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

3. 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

4. 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

5. 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

6. 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!

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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