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Visuo-Motor Relationships:
Plasticity and Development
Demonstration: plasticity in relationship between vision
and movements
Ability to adapt to new relationships requires cerebellum
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.
Straight hand paths
People move their hand in a straight path even when
they can’t see their hand motion, and so can only rely
on proprioception.
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.
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.
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.
Won’t reach for targets beyond arm’s length.
Catching and anticipating target motion at 6 months.
Distance accuracy develops more slowly, improving by 7
months.
Increased use of visual feedback between 5 and 11 months
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Early reach movements
Initially use the trunk &
shoulder (proximal
joints) to reach for
objects; use elbow less
frequently.
When babies do make
large movements, can’t
control inter-segmental
dynamics. So hand
oscillates.
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
Development of reaching
Joint kinematics changes as well: coordination
among joints
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.
Reach and grasp development
Integrate sensorymotor signals
Pincer grasp
Calibrating visual
information to
form grip
Birth
Increased myelination of
corticospinal tracts
months
reach
onset
Direct hand
to object
fine tune
reach
Coordinated
torque patterns/
joint patterns
Continued
refinement
years
Role of Experience in
Development of Visuo-motor
coordination
Held & Hein
1
2
Both kittens get visual experience and motor experience
1. Visual experience correlated with motor
commands/proprioceptive feedback/vision of limbs
2. Gets both, but uncorrelated. Kitten 2 -abnormal visuomotor coordination.
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).
Role of Experience in
Development of Vision
Mike May, and Molyneux’s Question
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Neural control of Grasping
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
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.
Neural control of Grasping
Neural control of Grasping
Neurons in the
vPM also fires
when perceiving,
as well, as
producing grasping
movements!