M3 Motor Programs

motor program

pre-structured set of movement commands that defines and shapes movement

• requires executive and effectors

• w/ practice, capable of controlling longer strings of behaviour

  *exclusively covers specific, isolated actions unlike GMPs

executive

responsible for creation of instructions included in motor programs

effector

responsible for carrying out instructions specified by executive

open loop system

type of control system where actions are executed w/o feedback or continuous monitoring

• lack of feedback means modifications to actions cannot be made while action is being executed

characteristics of open loop system

• instructions made in advance

• once program initiated, system executes instructions w/ no to little modification

• no feedback; means no ability to detect/correct errors

• only effective in predictable, stable environments

actions controlled by open loop

rapid, brief actions (such as kicking and pressing a button) are controlled in an open loop fashion

open vs closed loop

if movement is slow or long duration; control dominated by feedback processes

if movement is fast or short-duration; control dominated by open-loop

*most tasks, require a blend of closed and open loop control

programmed action

a movement that is organized in advance, and is triggered as a whole, carried out w/ little modification from sensory feedback

• utilized most by open-loop control

central movement organization

term that describes movement details as being determined by the CNS and sent to the muscles, rather than being controlled by peripheral processes involving feedback

support for MP

many lines of evidence support the motor program theory:

• reaction time/startle reaction time

• Henry and Rogers experiment (1960)

• deafferention

• Wadman et al (1979)

reaction time

refers to the amount of time it takes for a person to respond to a stimulus

slowed when:

• more info needs to be processed (e.g Hick’s Law)

• when processing was not ‘natural’ (e.g S-R incompatible stiuations)

*suggests brain needs more time to retrieve and prepare the motor program when a task is complex

Hick’s Law

as the number of choices increases, the reaction time to select a response increases logarithmically

• essentially, the more choices you have, the longer it takes to decide

S-R incompatible

refers to a condition where the stimulus (S) and the required response (R) are not naturally aligned or intuitively related

• e.g driving on the left side of a road in a foreign country

how RT is measured

RT measured from presentation of the stimulus until the movement begins (the actual time it takes to complete the movement itself does not contribute to RT)

• generally, RT determined by duration of stimulus identification and response selection stages

startle RT

phenomenon where reaction time is shortened due to a completely unexpected event (loud noise, brightlight, etc)

• research unclear as to why this happens

  • some suggest executive is bypassed when this happens

  • others say executive speeds up processing time

*supports the idea that the movement was pre-programmed and ready to be executed

Henry and Rogers (1960)

participants performed the following:

• A simple button press.

• A button press followed by arm movement.

• A button press with arm movement and grasping a ball

found that more complex the action, the longer the RT

• suggests complex motor programs require more preparation time, supporting the idea that movements rely on stored programs

deafferention

surgical technique involving the cutting of one or more afferent nerve bundles that enter the spinal cord

• sensory info not perceived, but motor movements produced are relatively fine

  • sensory info not critical for movement production)

*can still perform previously learned movements with reasonable accuracy suggesting that movements are guided by pre-structured motor programs

Wadman et al (1979)

participants asked to extend arm as fast as possible

• in some trials, arm was physically blocked by mechanical arm

found that electrical signal sent to muscles were the same for both blocked and non-blocked trials (motor plan had already been initiated and executed in its ENTIRETY)

• suggests that brain does not make commands on the fly, specific instructions are sent out and executed as a pre-structured plan

limitations of motor program theory

• novelty problem

• storage problem

novelty problem

motor program theory fails to account for how new movements are produced

storage problem

motor program theory fails to consider the amount of motor programs one would need to store in order to move

• lack of efficiency

motor schema theory

proposed by Richard Schmidt in 1975

• involves the use of generalized motor programs

  • fixes novelty and storage problems

• GMPs are refined over time through schemas, which are sets of rules developed through practice and experience

generalized motor program

motor programs that can be applied flexibly to various movements

• usually covers a “class” of movements which can be adapted to fit a situation

  • e.g movement class “throwing” covers overhand throw, underhand throw, throwing light object, throwing heavy object, etc

GMP features

GMPs have the following features:

• invariant features

• parameters (surface features)

invariant features

core components of a GMP that remain constant across different variations of that movement; includes

• relative timing

• relative force

• sequence (order of events)

parameters

(aka surface features) modifiable aspects of a GMP that can change to fit the specific demands of a task/situation; includes:

• overall duration

• overall force

• movement amplitude

• effectors involved

overall duration

a parameter that refers to the total time required to complete the movement

• e.g a baseball pitcher can throw fast or slow, but sequence and relative timing of the throw remains the same

overall force

(aka intensity) a parameter that refers to total amount of force applied during the movement

• e.g kicking a soccer ball gently vs. powerfully uses the same movement structure, but force differs

movement amplitude

a parameter that refers to the size or range of the movement

• e.g writing a signature on paper vs. on a whiteboard involves the same pattern of hand movements but w/ different amplitudes

effectors involved

a parameter that refers to the amount of muscles or limbs used during a movement

• e.g you can write with your dominant hand, non-dominant hand, or even your foot; GMP remains similar, though the effectors change

James 1891 study

found that the most attention-demanding step is the first step when walking

• suggests when you start a sequence of muscle contractions, the very first contraction requires more attention than the others

  • starts a sequence of muscle contractions that flow w/ each other

Wolpert & Ghahramani (2000)

developed theory on how the brain deals with multiple streams of sensory input (e.g., visual, auditory, proprioceptive, vestibular)

• Bayesian Integration

• redundancy of sensory inputs

Bayesian integration

refers to how each sensory modality contributes to the final estimate of the state (like position or velocity) based on its reliability

• e.g If vision is blurry, the brain relies more on proprioception to estimate hand position. If vision is sharp, it plays a stronger role in the final estimate

redundancy of sensory inputs

our senses (e.g., vision, touch, proprioception) often provide redundant or overlapping information

e.g When you move your hand, both vision and proprioception provide information about the hand’s position