Neural Mechanisms: Contributions And Control

Chapter 4

Nervous System

Movement prep, execution, and control occur here

CNS vs. PNS

– CNS - Brain and spinal cord

– PNS - nerves that extend off of the brain and spinal cord; ;link body and CNS

Afferent vs. Efferent (PNS) – Afferent - conducts nerve impulses from sensory receptors to the

CNS

– Efferent - transmits impulses from CNS to limbs, muscles, etc.

Sensory Receptors: Stimuli Detection

Exteroceptors: located at or near surface of body

– Detect stimuli outside the body – Provide information about the environment: What’s

happening? Do I feel pain? Interoceptors: hunger

– Detect stimuli from the internal viscera – Provide information about the internal environment

Proprioceptors– Provide information regarding body position and

movement: muscle tension, joint position

Vision

Dominant sensory system

– 70% of sensory receptors are in the eyes

Information from other sensory receptors may be ignored in favor of visual information

Two Visual Systems in Motor Control

Visual information is delivered from the retina along two separate pathways to two different places– Focal vision, specialized for object identification– Ambient vision, specialized for movement control

Although separate, these systems function in parallel

Focal Vision

Functions to identify objects primarily located in the central region of the visual field

– Answers the question “What is it?”

Voluntary; strongly linked to consciousness

Function hampered in low light conditions

Ambient Vision

Involves both the central and peripheral visual fields

Not affected by changes in light strength

Provides information about our own movements in relation to other objects

– Answers questions “Where is it”; “Where am I in relation to it?”

Often functions at subconscious level

– Fine motor control may occur without us knowing it

Parallel Processing

Ambient vision processes the broader environment

Focal vision processes the environment immediately in front

Comparison of the two systems

Feature Focal Vision Ambient Vision

Visual Field Location

Central Only Central and Peripheral

Awareness Conscious Subconscious

Effect of low Illumination

Degradation Very Little

General Question Resolved

What is it? Where is it?

Focal Vision and Movement Control

Since focal vision is at the conscious level, visual information is processed through the information processing stages

Vision is a source of exteroceptive information about the environment

Movement control only occurs as information is processed through the stages

– Focal vision helps one accurately ID a pencil from a pen– Is it as easy to make the ID in low light situations?

Ambient Vision and Movement Control

The flow of light and changes in that flow across the retina provide a person with the following information about their movement

– Stability and balance– Velocity of the movement through the environment– Direction of movement relative to the position of fixed objects

in the environment– Movement of environmental objects relative to the person– Time until contact between the person and an object in the

environment

Time to Contact

As an object approaches the size of the object will increase in the retinal image

Faster the enlargement, the faster the object is approaching– Used to determine when an action should be

initiated

– Ambient vision is used to detect last moment changes

Ambient Vision and Movement Control

Because ambient information functions at the subconscious level, it is relatively fast

– However this information is sent to lower levels of the CNS Not at the same level as where the CNS selects and initiates

movement

– Therefore, ambient vision operates to make minor adjustments to already programmed actions

Ie. Compensate for a head movement when getting ready to swing a golf club or a change in posture when walking with crutches

Vision and Performance

The performer must be able to make quick and accurate decisions with focal vision

The performer must also be able to anticipate someone else’s movement or their own in relation to an object or a person through ambient vision

– Anticipation helps to decrease the information processing time

Visual search strategies will assist in the development of this ability

Visual Search Strategies

Directs learner to information rich areas where critical cues occur

Provide extensive practice opportunities in situations that contain common task relevant cues

Later in development/experience: Design situations with high variability while still requiring the learner to search for same cues each attempt

– Helps prepare learner to generalize visual search strategies for performance or game situations

Visual Dominance

Vision exerts a strong influence on motor control, but it may not always be positive– One may need to use other modes on control

For example, monitor the sound of the engine rather than rely only on gauges in the car

– Over-reliance on vision may create ineffective performance The firefighter who only notices the flames in front and fails to listen to the

cracking of timber to the right or left may be injured

Practical Application

Visual Dominance– Trace between the lines looking through the mirror. – Describe how you performed. What difficulties did you

experience? What conflicts existed between your visual information and your proprioceptor information?

– Describe the link between visual and proprioceptive feedback in the execution of visuomotor tasks.

– Based on your findings, summarize different ways you might help learners in your content field learn to link visual and proprioceptive feedback.

– Turn in your results at our next class.

