Transcript Dynamic visual acuity

Movement and the
Changing Senses
The communicative link between
the human organism and the
environment is in part made
possible by the senses: vision,
proprioception, touch, taste,
smell, and hearing
• We rely on vision more than any other sense
• Most movement tasks are initiated by visual
information
• Nonvisual modalities also influence motor
development and performance
Understanding the Mechanics of Vision
• Light rays converge and meet at a focal point
– The cornea and the fluids in the eye refract (bend)
the light rays
• The lens can adjust the focal point by
changing shape
– Relaxation of the ciliary muscles causes the lens to
flatten
– Contraction of the ciliary muscles causes the lens
to become more spherical
Understanding the Mechanics of Vision
• Accommodation is the adjustment of the
eye to variations in distance
• The retina contains two photoreceptors
– Rods are responsible for vision in low
illumination (night vision)
– Cones are responsible for color vision and
visual acuity
Understanding the Mechanics of Vision
• Macula: an oval yellow spot at the center
of the retina
• Fovea: (point of best vision) is located
here
• Cone cells are concentrated
• There is an absence of rod cells
Retina
Understanding the Mechanics of Vision
Physical Development of the Eye
• The eye develops as an outgrowth of the
forebrain
– Part of the central nervous system
– 6 cranial nerves govern vision
• At birth
– The eye is hyperopic (light focuses behind
the retina)
– The retina contains mostly rod cells
Physical Development of the Eye
• At 1 month postnatal
– Cone cells appear
• At 8 months postnatal
– Macula is mature
Development of Selected
Visual Traits and Skilled
Motor Performance
Visual Acuity
• Degree of detail that
can be seen in an
object
• A Snellen eye chart
is used to determine
visual acuity
Visual Acuity
• This Snellen eye chart is
used with children in
grades K-1 who may not be
capable of letter recognition
Visual Acuity
• Static visual acuity
– Target and performer are stationary
– 20/20 vision means that you see at 20 ft
what a person with normal vision sees at 20
ft
– 20/100 means that you see at 20 ft what a
person with normal vision sees at 100 ft
Age
Visual Acuity
Birth
20/200 and 20/400
6 months
20/200
1 yr
20/50
4-5 yr
20/20
Visual Acuity
• Dynamic visual acuity
– Ability to see the detail in moving objects
– Ability of the central nervous system to
estimate an object’s direction
– Ability of the ocular-motor system “to catch”
and “to hold” an object’s image on the eye’s
fovea long enough to see detail
Visual Acuity and Motor Performance
• Both static and dynamic visual acuity play
keys roles
• Dynamic visual acuity is highly correlated with
success in
– Field-goal shooting
– Ball catching
Visual Acuity and Exercise
• Aerobic activities appear to improve visual
acuity for up to two hours post-exercise
• Increase in acuity due to increase in blood flow
and oxygenation to the eye
Visual Acuity and Aging
• Age-related eye
• Conditions/diseases
diseases (ARED) are
– Age-related macular
degeneration
the leading cause of
– Glaucoma
loss of visual acuity
–
–
–
–
Cataracts
Senile miosis
Diabetic retinopathy
Presbyopia
AREDs
• Age-related macular
degeneration (AMD)
– Loss of central vision
– Dry form
• Breakdown of light sensitive cells in the
macula
• Not allowed to drive and will have
trouble reading
• No problem with general movement
Normal
Amsler Grid
– Wet form
• New blood vessels form behind the
retina, leak, and destroy the macula
Visual acuity = 20/50-20/100-total blindness
AMD
AREDs
• Glaucoma
– Leading cause of loss in visual acuity and
blindness
– Circulating fluids of eye are blocked
resulting in high pressure in eye
– Loss of peripheral vision
– Eventual loss of central vision
Age-Related Eye
Diseases
AREDs
• Cataracts
– Clouding of the eye’s lens
– Initial symptoms include complaints of glare,
colors that seem faded, and increased need
for light when reading
– Smoking, alcohol, and sun’s UV exposure
increase the risk for developing cataracts
AREDs
• Senile miosis
– Normal loss of light restriction to the eye
with age
– Decrease in resting diameter of the pupil
– Linear decline in the amount of light
reaching the retina between 30-60 years
AREDs
• Diabetic retinopathy
– Complication of diabetes
– Vessels in the retina may hemorrhage
– Normally clear vitreous humor becomes
discolored
– Detached retina can occur
– Control of blood sugar slows the
progression
AREDs
• Presbyopia
– Inability to focus clearly on near objects as
one ages
• Bifocal lenses can help “near” vision
Normal
Prescriptio
n
Near
Vision
Prescriptio
n
Age-Related Eye
Diseases
Binocular Vision and Depth Perception
• Binocular vision ~ coordinated eye
movements
• Strabismus ~ misaligned eyes
– Common at birth, but diminishes during the
first week (moving each eye at random)
• Depth perception
– A cerebral function based upon information
sent by the eye to the brain
Binocular Vision and Depth Perception
• The Visual Cliff
– Note the mother
attempting to coax the
infant into crossing the
apparent deep (cliff) side
– Infants are capable of
depth perception
– Depth perception is
mature at 6 years
– Gibson & Walk’s (1960)
classic experiment
Depth Perception
Held and Hein involved kittens in active and passive movement. The researchers
concluded that the active movement benefited the kittens’ development of
depth perception. Passive movement did not.
