chapter 8: motor control powerpoint by glenn e. meyer, trinity university cognition – 2/e dr....

Chapter 8:Chapter 8:

Motor ControlMotor ControlPowerPoint by Glenn E. Meyer, Trinity UniversityPowerPoint by Glenn E. Meyer, Trinity University

Cognition – 2/eCognition – 2/eDr. Daniel B. WillinghamDr. Daniel B. Willingham

©2004 Prentice Hall©2004 Prentice Hall 22

How Do We Select a Movement?How Do We Select a Movement?

• Efficiency TheoriesEfficiency Theories• Synergy TheoriesSynergy Theories• The Mass Spring ModelThe Mass Spring Model• Which Model is Right?Which Model is Right?


Efficiency Theories Efficiency Theories

• Important Terms:Important Terms: Degrees of Freedom Problem The problem of how the mind selects Degrees of Freedom Problem The problem of how the mind selects

which way to execute a movement, given that there are many ways which way to execute a movement, given that there are many ways to make any given movementto make any given movement

o Trajectory: The path of a movement Trajectory: The path of a movement o Effector: Part of the body that you use to have an effect on the Effector: Part of the body that you use to have an effect on the

environment (e.g., the hand, the foot). environment (e.g., the hand, the foot). • Efficiency Theory:Efficiency Theory:

A solution to the degrees of freedom problem in motor control, which A solution to the degrees of freedom problem in motor control, which claims that movements are evaluated for their efficiency and the most claims that movements are evaluated for their efficiency and the most efficient movement, is selected. efficient movement, is selected. Problem: What is best measure of efficiency?Problem: What is best measure of efficiency?

o Joint space: In motor control, a representation for planning Joint space: In motor control, a representation for planning movements that uses joint angles movements that uses joint angles

o Cartesian SpaceCartesian Spaceo Minimum Joint TorqueMinimum Joint Torqueo Minimizing Jerk: Rate of acceleration. Used as a measure of efficiency Minimizing Jerk: Rate of acceleration. Used as a measure of efficiency

in one theory addressing the degrees of freedom problem in one theory addressing the degrees of freedom problem


Synergy TheoriesSynergy Theories

• SynergySynergyBiases for joints or muscle groups to work Biases for joints or muscle groups to work together in a particular way together in a particular way

• Evidence for:Evidence for: Santello, et al (1998) as seen in Fig. 8.2, argue for two Santello, et al (1998) as seen in Fig. 8.2, argue for two

basic postures and synergies that explain a grasping basic postures and synergies that explain a grasping situationsituation

Anticipatory Postural Adjustment Anticipatory Postural Adjustment Muscle contractions that counteract changes in the Muscle contractions that counteract changes in the center of gravity that occur due to other movements center of gravity that occur due to other movements (e.g., reaching movements) – seen in reaching behavior, (e.g., reaching movements) – seen in reaching behavior, counteracting what makes you unstablecounteracting what makes you unstable


The Mass Spring ModelThe Mass Spring Model• Mass spring model: Mass spring model:

A model addressing the degrees of freedom problem that capitalizes on a A model addressing the degrees of freedom problem that capitalizes on a biomechanical property of the way our muscles and limbs are designed. It biomechanical property of the way our muscles and limbs are designed. It proposes that endpoints are selected for movements, but trajectories are proposes that endpoints are selected for movements, but trajectories are not planned – as seen in Fig 8.3not planned – as seen in Fig 8.3

Evidence: Polit and Bizzi (1978) as seen in Fig. 8.4 , use and non-Evidence: Polit and Bizzi (1978) as seen in Fig. 8.4 , use and non-use of proprioceptive information by monkeyuse of proprioceptive information by monkey

o Proprioception Proprioception A sense of the body’s location generated by any of a number of special A sense of the body’s location generated by any of a number of special receptors in the joints, skin, and muscles receptors in the joints, skin, and muscles

Graziano, et al. (2002) – electrical simulation of motor cortices in Graziano, et al. (2002) – electrical simulation of motor cortices in monkey – stimulated predicted endpointsmonkey – stimulated predicted endpoints

Which Model is Right?Which Model is Right?• Correct model needs to incorporate many of the modelsCorrect model needs to incorporate many of the models• Rosenbaum, et al. (1993, 1995, 2001) combines many factors:Rosenbaum, et al. (1993, 1995, 2001) combines many factors:

Endpoints selectedEndpoints selected Trajectory develops naturally as joint angles go to target postureTrajectory develops naturally as joint angles go to target posture Movement selected by criteria: accuracy and energyMovement selected by criteria: accuracy and energy


How are the Movements Sequenced?How are the Movements Sequenced?

