Chapter 15 Basic concepts of motor control: Cognitive science perspectives

Cognitive science perspectives Objective from syllabus To understand how models of motor control can be used to explain how we move The general notion is that the brain & CNS is rather too complex to fully understand at this time, so we need a level of analysis once removed

Using Models to Study Motor Control The role of models in scientific study Key properties to be explained by models of control Degrees of freedom Motor equivalence Serial order Perceptual-motor integration Skill acquisition (ch. 17)

Information-Processing Models of Motor Control The human motor system as computer-like Hardware (brain, receptors, effectors) and software (computational capabilities of these) Processing stages See next 5 slides for examples (a model, followed by some movements that it might help explain)

Executive (conscious) Executive (unconscious) Central Pattern Generator Movement Conscious intentions Environment Sets up the intended movement, with reference to current body state and environmental cues Signal diversifies, with detail added at this level including necessary communication between muscles systems Collections of motor units innervated, leading to contractions of various strengths Body movement affects environmental goals, and always changes our orientation with respect to the environment Feedback Loops 1. A model Note many levels of control

Executive (conscious) Executive (unconscious) Central Pattern Generator Movement Conscious intentions Environment Sets up the intended movement, with reference to current body state and environmental cues Signal diversifies, with detail added at this level including necessary communication between muscles systems Collections of motor units innervated, leading to contractions of various strengths Body movement affects environmental goals, and always changes our orientation with respect to the environment Feedback Loops 2. A knee-jerk (stretch, myotatic, monosynaptic) reflex So it’s fast, but doesn’t do much in terms of coordination

Executive (conscious) Executive (unconscious) Central Pattern Generator Movement Conscious intentions Environment Sets up the intended movement, with reference to current body state and environmental cues Signal diversifies, with detail added at this level including necessary communication between muscles systems Collections of motor units innervated, leading to contractions of various strengths Body movement affects environmental goals, and always changes our orientation with respect to the environment Feedback Loops 3. Balance (swinging room and normal) Fast, due to lack of conscious mediation, and complex

Executive (conscious) Executive (unconscious) Central Pattern Generator Movement Conscious intentions Environment Sets up the intended movement, with reference to current body state and environmental cues Signal diversifies, with detail added at this level including necessary communication between muscles systems Collections of motor units innervated, leading to contractions of various strengths Body movement affects environmental goals, and always changes our orientation with respect to the environment Feedback Loops 4. Poorly learned skill Conscious deliberation makes performance jerky, stiff, awkward

Executive (conscious) Executive (unconscious) Central Pattern Generator Movement Conscious intentions Environment Sets up the intended movement, with reference to current body state and environmental cues Signal diversifies, with detail added at this level including necessary communication between muscles systems Collections of motor units innervated, leading to contractions of various strengths Body movement affects environmental goals, and always changes our orientation with respect to the environment Feedback Loops 5. Expertly learned skill Lengthy practice “automates” performance – think of tying your shoelaces as an example Used just to get things started – will perhaps monitor for errors, but that’s perhaps not a good thing (self-talk)

An Alternative Model of Motor Control Problems with information processing accounts Homunculi - Infinite regress (why do we walk the way we do?) Context-conditioned variability anatomical (muscles used to produce a given movement change with regard to current body ‘context’) mechanical (action of a fixed degree of contraction of a muscle changes with respect to current body position) Distributed, not central control

An Alternative Model of Motor Control A group of related theories Complex systems theory Dynamic pattern perspective & synergetics Ecological psychology All have in common the tendency to ask why rather than how The study of relationships among things, rather than the things themselves Leads to the study of...

Dynamic Pattern Theory Shaping movement via: Constraints... Things which limit our range of movements – thus “shaping” them...and affordances Things which permit (or even suggest) certain methods of movement or interaction with an object

Dynamic Pattern Theory Surface type Lighting Visual flow Speed/accuracy requirements Number of tasks standing seated moving Sensory loss Cognition Flexibility Strength/power Cardiovascular Environmental Constraints Individual Capabilities Task Demands 3 categories of constraint (+ examples) Motor abilities Environmental stability From Newell (1986)

Dynamic Pattern Theory Processes in coordination dynamics Dynamics of CNS (neural level) Dynamics of action system (effector level) Dynamics of environment (environmental level) ConnectionismAction system theory Laws of perceiving and acting (ecological psychology) Coordination dynamics From Schmidt & Fitzpatrick (1993)

Dynamic Pattern Theory Constraints and affordances lead to pattern formation Remember, this is a theory about shaping of movement Why do we walk the way we do?

Dynamic Pattern Theory An example of emergent patterns from motor development Stepping/Walking 0-2 months Stepping a stable behavior 3-4 months Stepping disappears Why? Where might you look if you believed in constraints and affordances? How might you examine this?

Dynamic Pattern Theory An example of emergent patterns from motor development What causes this loss of stability? How might you regain it? 1 month3 months And how else might you lose it?

Dynamic Pattern Theory See anything that changes? New born 3 months

Dynamic Pattern Theory An example of emergent patterns from motor development What causes this loss of stability? How might you regain it? 1 month3 months And how else might you lose it?

Dynamic Pattern Theory In complex systems terms, there are several aspects to this relationship: Self-organization Attractor Order parameter Control Parameter Stability Energy efficiency Critical fluctuation Critical slowing down Hysteresis

An example from adult movement Kelso & Scholtz, 1985 In-phase: Faster and faster…

An example from adult movement Kelso & Scholtz, 1985 In-phase: Faster and faster… Kelso & Scholtz, 1985

An example from adult movement Kelso & Scholtz, 1985 Anti-phase: Faster and faster… Kelso & Scholtz, 1985

An example from adult movement Kelso & Scholtz, 1985 Anti-phase: Faster and faster… Kelso & Scholtz, 1985

An example from adult movement Difference between jt. Angles CoordinationStability Variation in jt. Angles (arbitrary units) Stability and attractors The in-phase and out-of- phase states in the Kelso example are attractor states for the movement Perturbing the movement when it is in a stable attractor region will result in a quick return to stability (in- phase)

An example from adult movement Stability and attractors Perturbing the movement when it is close to a region of instability will result in either a longer period of instability followed by a resumption of the original state, or a new attractor state When close to a period of transition, the movement will exhibit critical fluctuations the movement will be more ‘wobbly,’ less stable Difference between jt. Angles CoordinationStability Variation in jt. Angles (arbitrary units)

Aspects of dynamic systems Listen to this first! Then proceed with the others, going from 1 to 5 Hysteresis in gait

Aspects of dynamic systems Walk Run Speed (control parameter) Order parameters The difference in the speed (at which the person is running/walking) when the transition is made from walking to running, compared to when the switch is made from running to walking, signifies the presence of hysteresis – further definition in audio Hysteresis in gait

Aspects of dynamic systems As it turns out, much the same relationship exists in many other systems: Other examples of human coordination Human cortical activity Cardiac rhythms Water flowing from a tap Water being heated Horses (& other quadrupeds) changing gait Stock market, weather patterns, emotional fluctuations, etc.