Chapter 6. Touch, Propriocepti

8/4/2019 Chapter 6. Touch, Propriocepti

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Chapter 6

Touch, Proprioception and

VisionConcept: Touch, proprioception and visionare important components of motor control


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Introduction

Sensory information is essential for all theoriesof motor control and learning

Provides pre-movement information

Provides feedback about the movement in progress Provides post-movement information about actiongoal achievement

Focus of current chapter is three types of

sensory information Touch, vision, and proprioception


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Touch and Motor Control

Describe some ways we use touch to helpus achieve action goals

Neural basis of touch [see Fig. 6.1]

Skin receptors

Mechanoreceptors located in the dermis layer ofskin

Greatest concentration in finger tipsProvide CNS with temperature, pain, and

movement info


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Touch and Motor Control, contd

Typical research

technique Compare performanceof task involving finger(s)before and after

anesthetizing finger(s)

Research shows tactile

sensory info influences: Movement accuracy

Movement consistency

Movement force adjustments

Roles of Tactile Info in Motor Control

See an example of research

for typingA Closer Look,

p. 109


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Proprioception and Motor Control

Proprioception:The sensory systemsdetection and reception of movement

and spatial position of limbs, trunk, andhead

We will use the term synonymously with the

term kinesthesis


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Neural Basis of Proprioception

CNS receives proprioception information fromsensory neural pathways that begin inspecialized sensory neurons known as

proprioceptors Located in muscles, tendons, ligaments, and joints

Three primary types of proprioceptors

Muscle spindles Golgi tendon organs

Joint receptors


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Neural Basis of Proprioception:

Proprioceptors

1. Muscle spindles

In most skeletal muscles in a capsule of specializedmuscle fibers and sensory neurons

Intrafusal fibers [see Fig. 6.2] Lie in parallel with extrafusal muscle fibers

Mechanoreceptors that detect changes in muscle fiberlength (i.e. stretch) and velocity (i.e. speed of stretch)

Enables detection of changes in joint angle

Function as a feedback mechanism to CNS to maintainintended limb movement position, direction, and velocity


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Neural Basis of Proprioception:

Proprioceptors, contd

2. Golgi-Tendon Organs(GTO)

In skeletal muscle near

insertion of tendonDetect changes in muscletension (i.e. force)

Poor detectors of musclelength changes

3. Joint Receptors

Several types located injoint capsule and

ligamentsMechanoreceptors thatdetect changes in

Force and rotation appliedto the joint,

Joint movement angle,especially at the extremelimits of angular movementor joint positions


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Techniques to Investigate the Roleof Propioception in Motor Control

Deafferentation techniques

Surgical deafferentation Afferent neutral pathways associated with movements of interest

have been surgically removed or alteredDeafferentation due to sensory neuropathy Sometimes called peripheral neuropathy

Large myelinated fibers of the limb are lost, leading to a loss ofall sensory information except pain and temperature

Temporary deafferentation Nerve block technique Inflate blood-pressure cuff to createtemporary disuse of sensory nerves


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Techniques to Investigate the Role ofPropioception in Motor Control, contd

Tendon vibration technique

Involves high speed vibration of the tendon of

the agonist muscle Proprioceptive feedback is distorted ratherthan removed


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Role of ProprioceptiveFeedback in Motor Control

Research using the deafferentation and tendon vibrationtechniques has demonstrated that proprioceptioninfluences:Movement accuracy

Target accuracy

Spatial and temporal accuracy for movement in progress

Timing of onset of motor commands

Coordination of body and/or limb segments

Postural control Spatial-temporal coupling between limbs and limb segments

Adapting to new situations requiring non-preferred movementcoordination patterns


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Vision and Motor Control

Vision is our preferred source of sensoryinformation

Evidence from everyday experiences Beginning typists look at their fingers

Beginning dancers look at their feet

Evidence from research

The classic moving room experiment


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The Moving Room Experiment

Lee & Aronson (1974)

Participants stood in a room inwhich the walls moved toward

or away from them but floor didnot move

Situation created a conflictbetween which two sensory

systems? Vision & proprioception

Results When the walls moved,

people adjusted theirposture to not fall, eventhough they werentmoving off balance

WHY?


