1Topic 2.10 Vision AVMO 0019

  1. Learning Outcomes?
    • • Identify elements of the structure and function of the human visual system relevant to aviation.
    • • Differentiate between the functions of the focal and ambient visual systems.
    • • Describe the intrinsic physiological and perceptual limitations of the visual system, and how they contribute to visual illusions.
    • • Categorise common visual illusions, and identify flight scenarios in which they might occur.
    • • Demonstrate how to perform an efficient visual scan.
    • • Recommend techniques used to optimise unaided night vision
    • • Discuss the role of the visual physiology in the genesis, prevention and management of visual illusions in flight.
  2. Role of Vision in Flying?
    • • Most reliable sense
    • • VFR = “see and be seen”
    • • Provides 80% of spatial orientation cues
    • • Visual scanning
    • • Collision avoidance
    • • Depth & distance perception
    • • Information gathering - situational awareness
  3. Physiological Threats to visual performance in military aviation?
    • • +Gz
    • • Fatigue
    • • Hypoxia
    • • Medical conditions
    • • Medications
  4. Physical Threats to visual performance in military aviation?
    • • Lasers
    • • Birdstrike
    • • MDC splatter
    • • Wind blast
    • • Glare
    • • UV radiation
    • • Ionising radiation
    • • NVGs
  5. Distribution of rods and cones
    • Cone and Rod Sensitivities
    • 3 Functions of the Eye?
    • • Light Sense
    • • Photopic = lots of light = cones only
    • • Mesopic = some light = cones and rods
    • • Scotopic = no light = rods only
    • • Form Sense
    • • focal (central) vision vs. ambient (peripheral) vision
    • • Colour Perception
    • • stimulation of 3 types of cones
    • • red green and blue
  6. Photopic Vision?
    • -cones only
    • -colour vision
    • -bright light conditions
    • -macula-fovea
  7. Scoptopic vision?
    • -rods
    • -no light
    • -good for movement
  8. Mesopic vision?
    • -some light
    • -cones and rods
  9. Focal Vision ?
    • Cones
    • • Also called central or foveal vision
    • • High visual acuity
    • • Good colour vision
    • • Resolution of fine detail and object recognition
    • • Needs light - night blind spot
    • • Demands conscious awareness
    • • Orientation information presented by instruments
  10. Ambient Vision: ?
    • Rods
    • • Peripheral retina
    • • Low visual acuity
    • • Poor colour vision
    • • Sensitive to low light levels and movement
    • • Doesn’t always provoke conscious awareness
    • • Orientation information from external visual references
  11. Depth Perception?
    • • Depth perception is the visual ability to perceive the world in three dimensions
    • • Binocular cues
    • • Monocular cues
  12. Binocular (Physiological) Cues of Depth Perception?
    • • Convergence
    • • Accommodation
    • • Stereopsis
    • • All distance limited
  13. Monocular (Psychological) Cues of Depth Perception?
    • Size constancy
    • We judge distance to an object by its perceived size Relative motion (parallax)
    • Near objects move past quickly, distant - move very little Monocular Cues of Depth Perception
    • Aerial perspective
    • The effect the atmosphere has on the appearance of an object as it is viewed from a distance.
    • Overlap/Interposition
    • One object in front of another will obstruct the view of the farther object
    • Monocular Cues of Depth Perception
    • Linear perspective
    • parallel lines that recede into the distance appear to get closer together or converge.
  14. LIMITATIONS OF THE VISUAL SYSTEM?
  15. Perceptual Limitations?
    • • “Bottom up” processing - physiological
    • • “Top down” processing - psychological
    • • Is vision 100% reliable?
  16. Physiological Limitations?
    • • Focal Traps
    • • Empty Field Myopia
    • • Threshold for Acuity
    • • Saccadic vision
    • • Depth Perception
    • • Anatomical Blind Spot
    • • Perception Time
  17. 1. LIMITATIONS OF THE VISUAL SYSTEM Focal Traps?
    • • Focus on the foreground
    • • Functionally short-sighted (myopic)
    • • Examples
    • • Dirty transparencies
    • • Rain drops
    • • Bugs, Cracks/chips
    • • Windscreen wipers
    • • Not HUDs
  18. 2. LIMITATIONS OF THE VISUAL SYSTEM Empty Field Myopia?
    • • Causes - Poor visual cues
    • • High altitude
    • • IMC
    • • featureless terrain, etc
    • • Effects
    • • Eye’s focal “rest” position is 1 to 2 metres
    • • Functional myopia, can’t see distance
    • • Cure: push focus out to the wing tip
  19. 3. LIMITATIONS OF THE VISUAL SYSTEM Threshold of Acuity?
    • • The eye has a visual acuity threshold below which an object will go undetected
    • • More than 120 alternating white and black lines crowded side-by-side in a single degree of viewing space will appear
  20. 4. LIMITATIONS OF THE VISUAL SYSTEM Saccadic Movement?
    • • Rapid flicking movement of eyes
    • • Occurs when rotating/dizzy and during visual scan
    • • Retinal image blurs until the next point of fixation is reached
    • • Targets may not be perceived
  21. 5. LIMITATIONS OF THE VISUAL SYSTEM Limits of Depth Perception?
    • Binocular cues
    • • Stereopsis does not work beyond 200m
    • • Convergence and accommodation do not work beyond 6m
    • Monocular cues
    • • Linear perspective
    • • Overlap
    • • Size constancy
    • • All can lead to misperceptions of distance
  22. 6. LIMITATIONS OF THE VISUAL SYSTEM Anatomical Blind Spot?
