MOTOR: Exam I

Question 0

Fitts and Posner

• • Cognitive stage
• • Associative stage
• • Autonomous stage

Answer 0

Cognitive
– Thinking about learning
– Experimenting with strategies
= Most basic stage of motor skill acquisition

Associative

• • Refining selected strategy
• • Skill develops and improves with practice

Autonomous
– Automaticity of skill
– Attention diverted to scanning environment or multi-tasking
= Expert stage

NOTE: Not truly autonomous if performance declines when distracted

• • May still be highly skilled/”expert”, but not totally automatic
• • Truly “perfect” performance is rare; usually some error due to distraction

Question 1

Theories of Motor Learning and Performance

• • Fitts and Posner
• • Newell
• • Schmidt and Lee
• • Gentile

NOTE: Basic elements

Answer 1

Fitts and Posner

• • Cognitive stage = thinking
• • Associative stage = refining
• • Autonomous stage = automaticity

Newell

• • Novice stage = basic patterns
• • Advanced stage = coordination
• • Expert stage = controlled

Schmidt and Lee

• • Short-term, implicit memory
• • Schema: Recall, Recognition

Gentile

• • Closed to open skills
• • Demands of environment
  • • Context vs. Regulatory Variability
• • Requirements of action
  • • Object manipulation
  • • Body transport

Question 2

Newell

• • Novice stage
• • Advanced stage
• • Expert stage

Answer 2

Novice

• • Understanding basic patterns of movement
• • Few degrees of freedom
• • Highly variable movements trial to trial

Advanced

• • Coordination
• • Increasing degrees of freedom
• • Adds cognitive element
• • Increasing consistency of movement

Expert

• • Controlled
• • Modifying movement to perform desired task (as needed)
• • Variability is a sign of skill
  • • Consistent outcome, but pattern of movement may vary
  • • Ability to adapt to changes in environment

NOTE: Difference in variability between novice and expert

• • Novice variability in outcome
• • Expert variability in pattern to achieve outcome

Question 3

Schmidt and Lee

• • Development of schema
• • Components of schema

Answer 3

Schema = set of rules for performing a movement

Development of schema: All add to our memory of movement
– Short-term, implicit memory of movement components
– Initial movement conditions (e.g., body position, object weight)
– Motor program parameters = patterns of muscle activity
– Knowledge of results (KR) = outcomes or goals of movement
NOTE: Need to decide what error range is acceptable for successful outcome
– Goal of training is to narrow range, but experiencing error critical to learning
– Even experts never perform same task same way every time
– Sensory consequences = experience or perception of movement
– Feedback from multiple sensory systems (e.g., sight, feel, sound)

Components of schema:
– Recall = Set of rules for movement under different conditions
– Common elements of action and organization (i.e., temporal, rhythmic)
– Memory of movement in different environments/conditions
– Expert has ability to adapt to ensure successful outcome
– Recognition
= Rules of movement coupled w/ current conditions
&raquo_space; Expected outcome
– Expert element of schema
– Recognizing what to do under different conditions

Question 4

Gentile

• • Two-dimensional classification system
  • • Demands of environment
    • • Regulatory variability
    • • Context variability
  • • Requirements of action
• • Closed skill
• • Open skill

Answer 4

Two-dimensional classification system:
= Matrix combining demands of environment X requirements of action
– Spectrum of complexity from closed to open skills

– Demands of environment:
– Regulatory variability = stability of environment
Ex: Moving escalator vs. stairs
– Context variability = persons movement in environment
Ex: Standing still vs. balancing on opposite legs
– Progression: Low to high complexity
– Neither RV nor CV
&raquo_space; Only CV&raquo_space; Only RV
&raquo_space; Both RV and CV
– Requirements of action:
– Progression: Low to high complexity
– Neither body movement nor object manipulation
&raquo_space; Only object manipulation&raquo_space; Only body movement
&raquo_space; Both object manipulation and body movement

Closed skill = Performed in stable and predictable environment
Open skill = Performed in unstable and unpredictable environment
– Must use perception and decision-making to adjust movement

NOTE: Most skills somewhere between totally open or closed

Question 5

Definition of terms:

