Photopic Vision
- Day time / High level artificial illumination
- Central viewing
- Cones
- 20/20 visual acuity
Mesopic Vision
- Mixture of Day / Night
- Most dangerous
- Both viewing techniques
- Cones / Rods
- Visual acuity varies
Scotopic Vision
- Night time
- Scanning techniques
- Rods
- 20/200 visual acuity unaided
Day Blind Spot
A 5.5° - 7.5° blind spot, located 15° from the fovea, originating where the optic nerve attaches to the retina. No cones or rods are present at attachment point and we compensate with binocular vision
Night Blind Spot
A 5° - 10° blind spot, due to the lack of rods present in the fovea centralis and parafovea. Compensated with “Off-center” viewing which is 10° above, below and to the side of the object and proper scanning techniques.
Dark Adaptation
Process in which the eyes increase their sensitivity to low levels of illumination. Time required to fully adapt is based off starting level of illumination ranging from 30 - 45 minutes. Exposure to harsh sunlight for 2 - 5 hours decreases visual sensitivity for up to 5 hours and can persist for several days.
Spatial Disorientation NVG Aggravating Factors
- Degraded Visual Acuity
- Fatigue
- High Task Loading
- Limited FOV
- Inexperience
- Aircraft Banks > 30°
- 3 Axis Head Movements
- Significant or Abrupt Aircraft Maneuvers
Visual Illusions
- Autokinesis
- False Horizon
- Fascination/Fixation
-Confusion with Ground Lights - Crater Illusion
- Structural Illusion
- Size-Distance Illusion
- Size Constancy
- Shape Constancy
- Aerial Perspective
- Vection
- Height-Depth Perception Illusion
Autokinesis
Visually fixating on a light for about 6 - 12 seconds can cause the individual to perceive movement at up to 20° in any particular direction or several directions.
Structural Illusions
Caused by effects of rain, snow, sleet, heat waves or other visual obscurants. Straight lines appear curved, Single lights might appear as double.
Aerial Perspective
When visual cues are of a different size than expected. Misjudging short or stunted trees for a full grown trees therefore misjudging altitude.
Height-Depth Perception
Due to absent or insufficient visual cues, causing crewmembers to misjudge depth perception.
Vestibular Illusions
- Somatogyral Illusion
- Somatogravic Illusion
-Oculoargravic Illusion - Alternobaric Vertigo
Somatogyral Illusions
Caused when changes in pitch, roll or yaw stimulate semicircular canals and pilot is unable to interpret the sensations they are feeling.
- Leans
- Graveyard Spiral
- Coriolis Illusion
- Post Roll Illusion
Somatogravic Illusions
Caused when changes in gravity or linear acceleration stimulate the otolith organ
- G-Excess Illusion
- Elevator Illusion
Oculoargravic Illusions
Occurs due to misperception of movement of a fixed object relative to the pilot during change of direction
Alternobaric Vertigo
Changes in atmospheric pressure can sometimes lead to vestibular dysfunction, this may arise from changes in altitude, middle ear equilibration maneuver or pressure differences between the two ears.
Binocular Cues
Depends on slightly different view each eye has on an object. Generally useful for objects closer than 10 meters which makes it of little value in a flight environment.
Monocular Cues
Aid in distance estimation and depth perception. assisting in identifying possible hazards in reference to present altitude and position.
Geometric Perspective
Object may appear to have a different shape when viewed at varying distances and different angles
Linear Perspective
Parallel lines appear to converge as distance from the observer increases
Apparent Foreshortening
True shape of an object or terrain feature appears distorted. Round objects appear elliptical while square objects take the shape of a trapezoid
Vertical Position in the Field
Objects or terrain features farther away appear higher on the horizon while objects closer appear lower on the horizon
Retinal Image Size
An image focused on the retina is perceived by the brain to be of a given size