Depth Perception
• Motion hypothesis
– Individuals must interact with objects that
move in order to develop a normal
repertoire of visual-spatial skills
– Movement does not need to be self-induced
Depth Perception and Sport Success
• Accurate depth perception is task
specific
– Tennis vs. football
• Athletes without stereo vision
– The central nervous system can use
shadows, ball texture, and projectile size to
perceive depth
Field of Vision
• Refers to the entire extent of the
environment that can be seen without a
change in fixation of the eye
– Normal lateral peripheral vision is a little
greater than 90 degrees from straight ahead
(180 degrees total)
– Normal vertical peripheral vision is 47
degrees above and 65 degrees below visual
midline
Field of Vision
• Infant’s field of vision
– At 2 months ~ peripheral vision is 15
degrees lateral of central vision
– At 7 weeks ~ peripheral vision is 35 degrees
lateral of central vision
Field of Vision
• David’s 1987
experiment
examining
peripheral vision
processing
during the
performance of
a catching task
Field of Vision
• David’s experiment
– Assessed peripheral vision in children and
adults in real-world settings
– Peripheral information given to subjects
during a performance of ball-catching
– Required dual processing of information
– 9 year olds made significantly more
mistakes in ball catching compared to a
single task performance
Aging and Depth Perception and
Field of Vision
• Both disease (AMD) and anatomical
facial changes may cause a loss of
depth perception/field of vision with age
– Change in facial structure
– Senile ptosis
• Drooping of the eyelid
– Loss of fat tissue around orbital socket
Eye Dominance
• Refers to the ability of one eye to lead the
other in tasks involving visual tracking and
visual fixation
• Hole-in-card test
• Established between ages 3-5 years
Eye Dominance
• Unilateral dominance
– Right-eyed and right-handed
– Left-eyed and left-handed
• Crossed-lateral dominance
– Right-eyed and left-handed
– Left-eyed and right handed
Eye Dominance
• Eye dominance and motor performance
– Unilaterals are superior to crossed-laterals
in several motor tasks
– However, crossed-laterals may have an
advantage in baseball batting
• A right handed batter with left-eye dominance
• Dominant eye is closer to the pitcher
– This trait is more common among baseball
players than in the general population
Tracking and Object Interception
• Tracking an object allows the performer to gain
important information about the flight path of
the object
• Smooth pursuit system
– Matching of eye movement speed and speed of a
projectile
• Saccadic eye-movement system
– Corrects differences between projectile location
and eye fixation
Tracking and Object Interception
40-52
weeks
Can track a 180 degree arc
5-6 yr
Can track objects in horizontal
plane
8-9 yr
Can track balls that travel in arc
Tracking and Object Interception
• Bassin anticipation
time
• Coincidenceanticipation
– Process involving
object interception
Tracking and Object Interception
• Factors influencing
• Boys perform better
success in tracking and than girls
interception
• Very slow and very
– Object speed
fast moving objects
– Object predictability
result in greater
– Viewing time
performance error
– Gender
– Age
• Sport participation and
video games may be a
better predictor than age
Motor Development of
Children with Visual
Impairments
Blindness
• A definition of blindness is based upon
distance vision
• Ranges from 20/200 (80% loss of vision) to
total blindness
• Because visual curiosity elicits movement, the
unsighted child is not visually motivated to
explore the unseen world
Blindness
• Head and trunk
control
– Curiosity encourages
lifting head and trunk
in sighted children
– Unsighted child
fusses when in a
prone position –
parent places child
on the back which
does not help with
head and trunk
control
• Independent sitting
– Occurs in sighted
children between 4
and 8 months
– An unsighted child
can perform this task