• • Motor learning
• • Motor performance
• • Motor control

Answer 5

Motor learning = acquiring skilled movement as result of practice
= Internal process that determines capability
– Practice = process of squiring skilled movement via repetition
– Characteristics:
– Improves with practice and experience
– Assessed by observing performance for several trials
– Stable under varied circumstances (repeated trials)

Motor performance = observable action or skill

• • Fluctuates day-to-day and trial-to-trial
• • Characteristics:
  • • Influenced by:
    • • Fatigue, pain, and conditioning
    • • Motivation
    • • Attention (distraction)
    • • Physical conditions
    • • Environment

Motor control = study of neural, physical, and behavioral aspects of movement

• • How our brains and bodies and behaviors relate to this movement
• • How we control the movement skill: brain, muscles, and behaviors

Question 6

Types of skill:

• • Motor skill
• • Cognitive skill
• • Discrete skill
• • Serial skill
• • Continuous skill

Answer 6

Motor skill = success determined by quality of movement
– Knowing “how” to do the movement
– Emphasis placed on correct performance
– Decision making is minimized and motor performance is maximized
Cognitive skill = having a strategy for movement
– Knowing “what” to do
– Movement less important than decision guiding movement
– Decision making is maximized and motor performance is minimized

NOTE: Most skills are a combo of motor and cognition
– Usually new skills require more cognition than more proficient skills

Discrete skill = distinct beginning and end
Serial skill = discrete actions linked together
Continuous skill = no distinct beginning and end

Question 7

Feedback:

• • Intrinsic
• • Extrinsic or Augmented
• • Knowledge of Performance (KP)
• • Knowledge of Results (KR)

Answer 7

Intrinsic = info about movement from sensory systems
– Can be confusing since we get input from many systems
Extrinsic = supplemental info from command or cue
NOTE: Manual and verbal cueing would be both intrinsic and extrinsic

KP = info about movement or movement pattern used to achieve outcome
– Compared to intended movement
KR = info about outcome of movement
– Compared to intended outcome

Question 8

Practice:

• • Massed
• • Distributed
• • Constant
• • Variable
• • Whole
• • Part
• • Guidance
• • Discovery
• • Random
• • Blocked
• • Transfer of practice
• • Mental practice

Answer 8

NOTE: Easier&raquo_space; Harder

Massed = time in trial > interval time
Distributed = time in trial < interval time
– More difficult with longer interval between trials (requires recall)

Constant = static or stable conditions for practice
Variable = differing conditions for practice
– Changing surfaces, external environment, etc.

Part = break task into components or interim steps 
Whole = practice entire task as is

Guidance = physical or verbal instructions through task
Discovery = trial and error
– Discovery can be frustrating, unsafe, time-consuming
– Try to become more efficient in discovery

Blocked = practice one task for period of time, then move to other
Random = practice different tasks in random order

Transfer = better transfer between similar skills/movements
Mental = thinking about task (w/o doing) may improve performance

Question 9

Recovery of function

• • Compensation
• • Spared function
• • Stages of recovery
• • Factors affecting recovery

Answer 9

Recovery = regaining motor skill
Compensation = learning new way to achieve same outcome
Spared function = some ability remaining that can be used

Stages:

• • Spontaneous = suddenly able to perform skill
• • Forced = prolonged process of recovery

Factors:

• • Age
• • Injury or lesion (type, extent, location)
• • Pre-injury motor skills (e.g., child still developing)
• • Post-injury factors (e.g., PT, meds, tissue healing)

Question 10

Problem-Based Approach

• • Who?
• • What? Why?
• • Where?

