movement and the changing senses

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 diseases (ARED) are the leading cause of loss of visual acuity

• Conditions/diseases– Age-related macular

degeneration– Glaucoma– 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– Wet form

• New blood vessels form behind the retina, leak, and destroy the macula

Amsler Grid

Normal

AMDVisual acuity = 20/50-20/100-total blindness

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

Prescription

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 researchersconcluded that the active movement benefited the kittens’ development ofdepth 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

• Coincidence-anticipation– Process involving

object interception

Tracking and Object Interception

• Factors influencing success in tracking and interception– Object speed– Object predictability– Viewing time– Gender– Age

• Sport participation and video games may be a better predictor than age

• Boys perform better than girls

• Very slow and very fast moving objects result in greater performance error

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– 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

• Independent walking– 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 – For the sighted child,

play is spontaneous– The unsighted child is

inactive and shows no desire to experiment with the environment

• Play is an important learning medium

• The unsighted child will do little more than rock or tap the fingers without help

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)

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Auditory System

• Auditory perception– Auditory stimuli

received, selected, organized, and interpreted

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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