1. The Organization and Planning of Movement Ch
The Organization and Planning of Movement Ch. 33, “Principles of Neural Science”, 5th Ed.
陳韋達 MD PhD
臺北榮總神經醫學中心 主治醫師
國立陽明大學醫學系/腦科所 副教授
哈佛大學醫學院麻省總醫院生醫影像中心 進修

2. Outline Motor action = the ultimate function of the sensory system
Step 1: Sensory input
Step 2: Sensorimotor transformation
Step 3: Motor output
Conscious processes are not necessary for movement control
Motor learning

3. Step 1: Sensory Inputs Extrinsic information Intrinsic
Eg. Spatial location of a target
Egocentric space
Mainly from visual or auditory input
Intrinsic
Kinematic information
Position, velocity and acceleration of the hand, joint angles, muscle lengths
From muscle spindles [Golgi tendon organs]
Kinetic information
The forces generated or experienced by our body
Reference

4. Egocentric space and coordinates
The choices of coordinate system in the brain is dependent on motor tasks and different stages of sensorimotor transformation

5. Difference sensory processing for action and perception
Optic ataxia
Visual agnosia
Reference

6. Step 2: sensorimotor transformation
Reference

7. kinematic vs. dynamic tasks
Dynamic and kinematic tasks involves different sensory modality
Dynamic: proprioception > vision
Kinematic: vision > proprioception
“Motion study” is a catch-all term for simulating and analyzing the movement of mechanical assemblies and mechanisms. Traditionally, motion studies have been divided into two categories: kinematics and dynamics. Kinematics is the study of motion without regard to forces that cause it; dynamics is the study of motions that result from forces. Other closely related terms for the same types of studies are multibody dynamics, mechanical system simulation, and even virtual prototyping.
Kinematic analysis is a simpler task than dynamic analysis and is adequate for many applications involving moving parts. Kinematic simulations show the physical positions of all the parts in an assembly with respect to the time as it goes through a cycle. This technology is useful for simulating steady-state motion (with no acceleration), as well as for evaluating motion for interference purposes, such as assembly sequences of complex mechanical system. Many basic kinematic packages, however, go a step further by providing “reaction forces,” forces that result from the motion.
Dynamic simulation is more complex because the problem needs to be further defined and more data is needed to account for the forces. But dynamics are often required to accurately simulate the actual motion of a mechanical system. Generally, kinematic simulations help evaluate form, while dynamic simulations assists in analyzing function.

8. Step 3: motor output (internal models)
Evidence of presence: motor equivalence
Reference

9. Step 3: motor output (internal models)
The forward model forms predicted behaviors and works as a guide for INITIAL motor output
The actual behavior starts from initial motor output (predicted behavior derived from feedforward model) then corrected by feedback controls
Reference

10. Movement errors and variability
The difference between desired and actual movement
Causes for movement errors
Neural noise of sensory neuron (input)
Inaccurate internal models
Neural noise of motor neuron (output)
Example 1: variability of constant force
Increased with force level
Example 2: speed-accuracy trade-off

11. Speed-Accuracy Trade-off

12. Fitt’s law: speed vs. accuracy
=the index of difficulty

13. Invariant and variant features of complex movements
Reference

14. Invariant feature Variant feature Variant feature
Hand path and speed are invariant (stereotypical) feature
Variant
feature

15. Movement Schemas
= The simple spatiotemporal elements of a complex movement
Reference

16. Bibliotics

17. Movement control Feedforward control (open-loop)
No sensory feedback is needed
Feedback control (closed-loop)
Sensory-dependent
Some movements only involve forward model
Saccade, deliberate reading, vestibular-ocular reflex (VOR)
Pros: save the time for sensorimotor delay
Cons: inaccuracy
Reference

19. Sensorimotor delay Sensory feedback is noisy and slow
The delayed information dose not reflect the the present state of the body and world
Two compensation strategies
Intermittency of movement
Prediction of changes in body states (better)
Reference

20. Prediction corrects sensorimotor delays
Reference

21. Observer model of motor prediction
Gain = the movement error

22. Motor learning
Most forms involve procedural or implicit learning (without consciously thinking)
Require different forms of sensory information
Improves motor control in novel situations
Motor control circuits are not static but modified throughout life
Reference

23. Machines can beat a chess master
but not the dexterity of a boy !