Answer 10

= Key to learning is ability to ask right questions:

Who = characteristics of learner

• • Abilities
• • Experience
• • Motivation

What/Why = goal of task

Where = target context

• • Environment task will take place
• • Attempt to make practice setting as close to actual

Question 11

Levels of sensory input

• • Interoception
• • Exteroception

Answer 11

Interoception = internal sensory feedback

• • Information from inside the body
• • Hunger, fullness, thirst, and pain

Exteroception = sensory feedback from outside body (external environment)
– Vision = dominant source
– Hearing = “audio flow” indicates location, direction, and directs attention
– Olfaction = may trigger movements or reactions
– Proprioception
= Info about body’s position and orientation in space
– From vestibular system, muscle, joints, and cutaneous receptors
– Vestibular = orientation of head relative to gravity
– Other receptors = location of body parts in space
Kinesthesia = Info about limb movements and muscle contractions

Question 12

Proprioceptive sensory mechanisms

• • Muscle spindle
• • GTO
• • Joint receptors
• • Cutaneous receptors

Answer 12

Muscle spindle:
– Located within skeletal muscle fibers (extrafusal)
– Detects muscle lengthening
– Rapid length change&raquo_space; Stretch reflex = Muscle contracts
– Slow length change&raquo_space; No reflex
– Afferent fibers carry signal to spinal cord
– Motor neurons signal spindle fibers to reset length (intrafusal)
&raquo_space; Remains sensitive to length changes

GTO: Golgi Tendon Organ

• • Located in musculotendinous junction
• • Detects changes in muscle tension (force generation)
• • Inhibits muscle force (damps) to protect muscle and tendon

Joint receptors:

• • Free nerve endings
• • Pacinian corpuscles
• • Ruffini endings
• • Golgi type endings

Cutaneous receptors:

• • Free nerve endings
• • Pacinian corpuscles
• • Ruffini endings
• • Meisners corpuscles
• • Merkels discs

Question 13

Joint receptors:

• • Free nerve endings
• • Pacinian corpuscles
• • Ruffini endings
• • Golgi type endings

Cutaneous receptors:

• • Free nerve endings
• • Pacinian corpuscles
• • Ruffini endings
• • Meisners corpuscles
• • Merkels discs
• • Krauses end bulbs
• • Hair follicle receptors

Answer 13

Joint receptors:

• • Free nerve endings = pain and non painful stimuli, biochemical stimuli
  • • Ligaments, synovium, fat pad, joint capsule
• • Pacinian corpuscles = vibration (high freq.), acceleration, high vel. change in joint position
  • • Fibrous layer of joint capsule
• • Ruffini endings = vibration (low freq.), amplitude, stretch of capsule
  • • Fibrous layer of joint capsule
• • Golgi type endings = compression of capsule, tension, stretch of ligaments
  • • Ligaments, joint capsule

NOTE: All provide info to central processes, but none are conscious except pain

Cutaneous receptors:

• • Free nerve endings = pain and non painful stimuli, biochemical stimuli, temp
• • Pacinian corpuscles = vibration (high freq.), pressure (deep touch)
  • • Located in dermis (deeper), resets itself
• • Ruffini endings = vibration (low freq.), stretch of skin
• • Meisners corpuscles = light touch (not sustained), vibration (freq. < 50Hz), speed of stimuli
• • Merkels discs = light touch (sustained, very sensitive)
• • Krauses end bulbs = touch, pressure
• • Hair follicle receptors = movement of hairs on skin

NOTE: Incredibly rich, sensitive, and important source of info
– Respond to chemical, thermal, and inflammatory stimuli

Question 14

Sensory pathways

• • Spinothalamic pathway
• • Spinoreticular pathway
• • Dorsal column pathway

Answer 14

Spinothalamic = pain and temperature
– Dorsal root > Dorsal horn (synapse 1)
> Cross in anterior cord > Ascend in anterolateral tract
> Thalamus (synapse 2) > Sensory cortex

Spinoreticular = pain
– Dorsal root > Dorsal horn (synapse 1)
> Cross in anterior cord > Ascend in anterolateral tract
> Reticular activating area (multiple synapse)
> Sensory cortex (multiple areas)

Dorsal column = touch, pressure, vibration, and proprioception
– Dorsal root > Ascend in dorsal column
> Cuneate or gracile nucleus (synapse 1)
> Cross in anterior medulla
> Thalamus (synapse 2) > Sensory

Question 15

Visual system:

• • Focal vision
• • Ambient vision
• • Visual dominance
• • Visual capture

– Optical flow

Answer 15

Focal vision = identifies objects in center of visual field
– Conscious and affected by light (center of retina = fovea centralis)
– “What is it?”
– Slow, exteroceptive loop (via cerebellum to info processing) = conscious
Ambient vision = detects orientation of body in environment
– Non-conscious and peripheral (light moves across retina)
– Used a lot in movement control
– “Where am I?” or “Where is it?”
– Fast, inner loop (output to motor program) = nonconscious

