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SPATIAL DISORIENTATION:
Seeing Is Not Believing
Spatial Orientation
Spatial orientation defines our natural ability to maintain our body orientation
and/or posture in relation to the surrounding environment (physical space) at rest
and during motion. Genetically speaking, humans are designed to maintain spatial
orientation on the ground. The flight environment is hostile and unfamiliar to the
human body; it creates sensory conflicts and illusions that make spatial orientation
difficult, and, in some cases, even impossible to achieve. Statistics show that between
5 to 10% of all general aviation accidents can be attributed to spatial disorientation,
and 90% of these accidents are fatal.
Spatial Orientation on the Ground
Good spatial orientation on the ground relies
on the effective perception, integration,
and interpretation of visual, vestibular (organs
of equilibrium located in the inner ear), and
proprioceptive (receptors located in the skin,
muscles, tendons, and joints) sensory information.
Changes in linear acceleration, angular acceleration,
and gravity are detected by the vestibular
system and the proprioceptive receptors,
and then compared in the brain with visual information
(Figure 1).
Spatial Orientation In Flight
Spatial orientation in flight is sometimes difficult to achieve because the various
types of sensory stimuli (visual, vestibular, and proprioceptive) vary in magnitude,
direction, and frequency. Any differences or discrepancies between visual, vestibular,
and proprioceptive sensory inputs result in a “sensory mismatch” that can produce
illusions and lead to spatial disorientation.
Vision and Spatial Orientation
Visual references provide the most important sensory information to maintain
spatial orientation on the ground and during flight, especially when the body and/or
the environment are in motion. Even birds, reputable flyers, are unable to maintain
spatial orientation and fly safely when deprived of vision (due to clouds or fog).
Only bats have developed the ability to fly without vision but have replaced their
vision with auditory echolocation. So, it should not be any surprise to us that, when
we fly under conditions of limited visibility, we have problems maintaining spatial
orientation.
Figure 1
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Central Vision
Central vision, also known as foveal vision is involved with the identification of
objects and the perception of colors. During instrument flight rules (IFR) flights,
central vision allows pilots to acquire information from the flight instruments that
is processed by the brain to provide orientational information. During visual flight
rules (VFR) flights, central vision allows pilots to acquire external information (monocular
and binocular) to make judgments of distance, speed, and depth.
Peripheral Vision
Peripheral vision, also known as ambient vision, is involved with the perception
of movement (self and surrounding environment) and provides peripheral reference
cues to maintain spatial orientation. This capability enables orientation independent
from central vision and that is why we can walk while reading. With peripheral vision,
motion of the surrounding environment produces a perception of self-motion
even if we are standing or sitting still.
Visual References
Visual references that provide information about distance, speed, and depth of
visualized objects include:
Comparative size of known objects at different distances.
Comparative form or shape of known objects at different distances.
Relative velocity of images moving across the retina. Nearby objects are perceived
as moving faster than distant objects .
Interposition of known objects. One object placed in front of another is perceived
as being closer to the observer.
Varying texture or contrast of known objects at different distances. Object detail
and contrast are lost with distance.
Differences in illumination perspective of objects due to light and shadows.
Differences in aerial perspective of visualized objects. More distant objects are seen
as bluish and blurry.
The flight attitude of an airplane is generally determined by the pilot’s visual
reference to the natural horizon. When the natural horizon is obscured, attitude can
sometimes be maintained by visual reference to the surface below. If neither horizon
nor surface visual references exist, the airplane’s attitude can only be determined by
artificial means such as an attitude indicator or other flight instruments. Surface references
　
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