Vision, Visual Illusions, and Disorientation

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Vision, Visual Illusions, and Disorientation
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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
  brightness
• Absorbed light-on a surface gives off
  illumination
• 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)

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Physiology

• 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)
  

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Adaptation

• 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

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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
  is)
• Brightness affects visual acuity
• Contrast affects visual acuity
• Glare affects visual acuity

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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
  corrected

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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
  feedback

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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

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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

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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
  brain
• A heavy smoker can get hypoxic at 5000 feet

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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
  seating

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Examples of visual illusions

• Geometric optical illusions /page 118
• Depth and distance illusions/page119

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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
  speed
• Mist and fog can influence judgement

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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

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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

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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
  catastrophic
• 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

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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

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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
  occurring
• Step4-publish it where necessary for certain
  geographical areas
• Step5-Correct manufacturers design

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