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Neurophysiology of Vision

Basic Anatomy of the Eye

See Figure 6.6 for the following anatomicalcomponents

Cornea Iris

Lens

Sclera

Aqueous humor

Vitreous humor


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Neurophysiology of Vision,contdNeural Components of the Eye and Vision

Retina [see Fig. 6.6]

Fovea centralis

Optic disk

Rods

Cones

Optic nerve (cranial nerve II) [Fig. 6.7]

From the retina to the brains visual cortex


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Techniques for Invesigating the

Role of Vision in Motor Control

Eye movment recording

Tracks foveal visions point of gaze

i.e. what the person is looking at

Temporal occlusion techniques Stop video or film at various times

Spectacles with liquid crystal lenses

Event occlusion technique

Mask view on video or film of specific events orcharacteristics


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Role of Vision in Motor Control

Evidence comes from research investigatingspecific issues and vision characteristics:

1. Monocular vs. Binocular Vision

Binocular vision important for depth-perceptionwhen 3-dimensional features involved inperformance situation, e.g.

Reaching grasping objects

Walking on a cluttered pathway

Intercepting a moving object


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Role of Vision in Motor Control,contd.

2. Central and Peripheral Vision

Central vision

Sometimes called foveal vision

Middle 2-5 deg. of visual field

Provides specific information to allow us to achieveaction goals, e.g.

For reaching and grasping an object specific characteristic

info, e.g. size, shape, required to prepare, move, and graspobject

For walking on a pathway specific pathway info needed tostay on the pathway


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2. Central and Peripheral Vision, contd.

Peripheral vision

Detects info beyond the central vision limits

Upper limit typically ~ 200 deg.

Provides info about the environmental context andthe moving limb(s)

When we move through an environment, peripheralvision detects info by assessing optical flow patterns

Optical flow = rays of light that strike the retina


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2. Central and Peripheral Vision, contd

Two visual systems

Vision for perception (central vision)

Anatomically referred to as the ventral streamfrom visualcortex to temporal lobe

For fine analysis of a scene, e.g. form, features

Typically available to consciousness

Vision for action (peripheral vision)

Anatomically referred to as the dorsal streamfrom visualcortex to posterior parietal lobe

For detecting spatial characteristics of a scene and guidingmovement

Typically not available to consciousness


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3. Perception Action Coupling

As discussed in ch. 5, refers to the coupling

(i.e. linking together) of a perceptual event and

an actionExample of research evidence:

See experiments by Helsen et al. (1998 & 2000)described in textbook (pp.127 128)

Results show that spatial and temporalcharacteristics of limb movements occurred togetherwith specific spatial and temporal characteristics of eyemovements


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4. Amount of Time Needed for MovementCorrections?

Concerns visions feedback role during movement

Researchers have tried to answer this question sinceoriginal work by Woodworth in 1899

Typical procedure: Compare accuracy of rapid manualaiming movements of various MTs with target visible andthen not visible just after movement begins Expect accurate movement with lights off when no visualfeedback needed during movement

Currently, best estimate is a range of 100 160 msec. (Thetypical range for simple RT to a visual signal)


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5. Time-to-Contact: The Optical Variable tauConcerns situations in which Object moving to person must be intercept Person moving toward object needs to contact or avoid contact

with objectVision provides info about time-to-contact object whichmotor control system uses to initiate movement Automatic, non-conscious specification based on changing sizeof object on retina

At critical size, requisite movement initiated

David Lee (1974) showed the time-to-contact infospecified by an optical variable (tau), which could bemathematically quantifiedMotor control benefit Automatic movement initiation

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Chapter 6. Touch, Propriocepti