VISION AND VISUAL ILLUSIONS IN FLIGHT
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VISION AND VISUAL ILLUSIONS IN FLIGHT. LCDR Scott A. Shappell Naval Safety Center. 1053. The Human Eye. Anatomical Vision: Duplicity Theory Cones and Rods Cones Daylight vision Detailed high resolution Color vision Motion detection Fovea for central vision. The Human Eye. Rods

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VISION AND VISUAL ILLUSIONS IN FLIGHT

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VISION AND VISUAL ILLUSIONS IN FLIGHT

LCDR Scott A. Shappell

Naval Safety Center

1053


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The Human Eye

  • Anatomical Vision: Duplicity Theory

    • Cones and Rods

  • Cones

    • Daylight vision

    • Detailed high resolution

    • Color vision

    • Motion detection

    • Fovea for central vision


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The Human Eye

  • Rods

    • Nighttime vision

    • Poor detail

    • Insensitive to color

    • Poor motion detection

    • Peripheral vision

  • At night, utilize rods by looking at dimly lit objects approx. one hand width away from them


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The Human Eye in Aviation

  • Implications for Aviation:

    • Low illumination, central field of vision is functionally blind, so we must adapt a mode of looking at the side of objects

  • Functional Vision:

    • Pattern recognition and visual guidance

    • Reading/walking

  • Implications for Aviation:

    • Moving without awareness --catastrophy


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Human Visibility

  • Visibility: how well human eye can see

  • Contrast is key factor

  • Implications for aviation:

    • Ability to recognize hazards is degraded

    • Ability to steer unaffected

  • “Black Hole” approaches at night:

    • Area under aircraft dark, featureless

    • Pilots overestimate altitude, fly too low

    • AWARENESS!


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Vision and Midair Collisions

  • See and Avoid Principle

  • Three most common mid-air collisions:

    • Head on

    • Converging from side

    • Climb/descent

  • Examples of midairs due to visual limitations


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Distance Perception

  • Binocular Cues

    • Convergence/Divergence, Retinal Disparity

  • Monocular Cues

    • Size and shape, Linear Perspective

    • Relative Motion, Interposition

    • Light and Shadow


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Visual Illusions

  • Misinterpretation of sensory data

  • Unavoidable during ambiguous, obscured or absent visual cues

  • AUTOKINESIS

    • Static light appears to move when stared at in the dark; reduced by visual scanning


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Visual Illusions

  • RELATIVE MOTION

    • Mistake another aircraft’s movement for own

  • FALSE HORIZON

    • Cloud formations may be confused with horizon or ground

  • GROUND-LITE MISINTERPRETATION

    • Confusion of ground lights with stars


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Visual Illusions

  • WATERFALL EFFECT

    • Rotor downwash gives false cue of climb

  • HEIGHT ILLUSION

    • Flying over low contrast, illusion of high alt

  • FLICKER VERTIGO

    • Flicker between 4-20 cycles/sec

  • SIZE-DISTANCE ILLUSION

    • Viewing light as changing in brightness


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Dark Adaptation

  • Sensitivity to light is impaired after periods of bright light exposure

  • Depends on time for receptors to bleach

    • Dark to light: 50% recovery in 90 s

    • Light to dark: Up to 40 minutes

  • Under low levels of illumination, more subject to illusions


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Human Vision

  • PHOTOPIC VISION

    • High levels of illumination, both rods and cones are activated

  • SCOTOPIC VISION

  • Low levels of illumination, cones are inactive and vision is accomplished by rods

  • Purkinge Effect: shift from photpic to scotopic vision


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Effects of Lighting on Performance

  • GLARE:

    • Direct Glare: light sources in field of view

    • Reflected Glare: reflected by surface in field of view

    • Discomfort Glare: produces discomfort, but does not necessarily interfere with performance

    • Disability Glare: reduces performance

    • Blinding Glare: no object can be seen


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Spatial Disorientation

  • SPATIAL DISORIENTATION

    • Mismatch of visual, vestibular, and somatosensory cues

  • DISORIENTATION EFFECTS FROM FALSE SENSATIONS:

    • Post-rotatory nystagmus/Graveyard spin

    • Cross-coupling/Coriolis effect

    • Occulogravic illusion


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