Shappell, 1996 VISION AND VISUAL ILLUSIONS IN FLIGHT 1053 LCDR Scott A. Shappell Naval Safety Center

Shappell, 1996 The Human Eye 4 Anatomical Vision: Duplicity Theory 4Cones and Rods 4 Cones 4Daylight vision 4Detailed high resolution 4Color vision 4Motion detection 4Fovea for central vision

Shappell, 1996 The Human Eye 4 Rods 4Nighttime vision 4Poor detail 4Insensitive to color 4Poor motion detection 4Peripheral vision 4 At night, utilize rods by looking at dimly lit objects approx. one hand width away from them

Shappell, 1996 The Human Eye in Aviation 4 Implications for Aviation: 4Low illumination, central field of vision is functionally blind, so we must adapt a mode of looking at the side of objects 4 Functional Vision: 4Pattern recognition and visual guidance 4Reading/walking 4 Implications for Aviation: 4Moving without awareness --catastrophy

Shappell, 1996 Human Visibility 4 Visibility: how well human eye can see 4 Contrast is key factor 4 Implications for aviation: 4Ability to recognize hazards is degraded 4Ability to steer unaffected 4 “Black Hole” approaches at night: 4Area under aircraft dark, featureless 4Pilots overestimate altitude, fly too low 4AWARENESS!

Shappell, 1996 Vision and Midair Collisions 4 See and Avoid Principle 4 Three most common mid-air collisions: 4Head on 4Converging from side 4Climb/descent 4 Examples of midairs due to visual limitations

Shappell, 1996 Distance Perception 4 Binocular Cues 4Convergence/Divergence, Retinal Disparity 4 Monocular Cues 4Size and shape, Linear Perspective 4Relative Motion, Interposition 4Light and Shadow

Shappell, 1996 Visual Illusions 4 Misinterpretation of sensory data 4 Unavoidable during ambiguous, obscured or absent visual cues 4 AUTOKINESIS 4Static light appears to move when stared at in the dark; reduced by visual scanning

Shappell, 1996 Visual Illusions 4 RELATIVE MOTION 4Mistake another aircraft’s movement for own 4 FALSE HORIZON 4Cloud formations may be confused with horizon or ground 4 GROUND-LITE MISINTERPRETATION 4Confusion of ground lights with stars

Shappell, 1996 Visual Illusions 4 WATERFALL EFFECT 4Rotor downwash gives false cue of climb 4 HEIGHT ILLUSION 4Flying over low contrast, illusion of high alt 4 FLICKER VERTIGO 4Flicker between 4-20 cycles/sec 4 SIZE-DISTANCE ILLUSION 4Viewing 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 l Dark to light: 50% recovery in 90 s l Light to dark: Up to 40 minutes –Under low levels of illumination, more subject to illusions

Shappell, 1996 Human Vision l PHOTOPIC VISION –High levels of illumination, both rods and cones are activated l SCOTOPIC VISION l Low levels of illumination, cones are inactive and vision is accomplished by rods l Purkinge Effect: shift from photpic to scotopic vision

Shappell, 1996 Effects of Lighting on Performance 4 GLARE: 4Direct Glare: light sources in field of view 4Reflected Glare: reflected by surface in field of view 4Discomfort Glare: produces discomfort, but does not necessarily interfere with performance 4Disability Glare: reduces performance 4Blinding Glare: no object can be seen

Shappell, 1996 Spatial Disorientation 4 SPATIAL DISORIENTATION 4Mismatch of visual, vestibular, and somatosensory cues 4 DISORIENTATION EFFECTS FROM FALSE SENSATIONS: 4Post-rotatory nystagmus/Graveyard spin 4Cross-coupling/Coriolis effect 4Occulogravic illusion