Visual dominance = visual info dominates info from other senses
– Primary source of sensory input
Visual capture = visual info captures attention more easily than other sources of info

Optical flow = detects patterns of light moving across retina (ambient vision)
– Perceives:
– Motion
– Direction (left or right, towards or away)
– Velocity (across, towards, or away)
– Position
– Stability
– Size of object
NOTE: Perception of movement can be confusing (you moving in environment vs. environment moving around you); optical flow perceives movement of environment, vestibular system helps you determine if visual info is real (vs. you are moving)

Question 16

Compensations for muscle movements

• • Mechanical
• • M1
• • M2
• • Triggered response
• • M3

Answer 16

Compensations = corrections for error in movement

Mechanical = tissue stiffness helps stabilize
M1 = monosynaptic reflex
– Latency = 30-50 ms
– Very rapid, unconscious, limited muscles
– Inflexible, little environmental impact
– No adaptability, effect of instructions or effect of alternatives
M2 = polysynaptic reflex
– Latency = 50-80 ms
– Longer pathway, still unconscious
– Not voluntary, but can be modified/inhibited consciously (involves higher brain centers)
– Low adaptability, effect of instructions or effect of alternatives
Triggered response = rapid, learned, well-practiced response
– Latency = 80-120
– “Wineglass effect”, subcortical but conscious, cutaneous receptors
– Moderate adaptability, effect of instructions or alternatives
M3 = voluntary reaction
– Latency = 120-180 ms
– Much longer pathway (> sensory cortex > motor cortex > muscles)
– Very large adaptability, effect of instructions or alternatives
– Influenced by instruction, anticipation, and stimulus responses
NOTE: Any additional demands on attention will slow reaction time even further

Question 17

Closed-Loop Control System

• • Characteristics
• • Components

Open-Loop Control System

• • Characteristics
• • Components

Answer 17

Closed-Loop = Ongoing modification of movement using peripheral feedback

• • Uses feedback, error detection, and correction processes during movement
• • Slow, deliberate movements (Requires sensory input to guide movement)
• • > 200 ms (M3 voluntary reaction time): Corrections occur a few 100 ms after error
• • Effective in unpredictable and unstable environments
• • Components:
  • • Input = Environment or desired action
  • • Executive = Determines actions (motor planning areas of brain)
  • • Comparator = Error detection (cerebellum)
    • • Compares efferent copy of motor plan from brain w/ sensory feedback
  • • Effector = Carries out movement (spinal cord, motor tracts, muscles)
  • • Output = Outcome of action
  • • Feedback = Info about current state (sensory receptors, afferent pathways)

Open-Loop = Rapid, automatic movements w/ no correction during movement
– Response selection and programming occur before movement (preplanning)
– Triggered as a whole; No error detection or sensory input during movement (too quick)
– < 200 ms (only reflex corrections M1 and M2)
– Effective in stable and predictable environments
– After movement (subsequent trials): Error signal processed (stimulus ID stage)
&raquo_space; Movement correction chosen (response selection)
&raquo_space; Modifications organized and initiated (response programming)
– Components: Input&raquo_space; Executive&raquo_space; Effector
– NO COMPARATOR
– Output&raquo_space; Feedback only after movement is complete

NOTE: Closed and open loop do not act in isolation

Question 18

Motor Program as Open-Loop System

• • Components
• • Characteristics
  • • Attention
  • • Practice
  • • Learning
  • • Storage

Answer 18

Components
– Input = Stimulus (e.g., ball is thrown) (sensory systems)
– Executive (cortical areas: frontal, parietal, temporal, occipital)
– Stimulus Identification (e.g., see ball thrown)
– Response selection (e.g., decision to swing bat)
– Response programming (e.g., how fast and hard, where to swing)
= Preplanning based on sensory inputs and past experience
– Motion and force predetermined
– Effector
– Motor program = code for movement (premotor/motor areas, basal ganglia)
– Spinal cord (and motor tracts) = signal for movement
– Muscles = perform movement

