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Vision, Visual Illusions, and Disorientation


Vision, Visual Illusions, and Disorientation. Characteristics of Light ... Examples of visual illusions. Geometric optical illusions /page 118 ... – PowerPoint PPT presentation

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Title: Vision, Visual Illusions, and Disorientation

Vision, Visual Illusions, and Disorientation
Characteristics of Light
  • Light-is radiant energy which is capable of
    exiting the retna of the eye and is visible
    radiant energy
  • Reflected light-off a surface gives off
  • Absorbed light-on a surface gives off
  • Contrast-the relationship of a target to its
    background brightness
  • Refraction-when light passes through a medium of
    different density it is bent
  • Color-variations in wavelengths give rise to the
    perception of color (color blindness-unable to
    see red and green)

  • Pupil-aperture that controls the amount of light
    entering the eye
  • Iris-muscles that adjust the pupil
  • Cornea-transparent lense on front of the eye
    which focuses light to the back of the eye
  • Retina-back of the eye which the cornea focuses
    the light to
  • Fovea-center of retina has light receptors
    (rods on the outside pick up dim
    light/cones in the center pick up brighter light)

  • When the amount of light varies an adaptation
    takes place from the use of cones to rods (day to
    night) and rods to cones (night to day)
  • The adaptation process varies with age

Variables of visual acuity
  • Visual acuity is what a person can read off of a
    chart at 20 feet
  • Age decrease visual acuity (at age 40 it begins
    to decrease until at age 65 it is half of what it
  • Brightness affects visual acuity
  • Contrast affects visual acuity
  • Glare affects visual acuity

3 safety of flight visual ranges
  • Overhead panel-13-16 inches
  • Instrument panel-30-35 inches
  • Infinity-outside world
  • Deterioration of these ranges can lead to a false
    reading or missing traffic and needs to be

Visual Perception
  • Vision-eye-brain-experience and memory-pilot
    action aircraft response-visual feedback
  • However the inner ear also sends signals to the
    brain that affects visual perception
  • Motion-inner ear-brain-experience and
    memory-pilot action-aircraft response-motion

The Blind Spot
  • Each eye has a blind spot that is filled by the
    other eye when using binocular vision
  • If vision of an object by one eye is obstructed
    by a windshield then the visual target could be
    in the blind spot
  • See example page 115, Fig 5.7

Cues that help or hinder depth perception
  • Binocular vision
  • Perspective
  • Apparent movement of the object
  • Superposition
  • Relative size
  • Height of an object in the plane
  • Texture gradient

Hypoxia and smoking
  • Hypoxia-condition resulting from an oxygen
    deficiency (8000 feet plus)
  • Differs with different individuals
  • Reduces night vision and side effects
  • Smoking introduces carbon monoxide to the blood
    stream and reduces the flow of oxygen to the
  • A heavy smoker can get hypoxic at 5000 feet

Positioning and sitting
  • Sitting in the proper eye position is important
    in preventing accidents on final approach caused
    by eliminating view of the landing zone on final
    from poor eye positioning caused by improper

Examples of visual illusions
  • Geometric optical illusions /page 118
  • Depth and distance illusions/page119

Illusions on the ground
  • Illusion of moving when the gate is moving
  • Blowing snow or rain can give the illusion that
    the aircraft is moving
  • Pilots eye can misjudge the speed and can cause
    excessive speeds
  • Rain and precipitation and night can affect
  • Mist and fog can influence judgement

Takeoff Illusions
  • Accelerations could lead to illusions of turning
  • Acceleration- gives a pitching up sensation and
    can cause a tendency to push down
  • Deceleration- can cause a pitch down sensation
    and a tendency to pull up
  • After takeoff-false horizon perception can occur
    when stars appear as lights on a runway

Cruise Illusions
  • Prolonged turning-can create an illusion of a
    holding pattern
  • Auto kinesis-is the apparent moving of a
    stationary light at night
  • Evaluation of an approaching object(aircraft,
    mountains etc) and the proper assessment of
    collision risk
  • The blind spot

Approach and landing illusions
  • The most critical phase of flight and the most
    fatigued potential phase of the flight and can
    include adverse weather…..error can be
  • Sloping terrain-can give the illusion of being to
    low or to high depending on which way the runway
    slopes on landing
  • Runway width and lighting intensity-the wider and
    the brighter, the more closer the aircraft feels

Black Hole effect on landing
  • Occurs when approaching airports at night over an
    unlit area
  • Causes an illusion of height/giving way for a
    height higher than reality
  • Pago Pago 1974- Boeing 707 crashes short of
    runway killing 96 people on board

Measures to prevent illusions
  • Step1-all must agree that visual illusions are
    normal phenomenon and educate
  • Step2-Get to understand the nature and situations
    where they will be encountered
  • Step3-Brief the possibility of such an illusion
  • Step4-publish it where necessary for certain
    geographical areas
  • Step5-Correct manufacturers design

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