between 4 and 8
months if the parents
have prepared the
child
• Need control over
head, neck, and trunk
Blindness
• Creeping
–
•
Independent
walking
By 10 months a sighted child
can support him/herself on
hands and knees to creep
and explore
– An unsighted child has no
enticement to explore
– Noise-making toys help the
unsighted child to creep
– Both sighted and
unsighted children are
able to walk
independently at the
same time
– However, this task is
usually delayed in
unsighted children
Blindness
• Prehension
– The ability to grasp
objects
– Vision is extremely
important in
performing the task of
prehension
– The unsighted child
exhibits a delay
• Vision is important in
prehension
development
– Child will reach for
objects
– Vision helps the child
to close the hands
around the object
– Errors can be
corrected throughout
the reaching process
Blindness
• Play
• Play is an important
learning medium
– For the sighted child,
play is spontaneous
• The unsighted child
– The unsighted child is
will do little more
inactive and shows
than rock or tap the
no desire to
fingers without help
experiment with the
environment
Motor performance of sighted
and visually impaired children
Nonvisual Senses
Proprioceptive System
• The ability to be aware of location and
movements in space without visual references
• A factor contributing to the development of
body awareness, spatial awareness, and
directional awareness
Proprioceptive System
• Mechanoreceptors
– Muscle spindles
– Golgi tendon organs
– Joint receptors
– Vestibular apparatus
Proprioceptive System
• Muscle spindles
– Can gauge the amount of
tension within the muscle
– Senses how the muscle is
stretched
– Classic “knee jerk”
• Golgi tendon organs
– Monitors tension in the
muscle’s tendon
– Feedback in force
development
Proprioceptive System
• Joint receptors
– “Limit detectors”
– Fire at a joint’s extreme range of motion
Proprioceptive System
• Vestibular apparatus
– Located in the inner
ear
– Rotational motion
• Semicircular canals
(angular
accelerometers)
– Linear acceleration
• Otolith organs (utricle
and saccule)
Copyright © The McGraw-Hill Companies, inc. Permission required for reproduction or display.
Auditory System
• Auditory
perception
– Auditory stimuli
received,
selected,
organized, and
interpreted
Copyright © The McGraw-Hill Companies, inc. Permission required for reproduction or display.
Auditory System
• Prenatal babies are capable of hearing during
the last few months of pregnancy
• At birth, the ear is structurally ready, but fluid in
the inner ear prevents sound wave travel for a
few days
• It is believed that the sound threshold is high
in newborns, thus requiring a very loud sound
Auditory System
• 0-3 months
– Infant enjoys hearing parents’ voices
– Responds better to Mother’s voice because of the
association to food and comfort
– Recognize tone only
• 4-7 months
–
–
–
–
Recognize some components of speech
This milestone is critical in development
By month 7, babies should respond to their name
Babbling should be encouraged
Auditory System
• 8-12 months
– Produce recognizable sounds
– Sophisticated babbling
– Can respond to simple verbal requests
• “Where’s Daddy?” Baby points to Daddy.
• 1-2 years
– Can name family members and simple objects
• Hearing impairments should be recognized before age 3
years
Cutaneous System
• Tactile sensitivity (skin)
• Responses to tactile stimulation
– Reflex response
• Babinski reflex
– Withdrawal response
• Move away from unpleasant or painful object
– Approach behaviors
• Response to kisses and hugs
Cutaneous System
• First system to develop
– Fetus responds to light stroking inutero
• Sensitivity to tactile stimulation is
greatest in the mouth, lips, tongue of
neonate
– Helps child to explore world
Cutaneous System
• Romberg’s Sign disease
– Varying degrees of damage to sensory
receptors
• In soles of feet
– Experience difficulty in standing, especially with closed
eyes
• In hands or fingers
– Fine motor manipulation is a problem