Characteristics

• • Stages of processing used to develop motor program (executive)
• • Little attention needed for movement once program starts
• • Effect of practice
  • • Program can control longer sequences
  • • Movements become more elaborate
• • Effect of learning
  • • Less time needed for programming
  • • More focus on higher-level cognitive function
• • Stored in long-term memory for use in short-term memory PRN

Question 19

Support for Motor Program Theory:

• • Reaction time
• • Deafferentiation
• • EMG activity

Answer 19

Reaction time:
– Reaction time is longer when followed by more complex movement
= More time needed to organize system
– More elements or more limbs involved
– Example: finger lift followed by simple or complex sequence

– Deafferentiation
= Severing sensory nerves (no sensory input)
– Monkeys still able to perform learned activities (gross motor)
– Indicates sensory feedback not needed for motor program (open loop)
– Example: able to swing from branches but not do fine motor

• • EMG activity
  • • Electrical activity same for muscles when limb movement is blocked
  • • No feedback from limbs (not moving) but program remains in muscles

Question 20

Motor Programs:

• • Attributes
• • Roles

Answer 20

Attributes

• • Specific muscles to perform action
• • Order of muscle activation
  • • Proximal before distal (postural modifications first)
• • Force of contractions
• • Timing and sequencing
• • Duration of contractions

Roles

• • Define and issue commands
  • • Require commands (both for closed and open)
• • Organize DoF of movement
  • • How body will move (sequence, timing, etc.)
• • Make postural adjustments
  • • Proximal muscles first for stability
• • Adapt reflexes for goal
  • • Reflexes used to correct movements

Question 21

Central Pattern Generator

• • Differences with motor program
• • Examples
• • Reflex reversal phenomenon

Answer 21

CPG = Centrally located control mechanism

• • Produces repetitive, genetic movements; Triggered by stimulus (environmental input)
• • Complex reflex reaction, but v. rudimentary motion
• • Stimulation at level of cord, not cortical control needed

Difference with motor program:

• • CPG = Genetically defined (NOT learned)
• • Motor program = Learned activities; Developed w/ practice; Used to control learned activities

Examples:
– Locomotion in animals, Swimming in fish, Chewing in hamsters, Slithering in snakes
NOTE: Some elements of human gait, otherwise too complex for CPG only

Reflex reversal:
= Reflex response differs depending on phase of movement
Example:
– Pressure on dorsum of foot:
– Contact w/ surface (heel strike) = Stance phase&raquo_space; Limb EXT (PF)
– Leaving surface (toe-off) = Swing phase &raquo_space; Limb FLEX (DF)
NOTE: Increase stimulus causes increase motion
– Tactile cue during swing increases FLEX
– Tactile cue during stance increases EXT

Question 22

Generalized motor program

• • Definition
• • Modifications
  • • “Surface features”

Answer 22

= General movement pattern stored in long-term memory
– Defines pattern of movement not specific movement
– Modified for use in specific movements
– Adapted to meet demands of task by selecting different parameters
– Selecting different parameters produces different surface features
NOTE: Solves problem of storage space

Surface features:
= Easily changeable components of movement pattern
– Result from changing parameters/constraints of movement
– Parameters set by demands of task

• • Timing or speed (e.g., throwing fast or slow)
  • • Similar pattern of movement regardless of speed
  • • Change movement time while preserving fundamental timing structure
  • • Same timing and sequence of events that can run at different speeds
• • Amplitude (e.g., writing large or small)
  • • Patterns of acceleration same for large or small movements
  • • Vary amplitude of movement by changing acceleration (force)
  • • Same movement structure just big or small
• • Direction (e.g., throw left or right)
  • • Same movement structure directed high, low, R or L
• • Limb and muscles used (e.g., writing on blackboard vs. check)
  • • Same movement structure w/ different effectors

Question 23

Coordination:

• • Definitions
• • Temporal organization
• • Scientific theories

Answer 23

Coordination
= Behavior w/ two or more DoF in relation to each other
= Organization of different elements of complex body/activity
– Produces effective, skilled activity

