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Shappell, 1996
VISION AND VISUAL VISION AND VISUAL ILLUSIONS IN FLIGHTILLUSIONS IN FLIGHT
1053
LCDR Scott A. ShappellNaval Safety Center
Shappell, 1996
The Human Eye
Anatomical Vision: Duplicity TheoryCones and Rods
ConesDaylight visionDetailed high resolutionColor visionMotion detectionFovea for central vision
Shappell, 1996
The Human EyeThe Human Eye
RodsNighttime visionPoor detail Insensitive to colorPoor motion detectionPeripheral vision
At night, utilize rods by looking at dimly lit objects approx. one hand width away from them
Shappell, 1996
The Human Eye in AviationThe Human Eye in Aviation
Implications for Aviation:Implications for Aviation: Low illumination, central field of vision is Low illumination, central field of vision is
functionally blind, so we must adapt a mode functionally blind, so we must adapt a mode of looking at the side of objectsof looking at the side of objects
Functional Vision: Functional Vision: Pattern recognition and visual guidancePattern recognition and visual guidance Reading/walkingReading/walking
Implications for Aviation:Implications for Aviation: Moving without awareness --catastrophyMoving without awareness --catastrophy
Shappell, 1996
Human Visibility
Visibility: how well human eye can see Contrast is key factor Implications for aviation:
Ability to recognize hazards is degradedAbility to steer unaffected
“Black Hole” approaches at night:Area under aircraft dark, featurelessPilots overestimate altitude, fly too low AWARENESS!
Shappell, 1996
Vision and Midair CollisionsVision and Midair Collisions
See and Avoid PrincipleSee and Avoid Principle Three most common mid-air Three most common mid-air
collisions:collisions: Head onHead on Converging from side Converging from side Climb/descentClimb/descent
Examples of midairs due to Examples of midairs due to visual limitationsvisual limitations
Shappell, 1996
Distance Perception
Binocular CuesConvergence/Divergence, Retinal
Disparity Monocular Cues
Size and shape, Linear PerspectiveRelative Motion, InterpositionLight and Shadow
Shappell, 1996
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
Shappell, 1996
Visual Illusions
RELATIVE MOTIONMistake another aircraft’s movement
for own FALSE HORIZON
Cloud formations may be confused with horizon or ground
GROUND-LITE MISINTERPRETATIONConfusion of ground lights with stars
Shappell, 1996
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
Shappell, 1996
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
Shappell, 1996
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
Shappell, 1996
Effects of Lighting on Performance GLARE:
Direct Glare: light sources in field of viewReflected Glare: reflected by surface in
field of viewDiscomfort Glare: produces discomfort,
but does not necessarily interfere with performance
Disability Glare: reduces performanceBlinding Glare: no object can be seen