• Response ChainingResponse Chaining• Motor Program TheoriesMotor Program Theories• Hierarchical Control in Motor Hierarchical Control in Motor

ProgramsPrograms


Response ChainingResponse Chaining

• Response chaining Response chaining A theory of how sequences are organized in motor control. A A theory of how sequences are organized in motor control. A movement Glossary triggers a proprioceptive feeling of having movement Glossary triggers a proprioceptive feeling of having completed the movement, which triggers the next movement, and so completed the movement, which triggers the next movement, and so on. on. Suggested by James – based on proprioceptive feedback as seen in Fig. 8.6Suggested by James – based on proprioceptive feedback as seen in Fig. 8.6 Lashley (1951) – argued against as speed of skilled movements argues Lashley (1951) – argued against as speed of skilled movements argues

against use of proprioceptionagainst use of proprioception Experiments severing dorsal roots of spinal cord don’t support the theoryExperiments severing dorsal roots of spinal cord don’t support the theory


Motor Program TheoriesMotor Program Theories

• Motor program Theory (Keele, 1981)Motor program Theory (Keele, 1981) A representation supporting movement that has three A representation supporting movement that has three

key features: key features: o it contains a set of commands for movementit contains a set of commands for movemento peripheral feedback is not neededperipheral feedback is not neededo the commands can be applied to different effectorsthe commands can be applied to different effectors

Supporting evidence – Supporting evidence – o Henry and Dodd (1960) – time it takes to initiate a series of Henry and Dodd (1960) – time it takes to initiate a series of

commands depends on the number of movements in the seriescommands depends on the number of movements in the serieso Taub shows monkeys can produce actions without Taub shows monkeys can produce actions without

propioceptionpropioceptiono You can write your name with the nondominate hand or a foot You can write your name with the nondominate hand or a foot

– as seen in Fig. 8.7– as seen in Fig. 8.7


Hierarchical Control in Motor ProgramsHierarchical Control in Motor Programs

• Motor sequences are organized hierarchically as seen in Motor sequences are organized hierarchically as seen in Fig. 8.8. Hierarchical schemes contain:Fig. 8.8. Hierarchical schemes contain: Movement nodes: In a hierarchical sequencing representation, the Movement nodes: In a hierarchical sequencing representation, the

movement nodes control muscles movement nodes control muscles Control nodes: In a hierarchical sequencing representation, the Control nodes: In a hierarchical sequencing representation, the

control nodes tell the movement nodes what to do. control nodes tell the movement nodes what to do.

• Supporting Evidence:Supporting Evidence: Rosenbaum, et al. (1983) as seen in Fig. 8.9. Time between key Rosenbaum, et al. (1983) as seen in Fig. 8.9. Time between key

presses depends on number of nodes traversedpresses depends on number of nodes traversed MacKay and Bowman (1969) as seen in Table 8.1 – argues for two MacKay and Bowman (1969) as seen in Table 8.1 – argues for two

levels of speech productionlevels of speech productiono Control of articulatorsControl of articulatorso Abstract Control of words to be saidAbstract Control of words to be said


How Is Perceptual Information Integrated How Is Perceptual Information Integrated into Ongoing Moments?into Ongoing Moments?

• VisionVision• PropioceptionPropioception


VisionVision

• Questions:Questions: What is the relation of the visual system’s What is the relation of the visual system’s

“How” system to motor control“How” system to motor control Is visual feedback needed for motor control, as Is visual feedback needed for motor control, as

in reaching?in reaching?o Zelaznik et al. (1983), as in Fig. 8-10, found for Zelaznik et al. (1983), as in Fig. 8-10, found for

fastest movements vision did not contribute but fastest movements vision did not contribute but when movements took when movements took >> 150 ms, feedback made 150 ms, feedback made them more accuratethem more accurate

o Constant visual feedback not needed, periodic Constant visual feedback not needed, periodic feedback can be substituted as seen in Fig. 8-11 feedback can be substituted as seen in Fig. 8-11 (Elliot, et al., 1994)(Elliot, et al., 1994)


Propioception Propioception

• Proprioception :Proprioception :A sense of the body’s location generated by any of a number of special receptors A sense of the body’s location generated by any of a number of special receptors in the joints, skin, and muscles:in the joints, skin, and muscles: Muscle receptors:Muscle receptors:

o Muscle Spindles: Receptors in the fleshy part of muscles that detect muscle stretch. They are Muscle Spindles: Receptors in the fleshy part of muscles that detect muscle stretch. They are important for proprioception important for proprioception

o Golgi Tendon Organs: Receptors located where the muscles and tendons join that are active Golgi Tendon Organs: Receptors located where the muscles and tendons join that are active when muscles stretch. They are important for proprioception when muscles stretch. They are important for proprioception

Cutaneous receptors: Receptors in and under the skin. Some of these respond when the Cutaneous receptors: Receptors in and under the skin. Some of these respond when the skin is displaced by pressure. This is important in detecting the pressure exerted by skin is displaced by pressure. This is important in detecting the pressure exerted by muscle contraction, as when you grip a glass muscle contraction, as when you grip a glass