Temporal organization
= Timing or rhythms of movement patterns
– Different timing or rhythm increases difficulty
– Easier if beats are the same (even if out of phase)

Theories:
– Motor program concepts
– Discrete tasks of short duration (only open loop)
– Preplanning is critical, feedback is not
– Examples: flipping switch, swinging bat
– Self-organizing systems
= Movement pattern or rhythm dominates, regardless of intent
– Continuous, rhythmical tasks of long duration (closed and open loop)
– Examples: swimming, running, driving, walking

Question 24

Reach-and-grasp - - Type of task - - Components - - Effects of: - - Moving block farther away - - Moving arm faster - - Closing eyes - - Adding second limb - - Adding limb w/ different movement

Answer 24

= Discrete, mostly open-loop -- Components -- Transport: Ballistic arm movement (temporal process) -- Grip-formation: Prepares hand to capture object -- Hand opens prematurely, Refines movement as it approaches object -- Widest grip at peak deceleration of arm (Spatial process) NOTE: Temporal component coordinates movement -- Relative timing does not change despite speed or size of object - - Effects of: - - Moving block farther away - - Arm movement changes (has to go farther) - - Hand movement stays same (grip formation same) = Widest at peak deceleration - - Moving arm faster or closing eyes = Hand opens wider - - Compensates for anticipated error (increased spatial variability) - - Still widest at peak deceleration - - Adding second limb - - Difference distances - - Temporal measures same for both arms = Widest grip and grab objects at same time - - Slower than unilateral (More to preplan and more to coordinate) - - Closer limb slows down to match farther limb movement - - Adding second limb w/ complex movement - - Grasp object at same time - - Arm w/ simple movement slows or slightly mirrors complex movement - - Hard to temporally dissociate two arms (Pattern of complex mvmt detected in mvmt of other arm)

Question 25

Human gait: Walking and running - - Type of task - - Triggers for shift from walk to run

Answer 25

Type of task: - - Continuous, self-organizing - - Two generalized motor programs (walk vs. run) Triggers: -- Energy = Inefficiency in metabolic costs -- May be primary catalyst for transition -- Stability = Instability causes transition -- Increasing speed while walking COM shifts forward -- Limbs dissociate >> Transition to run -- Vision = Gait speed increases when perceived speed increases NOTE: Most likely transition occurs based on multi-sensory inputs NOTE: Self-selected walking speed most efficient (healthy people) -- Other factors may limit speed in impaired people (e.g., pain, fear)

Question 26

Coordination in Continuous Tasks: - - Timing (in-phase vs. anti-phase) - - Speed (frequency) - - UE w/ LE - - Contralateral vs. Ipsilateral - - Direction of movement Self-organizing basis

Answer 26

Timing: -- In-phase = same time -- Anti-phase = alternating = Same kinematics (forces) and timing regardless Speed: -- As speed increases stability decreases: -- Switch from in-phase to anti-phase = System moves toward greater stability Example: Alternating finger tap -- Switches to in-phase tap at 2.25 Hz UE and LE: -- Easier to coordinate contralateral limbs -- Easier to coordinate movements in same direction Example: PF (extension) and wrist extension w/ palm up Self-organizing = systems moves toward stability -- Switch to in-phase as speed increases -- Easier to switch from anti-phase to in-phase -- Contralateral movements have less error = Continuous actions modified due to decrease in stability -- Phase transition -- Changes basic form of pattern

Question 27

Invariance or invariant features - - Relative timing - - Surface features - - Parameters

Answer 27

Invariance = Constant characteristics of a movement -- Despite changes in surface features -- Relative timing ~ Fundamental timing structure of movement -- Ratios of durations of movement features -- Ex) Rel. contribution of ind. mm same regardless of movement time NOTE: Applies to walking, running, reach and grasp -- Surface features = Easily changeable components of movement -- Modified as a result of changing parameters -- Speed of movement -- Size of action (amplitude) -- Trajectory of movement -- Forces used to produce action -- Parts of limb used for action -- Parameters = Variable inputs to a generalized motor program -- Same as above

Question 28

Spatial accuracy - - Speed-accuracy tradeoff - - Closed vs. open loop - - Fitts Law

