Movement and the Changing Senses

Chapter 9

McGraw-Hill/Irwin © 2012 McGraw-Hill Companies. All Rights Reserved.

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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.

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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 flattenContraction of the ciliary muscles causes the lens to become more spherical

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Understanding the Mechanics of Vision

Accommodation is the adjustment of the eye to variations in distanceThe retina contains two photoreceptors

Rods are responsible for vision in low illumination (night vision)Cones are responsible for color vision and visual acuity

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Understanding the Mechanics of Vision

Macula lutea: an oval yellow spot at the center of the retina

Fovea centralis (point of best vision) is located here

Cone cells are concentratedThere is an absence of rod cells

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Retina

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Understanding the Mechanics of Vision

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Physical Development of the Eye

The eye develops as an outgrowth of the forebrain

Part of the central nervous system6 cranial nerves govern vision

At birthThe eye is hyperopic (light focuses behind the retina)The retina contains mostly rod cells

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At birth

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Physical Development of the Eye

At 1 month postnatalCone cells appear

At 8 months postnatalMacula is mature

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Development of Selected Visual Traits and Skilled Motor

Performance

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Visual Acuity

Static visual acuityTarget and performer are stationary20/20 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.

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Visual Acuity

Degree of detail that can be seen in an objectA Snellen eye chart is used to determine visual acuity

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Visual Acuity

This Snellen eye chart is used with children in grades K-1 who may not be capable of letter recognition

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Visual Acuity

Birth 20/200 and

20/4006

months20/200

1 yr. 20/504-5 yr. 20/20

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Visual Acuity

Dynamic visual acuityAbility to see the detail in moving objectsAbility of the central nervous system to estimate an object’s directionAbility of the ocular-motor system “to catch” and “to hold” an object’s image on the eye’s fovea long enough to see detail

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Visual Acuity and Motor Performance

Both static and dynamic visual acuity play keys roles Dynamic visual acuity is highly correlated with success in

Free throw shootingBall catching

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Visual Acuity and Exercise

Aerobic activities appear to improve visual acuity for up to two hours post-exerciseIncrease in acuity due to increase in blood flow and oxygenation to the eye

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Visual Acuity and Aging

Age-related eye diseases (ARED) are the leading cause of loss of visual acuity

Conditions/diseases

Age-related macular degenerationGlaucomaCataractsSenile miosisDiabetic retinopathyPresbyopia

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AREDs

Age-related macular degeneration (AMD)Loss of central visionDry form

Breakdown of light sensitive cells in the maculaCentral vision affectedNot allowed to drive and will have trouble readingNo problem with general movement

Wet formNew blood vessels form behind the retina, leak, and destroy the macula

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AREDsNormal

AMDAmsler Grid

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AREDs

GlaucomaLeading cause of loss in visual acuity and blindnessHigh pressure in eyeLoss of peripheral visionEventual loss of central vision

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AREDs

CataractsClouding of the eye’s lensInitial symptoms include complaints of glare, colors that seem faded, and increased need for light when reading

Senile miosisNormal loss of light restriction to the eye with ageDecrease in resting diameter of the pupil

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AREDs

Diabetic retinopathyComplication of diabetesVessels in the retina may hemorrhageNormally clear vitreous humor discolorsDetached retina can occur

PresbyopiaInability to focus clearly on near objects as one ages

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Binocular Vision and Depth Perception

Binocular vision ~ coordinated eye movements Strabismus ~ misaligned eyes

Common at birth, but diminishes during the first week

Depth perceptionA cerebral function based upon information sent by the eye to the brain

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Binocular Vision and Depth Perception

The Visual CliffNote the mother attempting to coax the infant into crossing the apparent deep (cliff) sideInfants are capable of depth perceptionGibson & Walk’s (1960) classic experiment

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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 = 90 degrees from straight ahead (180 degrees total)Normal vertical peripheral vision = 47 degrees above and 65 degrees below visual midline

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Field of Vision

David’s 1987 experiment examining peripheral vision processing during the performance of a catching task

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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 structureSenile ptosis

Drooping of the eyelid

Loss of fat tissue around orbital socket

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Eye Dominance

Refers to the ability of one eye to lead the other in tasks involving visual tracking and visual fixationHole-in-card test

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Eye Dominance

Unilateral dominanceRight-eyed and right-handedLeft-eyed and left-handed

Crossed-laterals dominanceRight-eyed and left-handedLeft-eyed and right handed

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Tracking and Object Interception

Tracking an object allows the performer to gain important information about the flight path of the objectSmooth pursuit system

Matching of eye movement speed and speed of a projectile

Saccadic eye-movement systemCorrects differences between projectile location and eye fixation

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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

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Tracking and Object Interception

Bassin anticipation timeCoincidence-anticipation

Process involving object interception

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Motor Development of Children with Visual

Impairments

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Blindness

A definition of blindness is based upon distance visionRanges 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

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Blindness

Head and trunk control

Curiosity encourages lifting head and trunk in sighted childrenUnsighted child fusses when in a prone position – parent places child on the back which does not help with head and trunk control

Independent sittingOccurs in sighted children between 4 and 8 monthsAn unsighted child can perform this task at the same time if the parents have prepared the child

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Blindness

CreepingBy 10 months a sighted child can support him/herself on hands and knees to creep and exploreAn unsighted child has no enticement to exploreNoise making toys help the unsighted child to creep

Independent walking

Both sighted and unsighted children are able to walk independently at the same timeHowever, this task is usually delayed in unsighted children

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Blindness

Prehension Vision is extremely important in performing the task of prehensionThe unsighted child exhibits a delay

Play For the sighted child, play is spontaneousThe unsighted child is inactive and shows no desire to experiment with the environment

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Bayley Scale Items

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Nonvisual Senses

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Proprioceptive System

The ability to be aware of location and movements in space without visual referencesA factor contributing to the development of body awareness, spatial awareness, and directional awareness

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Proprioceptive System

MechanoreceptorsMuscle spindlesGolgi tendon organsJoint receptorsVestibular apparatus

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Proprioceptive System

Muscle spindlesCan gauge the amount of tension within the muscleSenses how the muscle is stretched

Golgi tendon organsMonitors tension in the muscle

Joint receptors“Limit detectors”

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Classic Knee Jerk

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Proprioceptive System

Vestibular apparatusLocated in the inner earRotational motion

Semicircular canals (angular accelerometers)

Linear accelerationOtolith organs (utricle and saccule)

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Cutaneous System

Tactile sensitivity (skin)Responses to tactile stimulation

Reflex responseBabinski reflex

Withdrawal responseMove away from unpleasant or painful object

Approach responseResponse to kisses and hugs

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Key Terms