    • Caused by lack of rods and cones at optic disc
  23. Visual Illusions can be either?
    • • Focal
    • • common when visual cues are inadequate or absent, eg. depth perception, night illusions
    • • processing errors, eg. expectancy
    • • Ambient
    • • false horizons
    • • vection illusions
  24. Focal Visual Illusions?
    • Brown Out
    • • Visual references lost due to dust
    • White Out
    • • Visual references lost due to snow or cloud layers
  25. Illumination Cues
    • • Which way is up?
    • • “Lean on the sun”
    • illusion
    • • Terrain contrast may be poor, hiding terrain features
    • • Purkinje shift
  26. Ambient Visual Illusions?
  27. False Horizon?
    • • Sloping cloud tops
    • • Ground lights
    • • Coastlines
  28. Vection Illusion?
    • • Movement in peripheral vision
    • • Hovering over water, long grass
    • • “Waterfall” Illusion
    • • Formation flying
  29. Examples of Specific Illusions?
    • • Certain illusions are known to occur in particular fight conditions:
    • • Approach and landing
    • • Mid-air collisions
    • • High speed, low level
    • • High altitudes
    • • Over water
    • • Flying at night
  30. 1. Illusions on Approach and Landing?
    • • Judging an approach depends on:
    • • Size and shape of runway – width, length, slope
    • • Changing runway perspective
    • • Ambient visual cues & motion parallax
    • • Terrain cues
    • • texture
    • • features, natural and man-made
    • • vegetation
  31. Longer runways?
    • • feel higher so fly lower
    • • may land short
  32. Shorter runway?
    • • feel lower so fly higher
    • • may land long
  33. Narrow runway:?
    • • looks further away
    • • risk late flare and landing short
  34. Wider runway:?
    • • feel close/low so approach high
    • • risk flaring early and landing long
  35. Terrain?
    • • Sloping terrain under approach path
    • • Featureless terrain
    • •snow
    • •smooth water
    • • Surrounding vegetation
  36. Runway Up-sloping?
    • •See more runway
    • •Feel high so fly low
  37. Runway Down-sloping?
    • •See less runway
    • •Feel low so fly high
  38. Preventing Midair Collisions?
    • • Scanning technique:
    • • Short, regularly spaced eye fixations across the field of vision
    • • Use both eye and head movements to maximise field of regard, and avoid aircraft structures
  39. 3. High Speed, Low Level?
    • • Visual performance degraded by:
    • • Blur zone
    • • Limited perception time
    • • Vibration
    • • Atmospheric conditions
    • • Other problems:
    • • Target acquisition more difficult
    • • Bird-strike more of a risk
  40. 4. High Altitude Flight?
    • • Likely Illusions:
    • • Empty field myopia
    • • Horizon illusions
    • • Other problems:
    • • Glare is worse
    • • UV radiation exposure, possible cataracts
  41. 5. Over-Water Flight?
    • Visual performance degraded by:
    • Poor height/motion cues
    • • Horizon definition
    • • Glare off water
    • • Empty field myopia
    • • Landing illusions
  42. Glare?
    • • Glare is an intrusive light source
    • • reduces visual performance
    • • increases with altitude
    • • Discomfort glare
    • • No degradation of visual performance but is uncomfortable, eg. causes squinting, blinking
    • • Disability glare
    • • Results in reduction in visual performance
    • • Types:
    • • veiling
    • • dazzle
    • • scotomatic (flash blindness)
  43. Glare protection?
    • • Sunglasses and helmet visors
    • • ND15 CR39 Lenses
    • • Neutral density
    • • 15% transmittance
    • • Impact resistant polycarbonate
    • • IR/UV filtering
    • • NOT polarizing
  44. 6. Flying at night Visual performance degraded by?
    • • Low light – rods used (mesopic and scotopic vision)
    • • Poor external visual cues
    • • Atmospheric conditions
    • • Physiological “Night” blind spot
    • • Empty field myopia
    • • Latent refractive disorders
    • • Fatigue
  45. Night Blind Spot?
  46. Latent Refractive Disorder
    • • Latent myopia unmasked at night
    • • Pupillary dilatation –large aperture
    • • Aberration
    • • Chromatic aberration cues lost
  47. Night Illusions?
  48. Autokinesis?
    • • Apparent motion of single stationary points of light in poor visual conditions
    • • Caused by involuntary eye movements Black Hole Illusion
    • • Runway lights visible
    • • No cultural lighting
    • • No terrain cues
    • • Poor horizon cues
    • • Controlled flight into terrain during approach
  49. Night Illusions?
  50. Landing illusions?
    • • Tendency to flare high
    • • Caused by:
    • •Poor height cues
    • •Lights wider & higher than runway
    • •Runway light intensity varies
    • •Meteorology
  51. round light confusion?
    • • Cultural lighting
    • • Stars
    • • Fishing boats
    • • Horizon illusions
  52. Maximising Night Vision?
    • • Good nutrition, vitamin A
    • • Avoid bright light during the day
    • • Properly dark adapt
  53. Quiz question 16:?
    • • Over long distances, the brain uses which cue to judge distance and depth:
    • a. Stereopsis
    • b. Convergence
    • c. Accommodation
    • d. Aerial perspective
Author
david_hughm
ID
328892
Card Set
1Topic 2.10 Vision AVMO 0019
Description
1Topic 2.10 Vision AVMO 0019.txt
Updated