Stratton
• Wore inverting lens for 8 days

If he saw an object on the right he would reach
with his right hand and discover he should have
reached with his left. He could not feed himself
very well, could not tie his shoelaces, and found
himself severely disoriented. His image of his
own body became severely distorted. At times he
felt his head had sunk down between his
shoulders,and when he moved his eyes and head the
world slid dizzyingly around.
As time went by Stratton achieved more effective
control of his body. If he saw an object on the
right he would reach with his left hand. He could
accomplish normal tasks like eating and dressing
himself. His body image became almost normal and
when he moved his eyes and head the world did not
move around so much. He began to feel as though
his left hand was on the right, and his right
hand on the left. If this new location of his
body was vivid, the world appeared right side up,
but sometimes he felt his body was upside down in
a visually right-side-up world. After removing
the prisms, he initially made incorrect reaching
movements. However, he soon regained normal
control of his body.
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Adaptation to different relation between visual
and movement.

• George Stratton
• Wore inverting lens for 8 days
• Believed that we learn visual directions by
  associating visual experiences with other forms
  of sensory feedback (e.g. proprioceptive).
• Alternatively
• Adaptation results from learning correlation
  betweeen vision and actively generated motor
  commands (Held, 1965).

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Role of Experience in Development of Vision
Mike May, and Molyneuxs Question
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Neural control of Grasping
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Neural control of Grasping
Both vPM and AIP neurons fire for specific hand
actions/objects. For example, this neuron
prefers a precision grip.
Precision grip
Power grip
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Neural control of Grasping
vPM neurons fire for grasping movements made in
the light and dark. In contrast, AIP neurons fire
far less when moving in the dark, and in general,
AIP has more visual neurons than vPM.
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Neural control of Grasping
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Neural control of Grasping
Neurons in the vPM also fires when perceiving, as
well, as producing grasping movements!