Transcript Chapter 6. Touch, Proprioception and Vision

Chapter 6
Touch, Proprioception and
Vision
Concept: Touch, proprioception and vision
are important components of motor control
Introduction
Sensory information is essential for all theories
of motor control and learning
– Provides pre-movement information
– Provides feedback about the movement in progress
– Provides post-movement information about action
goal achievement
Focus of current chapter is three types of
sensory information
– Touch, vision, and proprioception
Touch and Motor Control
Describe some ways we use touch to help
us achieve action goals
Neural basis of touch [see Fig. 6.1]
– Skin receptors
Mechanoreceptors located in the dermis layer of
skin
Greatest concentration in finger tips
Provide CNS with temperature, pain, and
movement info
Touch and Motor Control, cont’d
Roles of Tactile Info in Motor Control
Typical research
technique
– Compare performance
of task involving finger(s)
before and after
anesthetizing finger(s)
Research shows tactile
sensory info influences:
– Movement accuracy
– Movement consistency
– Movement force adjustments
See an example of research
for typing – A Closer Look,
p. 109
Proprioception and Motor Control
Proprioception: The sensory system’s
detection and reception of movement
and spatial position of limbs, trunk, and
head
– We will use the term synonymously with the
term “kinesthesis”
Neural Basis of Proprioception
CNS receives proprioception information from
sensory neural pathways that begin in
specialized sensory neurons known as
proprioceptors
– Located in muscles, tendons, ligaments, and joints
Three primary types of proprioceptors
– Muscle spindles
– Golgi tendon organs
– Joint receptors
Neural Basis of Proprioception:
Proprioceptors
1. Muscle spindles
In most skeletal muscles in a capsule of specialized
muscle fibers and sensory neurons
– Intrafusal fibers [see Fig. 6.2]
– Lie in parallel with extrafusal muscle fibers
Mechanoreceptors that detect changes in muscle fiber
length (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 maintain
intended limb movement position, direction, and velocity
Neural Basis of Proprioception:
Proprioceptors, cont’d
2. Golgi-Tendon Organs
(GTO)
In skeletal muscle near
insertion of tendon
Detect changes in muscle
tension (i.e. force)
– Poor detectors of muscle
length changes
3. Joint Receptors
Several types located in
joint capsule and
ligaments
Mechanoreceptors that
detect changes in
– Force and rotation applied
to the joint,
– Joint movement angle,
especially at the extreme
limits of angular movement
or joint positions
Techniques to Investigate the Role of
Propioception in Motor Control
Deafferentation techniques
Surgical deafferentation
– Afferent neutral pathways associated with movements of interest
have been surgically removed or altered
Deafferentation due to sensory neuropathy
– Sometimes called “peripheral neuropathy”
– Large myelinated fibers of the limb are lost, leading to a loss of
all sensory information except pain and temperature
Temporary deafferentation
– “Nerve block technique” – Inflate blood-pressure cuff to create
temporary disuse of sensory nerves
Techniques to Investigate the Role of
Propioception in Motor Control, cont’d
Tendon vibration technique
– Involves high speed vibration of the tendon of
the agonist muscle
– Proprioceptive feedback is distorted rather
than removed
Role of Proprioceptive
Feedback in Motor Control
Research using the deafferentation and tendon vibration
techniques has demonstrated that proprioception
influences:
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 movement
coordination patterns
Vision and Motor Control
Vision is our preferred source of sensory
information
Evidence from everyday experiences
– Beginning typists look at their fingers
– Beginning dancers look at their feet
Evidence from research
– The classic “moving room experiment”
The Moving Room Experiment
Lee & Aronson (1974)
Results
 Participants stood in a room in
which the walls moved toward  When the walls moved,
people adjusted their
or away from them but floor did
posture to not fall, even
not move
though they weren’t
 Situation created a conflict
moving off balance
between which two sensory
 WHY?
systems?
 Vision & proprioception
Neurophysiology of Vision
Basic Anatomy of the Eye
See Figure 6.6 for the following anatomical
components
–
–
–
–
–
–
Cornea
Iris
Lens
Sclera
Aqueous humor
Vitreous humor
Neurophysiology of Vision,
cont’d
Neural 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 brain’s visual cortex
Techniques for Invesigating the
Role of Vision in Motor Control
Eye movment recording
– Tracks foveal vision’s “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 or
characteristics
Role of Vision in Motor Control
Evidence comes from research investigating
specific issues and vision characteristics:
1. Monocular vs. Binocular Vision
Binocular vision important for depth-perception
when 3-dimensional features involved in
performance situation, e.g.
– Reaching – grasping objects
– Walking on a cluttered pathway
– Intercepting a moving object
Role of Vision in Motor Control,
cont’d.
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 achieve
action goals, e.g.
For reaching and grasping an object – specific characteristic
info, e.g. size, shape, required to prepare, move, and grasp
object
For walking on a pathway – specific pathway info needed to
stay on the pathway
Role of Vision in Motor Control,
cont’d.
2. Central and Peripheral Vision, cont’d.
Peripheral vision
– Detects info beyond the central vision limits
Upper limit typically ~ 200 deg.
– Provides info about the environmental context and
the moving limb(s)
– When we move through an environment, peripheral
vision detects info by assessing optical flow patterns
Optical flow = rays of light that strike the retina
Role of Vision in Motor Control,
cont’d.
2. Central and Peripheral Vision, cont’d
Two visual systems
– Vision for perception (central vision)
Anatomically referred to as the ventral stream – from visual
cortex 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 stream – from visual
cortex to posterior parietal lobe
For detecting spatial characteristics of a scene and guiding
movement
Typically not available to consciousness
Role of Vision in Motor Control,
cont’d.
3. Perception – Action Coupling
As discussed in ch. 5, refers to the “coupling”
(i.e. linking together) of a perceptual event and
an action
Example of research evidence:
– See experiments by Helsen et al. (1998 & 2000)
described in textbook (pp.127 – 128)
– Results show that spatial and temporal
characteristics of limb movements occurred together
with specific spatial and temporal characteristics of eye
movements
Role of Vision in Motor Control,
cont’d.
4. Amount of Time Needed for Movement
Corrections?
Concerns vision’s feedback role during movement
Researchers have tried to answer this question since
original work by Woodworth in 1899
Typical procedure: Compare accuracy of rapid manual
aiming movements of various MTs with target visible and
then not visible just after movement begins
– Expect accurate movement with lights off when no visual
feedback needed during movement
– Currently, best estimate is a range of 100 – 160 msec. (The
typical range for simple RT to a visual signal)
Role of Vision in Motor Control,
cont’d.
5. Time-to-Contact: The Optical Variable tau
Concerns situations in which
– Object moving to person must be intercept
– Person moving toward object needs to contact or avoid contact
with object
Vision provides info about time-to-contact object which
motor control system uses to initiate movement
– Automatic, non-conscious specification based on changing size
of object on retina
– At critical size, requisite movement initiated
David Lee (1974) showed the time-to-contact info
specified by an optical variable (tau), which could be
mathematically quantified
Motor control benefit – Automatic movement initiation