Answer 28

``` Spatial accuracy = Measure of variability in movement's endpoint -- Decreases with increases in (1) Movement distance (2) Movement speed (decreased time) ``` Speed-accuracy trade off = Substitution of accuracy for speed or vice versa -- Closed loop: Accuracy is goal -- Time for feedback and correction during task -- Open loop: Speed is goal -- No feedback or correction during task -- Tradeoff applies to both open- and closed loop Fitts Law = Movement time (MT) linearly related to index of difficulty (ID) -- MT = log (2A/W) A = movement amplitude (distance to target) W = target width -- Changing size of target NOTE: Applies to combined open- and closed-loop tasks -- Blend of programmed actions and feedback -- Initial part of movement is open-loop -- Later part involves error detection and correction (200-1000 ms)

Question 29

Violations of Speed-Accuracy Tradeoff - - Timing accuracy - - Forceful movements

Answer 29

Timing accuracy = Measure of variability in movement time -- Target time for task to take place -- End of movement occurs close in time to another event ***Variability INCREASES as MT INCREASES (speed decreased) Force of movement -- Fastest but most forceful movement = less spatial variability -- Inverted V relation between force/MT and spatial error -- Highest force = fastest (shortest MT) -- Slowest and least forceful = lowest variability -- Second slowest at 50% max torque = highest variability -- Reason? Large forces (>70% max torque) have lower force variability -- Force production is more consistent for near maximal force -- Resultant trajectory is consistent spatially NOTe: Limited number of studies, simple linear arm movements

Question 30

Sources of Error in Rapid Movements - - CNS - - Reflexes - - Nerve impulses - - Muscle force

Answer 30

NOTE: Errors can occur at all points in system CNS: -- Noisy or inconsistent central processes -- Converting nerve impulses to muscle contractions -- Movement planning processes (response selection) -- Stimulus identification **Errors in commands for motor program Reflexes: -- Contribute variability to muscle contractions Nerve impulses: -- Errors in efferent and afferent signals despite same input Muscle forces: -- Up to 70% max force force variability increases -- > 70% max force variability levels off and decreases near max -- Multiple mm contribute to single movement -- Error in any or all increases error in resultant movement -- Minimize # mm (degrees of freedom) to decrease error -- Minimize gravity -- Gait train on knees

Question 31

Movement variability: Good or bad? - - Evidence for good - - Evidence for bad

Answer 31

-- Depends on goal of task Good: - - Postural sway in developmentally delayed children < normal children - - Ability to move COM outside BOS allows exploration of environment - - Post-concussion less variability in sophisticated measures of postural sway Bad: - - Dysmetria: - - Finger-to-nose test for cerebellar injury >> Problems with endpoint accuracy - - Gaze instability: - - Overshooting saccades when trying to fix gaze on target

Question 32

Theories of motor control (in brief) - - Reflex theory - - Hierarchical theory - - Motor programming theory - - System theory - - Dynamical action theory - - Ecological theory

Answer 32

-- Reflex theory = All movements (simple or complex) due to reflex response >> Clinical utility: Reflexes influence movement -- Hierarchical theory = Higher level CNS centers control lower levels -- Higher levels inhibit lower level reflexes; brain pathology >> persistent of primitive reflexes -- Motor program theory = Generalized motor programs for movement patterns -- Based on evidence (still used today): -- Still move without sensory input -- Similar patterns among individuals -- Several variations of patterns -- Complex movement from single stimulus >> Clinical utility: Innate and learned programs do exist -- Focus on self-initiated movements, synergies, task and action (not discrete movements) -- Modify old programs for new skill (train new effectors or retrain old effectors) -- Systems theory = internal and external forces on body predict movement >> Clinical utility: Physical properties of body predict movement kinematics -- Dynamical action theory = All movement is self-organized (no influence of CNS) -- Movements arise from demands of task and environment (physical principles, not neural) >> Clinical utility: Manipulate environment to allow movements to self-organize -- Ecological theory ("Perception action") = Perception of environment drives movement -- Emphasizes exploration and adaptability more than consistency in behavior >> Clinical utility: Perception of environment can influence movement kinematics -- Ability may be impaired due to fear despite innate ability