Open Loop Control
Input - Executive - Effector
Movement executive sends a command to the effectors, no use of sensory information to guide movement. Movements shorter than 150-200ms.
Closed Loop Control
Input - Executive - Effector - Sensory Feedback
Sensory information from the effectors is fed back to the executive to inform the control centre about the movement. Movements longer than 200ms.
Reflex theories of motor control
Reflexes form the basis of all movements (Sherrington).
Complex movements are enacted by response chaining. Response chaining/reflex chaining.
Limitations of Reflex Theories
- Don’t allow for proactive action
- Poor account for open loop control
- Some movements don’t require afferent input
Hierarchical theories of motor control
Human motor systems organised like a hierarchy. Assumes all aspects of voluntary movement planning and execution are the sole responsibility of higher cortical centres.
Perceive - decide - control
Motor Programmes
Representations of movement stored in memory
Generalised Motor Programs
Invariant parameters - relative sequencing of sub-movements, relative timing, relative forces
Variant parameters - specific motor units, absolute timing, absolute forces
Schemas
Memory representations of movement parameters. If the movement goes wrong you immediately try to find a way that next time you can succeed in the movement.
Motor response schema
Relationship between motor response and outcome
Recognition Schema
Relationship between sensory experience and outcome
Size principle
Depending on the amount of force required for movement, we recruit motor units dependent on the minimum amount required for movement.
Limitations of hierarchical theories
- Cannot explain how direct perception works
- Cannot explain self-organising systems
Assumptions of Dynamical/Ecological theories of motor control
- Human movement control is complex and dynamic
- Human perceptual motor system is capable of self-organising via interacting constraints
- Perception of affordances is direct via energy flows from environment
Perceptual motor landscape
A manifold of all the possible movement possibilities available to an individual
Self-organisation
Natural tendency for the human perceptual motor system to settle into attractors
Attractors
Stable and functional patterns of organisation exhibited by the human perceptual motor system
Order parameters
Collective behaviour of the systems many components
Control parameters
A parameter of internal or external origin that when manipulated controls the system in a nonspecific fashion
Stability/Instability
A qualitative state describing the tendency of a system to remain in a particular pattern of organisation or not
Hysteresis
The tendency to remain in the current basin of attraction as the control parameter is increased
Optic Flow
Patterns of apparent motion of objects caused by relative motion of the observer and a scene. It is a phenomenon of direct perception.