Proprioceptor Information

Golgi tendon organs; protects tendons & muscles from excessive tension

Muscle spindles;tells CNS how much and how fast a muscle is changing length

Joint kinesthetic receptors; info about movements being too slow, fast or in the wrong direction

Vestibular apparatus; info about posture and balance

Proprioception & motor control

Proprioceptors send info on initial conditions & limb position to the generalized motor program (recall schema)

Proprioceptors evaluate for correctness to the intended goal (recognition schema)

How does this information supplement the focal and ambient vision information?

Implications for learning how to interpret proprioceptive information

Help beginners develop their frame of reference about a movement (How does it feel?; How should it feel?)– Explore various possibilities to begin to develop their

reference– Gain information through proprioceptors as well as

vision– Manual assistance with cues

What do you think?

A middle-aged man wants to learn to rope jump for fitness. Unfortunately, he is visually impaired having lost most sight in a work-related accident. Explain how the man would control the movement. Then describe how you would assist the man in achieving the goal. Discuss some things you might do to encourage the use of other sensory information. Provide supporting rationale for your suggestions.

CNS and Memory

Processes required to plan movement in some way are stored in the CNS

Use of perception, making decisions on movement response and production often come from some type of information that is stored from previous experiences

Storage of information from previous attempts is in memory

Memory

Ability to store and recall information         

 

WORKING MEMORY

Refers to short-term Working memory serves as interactive workspace

– Duration Use information or lose it Hold information for only 20-30 seconds

– Capacity Seven +/- 2 items Increased size of item depends on chunking

WORKING MEMORY

Processing ActivitiesUse information to solve a specific movement

problemUse information to perform the goal of movementUse information in preparing the information for

storage

LONG-TERM MEMORY

Permanent storage of information Duration of information storage is permanent Forgetting occurs when we cannot find a

memory, or it is a retrieval problem Capacity of information storage is unlimited

Subsystems of Long-term Memory

Episodic memory – Contains information about personal experiences

and events that are associated with a specific time and context

Semantic memory – Represents general knowledge that is developed by

our experiences but is not associated with time Procedural memory

– Retains information regarding how to do something– The memory of skills, operations and actions

Relating LTM to motor control

Episodic memory retrieves information– Used as a guidance for what to do from past

experiences

Semantic memory relays what you have learned to do previously (concepts)

Procedural memory puts the plan into motion (blueprint)

GMP provides the ‘blueprint’

Motor program and schema are in procedural memory

In a specific situation, episodic & semantic systems help to determine ‘what to do’

Information interacts with info in procedural memory Motor program is selected with parameters Skill is executed

Forgetting

Decay theory

Interference theory

– Proactive interference

– Retroactive interference

CAUSES OF FORGETTING

Trace decay—time is a factor in working memory Proactive interference—activities that occur prior

to the presentation of information that is to be remembered

Retroactive interference—interfering activity occurs during retention

Forgetting—this is greatest when there is similarity between what is remembered and the interfering activity

Proactive Interference in working memory

NewInfo Recall

Time

Info not to be recalled

Why does proactive interference impact forgetting?

Confusion Similarity of movements mixes up the encoding

of information Ways to decrease impact

– Active rehearsal (talk to yourself, visualization)

Retroactive interference and working memory

Information to be

rememberedRecall

Time

Info not to be remembered

Why does retroactive interference impact forgetting?

Too much similarity between the goal movement and other interfering activity

Perhaps the number of movements to be made or observed during retention interval exceeds attention capacity

Ways to decrease impact– When giving info, avoid showing improper techniques after

proper technique until practice has occurred

FORGETTING AND LONG-TERM MEMORY

Working memory ‘forgets’ more than long-term memory

Certain types of motor skills are remembered more– Continuous versus serial discrete skills (more cognitive

processing or procedural knowledge)– Procedural skills deteriorate over time (use it or lose it)

Long-term memory forgetting may be due to misplacing information or a retrieval problem

STRATEGIES THAT ENHANCE MEMORY PERFORMANCE

Increase the movement’s meaningfulness – Imagery (powerful rehearsal strategy)– Verbal labeling; critical element cue, ‘elbows in’

Inform one about information to be tested (intention to remember)

Group or organize information into ways that are meaningful (subjective organization) – Skilled person seems to organize information as result of

practice; “chunks remembered”

STRATEGIES THAT ENHANCE MEMORY PERFORMANCE

If the context of practice and test are similar, memory is enhanced

This relationship between practice and test context is called the encoding specificity principle– Important that practice conditions are similar to how

skills will be used in game or real life

Practical Application

Generate a list of tips that practitioners could use to help a learner to ‘remember’.