Motor Learning - Motor Control Theories

Motor program based theories
- Definition: A set of muscle commands that are organized in advance and executed without much feedback. This approach is often described as an “All or none” process, meaning that once initiated, the command is carried out to completion without any modification.
- Analogy: Comparable to a computer program, which executes predefined instructions.

Specific Instructions to Muscles:
- Determination of which muscles to use.
- Order of muscle activation.
- Timing and sequencing of muscle actions.
- Duration of actions.
CD Analogy:
- A compact disc (CD) defines which sounds occur and in what order, including the duration and timing of each sound, similar to how motor programs determine the sequence of muscle actions.

Reaction Time (RT):
- Observation: Reaction time increases as the complexity of the movement increases.
- Explanation: Longer RT indicates that more time is required for organizing the action.
- Complexity can be increased by:
- Adding elements to an action.
- Involving more limbs.
- Performing longer duration skills.
- Reference: Henry and Rogers (1960).
Deafferentation Experiments:
- Definition: Deafferentation refers to the cutting of sensory nerves so the Central Nervous System (CNS) no longer receives sensory feedback from the limbs.
- Question: What capabilities remain when deprived of feedback?

Experiment by Taub and Berman (1968):
- Method: Upper limbs of monkeys were deafferented.
- Results: Monkeys could still climb and chase, but struggled with fine motor controls (like eating). This suggests that commands for specific actions can be organized centrally, independent of feedback.
Muscle Activity Examination by Wadman et al. (1979):
- Method: Observed muscle activity during fast limb movements. Some movements were unexpectedly stopped.
- Findings: Even when movement stopped, a similar pattern and timing of muscle action was recorded for the first 120 ms, indicating pre-structured motor commands might be at play.

Novelty Problem:
- Question: How can new or novel movements be produced?
- Observation: Each movement can be considered novel in some way.
Storage Problem:
- Question: How can an infinite number of motor programs be stored and retrieved?
- Observation: There is limited storage capacity for motor commands.

Definition: A stored pattern of movement that allows modulation to adapt to environmental demands.
Characteristics:
- Invariant Features: Characteristics that do not change within a class of action; serves as an identifying signature.
- Parameters: Specific features that can be modified for performance; varies each time the action is performed.
Schema Theory by Schmidt (1988):
- Description: A set of rules that governs decision-making regarding motor actions.

Example of an Invariant Feature:
- Relative time or percentage of various phases in a movement.
Example of a Parameter:
- Overall or absolute duration or size of a movement.
Analogy: Music and dance rhythms demonstrate how invariant features (like a beat) and parameters (like tempo) function in performance.

Experiment by Hollerbach (1978):
- Method: Studied variations in movement amplitude by having subjects write words of different sizes.
- Results: Participants used similar movement patterns despite different sizes, with variations in force adapted for size.
Experiment by Raibert (1977):
- Method: Participants wrote sentences using different body parts (hands, mouth, foot).
- Results: Writing style remained consistent, suggesting the same GMP can vary based on effective agents (body parts).
Additional Experiment by Armstrong (1970):
- Method: Assessed movement time while producing direction-reverse movements at the elbow joint.
- Results: The first segment’s speed influenced the entire movement speed, but the pattern was preserved while adjusting the overall and relative times.
- Conclusion: Relative time is invariant, whereas overall time is variable.

Gait cycle evidence:
- Gait characteristics were tested against predictions of relative time invariance for actions controlled by a GMP.
Experiment by Shapiro et al. (1981):
- Method: Evaluated four components of a single step cycle at different speeds.
- Results: Relative time remained consistent across speeds for walking or running; however, differences arose between walking and running.

Historical Context:
- Emerged in the early 1980s, influencing motor control perspectives as a complex system that operates like other biological or physical systems.
Key Concepts:
- Non-linear dynamics: The governing laws that lead to changes in human coordination patterns.

End Product of Movements:
- Movements are perceived as products of biological systems comprising cooperating and sometimes competing subsystems.
Influence of Gravity:
- Recognizes how gravity can affect performance.
Subsystems:
- Internal factors (like effectors) and external factors (like environment and tasks).
Non-linear Changes:
- Examines in-phase (synchronous) vs. out-of-phase (antiphase) coordination.

Attractors:
- Defined as stable behavioral states towards which systems tend to move.
Order Parameters:
- Collective variables that describe movement patterns.
- Relative phase concepts like 2:1 and 3:1.
Control Parameters:
- Variables that can be manipulated within the system, often leading to phase transitions (e.g., speed and force).
Self-Organization:
- The natural tendency for systems to organize without external direction, illustrated through various patterns emerging under different constraints.

Definition: Functional synergies of muscles and joints that cooperate to produce specific actions.
Development: Through practice, experience, and genetics.
Function: Reduces degrees of freedom, allowing performance to persist even when facing limitations or injuries.

Definition: The integration of movement with relevant information from the environment.
Perceptual Components:
- Detection of critical invariant information from the surroundings.
Action Components:
- Movements that correspond to environmental specifications.

Summary Comment:
- Both motor program and dynamical systems theories play significant roles in understanding motor control.
- Emphasis on the necessity for a multifaceted approach, acknowledging both intrinsic (CNS) and extrinsic (environmental) factors influencing motor function.
Acknowledgment: Neither theory is free from flaws or limitations in comprehensively explaining motor control processes.