Joint Receptors: located in joints and fire for extreme joint anglesJoint Receptors: located in joints and fire for extreme joint angles

• Loss of propioception is devastating and vision cannot substitute in some tasks Loss of propioception is devastating and vision cannot substitute in some tasks (Cole, 1995) but can in others (Sanes et al., 1985 as seen in Fig, 8-12)(Cole, 1995) but can in others (Sanes et al., 1985 as seen in Fig, 8-12)

• Propioception contributes Propioception contributes egocentric spatial representationegocentric spatial representation: A spatial : A spatial representation in which objects are located relative to part of the body as seen in representation in which objects are located relative to part of the body as seen in Fig. 8-13Fig. 8-13 Evidence suggest egocentric spatial representation is used to support movement as seen Evidence suggest egocentric spatial representation is used to support movement as seen

in Fig. 8-15 (Blouin, et al., 1993)in Fig. 8-15 (Blouin, et al., 1993)


How Are Motor Skills Learned?How Are Motor Skills Learned?

• Three Obvious Properties of Motor Three Obvious Properties of Motor Skill LearningSkill Learning

• Two Approaches to Motor Skill Two Approaches to Motor Skill LearningLearning


Three Obvious Properties of Motor Skill Learning Three Obvious Properties of Motor Skill Learning

• Motor skill learning Increasing accuracy (either Motor skill learning Increasing accuracy (either spatial or temporal accuracy) of motor acts that spatial or temporal accuracy) of motor acts that occur as a result of practiceoccur as a result of practice

• Three PropertiesThree Properties GeneralizationGeneralization

o Transfer depends not just on overall similarity but on Transfer depends not just on overall similarity but on representation of the skill (Willingham, 1997,1998)representation of the skill (Willingham, 1997,1998)

Long-Term Retention Long-Term Retention o As seen in Fig 8.18 (Fleishman and Parker, 1962)As seen in Fig 8.18 (Fleishman and Parker, 1962)

Automaticity: Automaticity: o When motor skills are practiced to sufficient degree, the When motor skills are practiced to sufficient degree, the

attentional demand for the action is reduced as is the felt need attentional demand for the action is reduced as is the felt need for conscious direction of the action. Consistent feature of well for conscious direction of the action. Consistent feature of well trained skills (Wulf and Prinz, 2001) trained skills (Wulf and Prinz, 2001)


Two Approaches to Motor Skill LearningTwo Approaches to Motor Skill Learning

• Generalized Motor Programs:Generalized Motor Programs: A motor program that can produce not just a specific A motor program that can produce not just a specific

movement, but a whole class of movementsmovement, but a whole class of movements Motor skill learning is matter of acquiring generalized Motor skill learning is matter of acquiring generalized

motor programs – Schmidt’s (1975) schema theorymotor programs – Schmidt’s (1975) schema theory Can be thought of as a function that relates some input Can be thought of as a function that relates some input

parameters to a pattern of movements that will produce parameters to a pattern of movements that will produce a desired outcome as seen in Fig 8.18a desired outcome as seen in Fig 8.18

Ability to generalize will be better if you have trained in Ability to generalize will be better if you have trained in a broader set of circumstancesa broader set of circumstances

• There is ongoing debate about the predictions of There is ongoing debate about the predictions of the theorythe theory


Two Approaches - ContinuedTwo Approaches - Continued

• Multiple Processes - WillinghamMultiple Processes - Willingham Many brain areas involved, suggesting several systemsMany brain areas involved, suggesting several systems Motor skill learning is the adjustment of motor control processes to Motor skill learning is the adjustment of motor control processes to

work more effectively in particular environmentswork more effectively in particular environments Suggested Processes to Support Motor-Skill Learning (as seen in Suggested Processes to Support Motor-Skill Learning (as seen in

Table 8.2)Table 8.2)o Strategic:Strategic:

Selects goal of movement in environment coordinates. Selects goal of movement in environment coordinates. o Perceptual-motor integration:Perceptual-motor integration:

Selects spatial targets for movement that will fulfill environmental goal;Selects spatial targets for movement that will fulfill environmental goal;represented in egocentric space. represented in egocentric space.

o Sequencing: Sequencing: Orders spatial targets in the correct sequencesOrders spatial targets in the correct sequences

o Dynamic: Dynamic: Translates egocentric spatial targets and a pattern of muscle firingTranslates egocentric spatial targets and a pattern of muscle firing

Processes can operate in conscious or unconscious mode, rely on Processes can operate in conscious or unconscious mode, rely on different neural structuresdifferent neural structures

chapter 8: motor control powerpoint by glenn e. meyer, trinity university cognition – 2/e dr....

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