Sensory Systems for Orientation
Orientation is the awareness of the position of the aircraft
and of oneself in relation to a specific reference point.
Disorientation is the lack of orientation, and spatia]
disorientation specifically refers to the lack of orientation
with regard to position in space and to other objects.
Orientation is maintained through the body's sensory organs
in three areas: visual, vestibular, and postural. The eyes
maintain visual orientation. The motion sensing system in
the inner ear maintains vestibular orientation. The nerves in
the skin, joints, and muscles of the body maintain postural
orientation. When healthy human beings are in their natural
environment, these three systems work well. When the
human body is subjected to the forces of flight, these senses
can provide misleading information, It is this misleading
information that causes pilots to become disoriented.
Eyes
Of all the senses, vision is most important in providing
information to maintain safe flight. Even though the
human eye is optimized for day vision, it is also capable
of vision in very low light environments. During the day,
the eye uses receptors called cones, while at night, vision is
facilitated by the use of rods. Both of these provide a level
of vision optimized for the lighting conditions that they
were intended. That is, cones are ineffective at night and
rods are ineffective during the day.
Rods, which contain rhodopsin (called visual purple), are
especially sensitive to light and increased light washes out
the rhodopsin compromising the night vision. Hence, when
strong light is momentarily introduced at night, vision
may be totally ineffective as the rods take time to become |
effective again in darkness. Smoking, alcohol, oxygen
deprivation, and age affect vision, especially at night. It
should be noted that at night, oxygen deprivation such as one
caused from a climb to a high altitude causes a significant
reduction in vision. A return back to the lower altitude will
not restore a pilot's vision in the same transitory period used
at the climb altitude.
The eye also has two blind spots. The day blind spot is the
location on the light sensitive retina where the optic nerve
fiber bundle (which carries messages from the eye to the
brain) passes through. This location has no light receptors,
and a message cannot he created there to he sent to the brain.
The night blind spot is due to a concentration of cones in an
area surrounding the fovea on the retina. Because there are
no rods in this area, direct vision on an object at night will
disappear. As a result, off-center viewing and scanning at
night is best for both obstacle avoidance and to maximize
situational awareness. [See the Pilot's Handbook of
Aeronautical Knowledge and the Aeronautical information
Manual (AIM) for detailed reading.
The brain also processes visual information based upon color,
relationship of colors, and vision from objects around us.
Figure 1-1 demonstrates the visual processing of information.
The brain assigns color based on many items to include an
object's surroundings. In the figure below, the orange square
on the shaded side of the cube is actually the same color
as the brown square in the center o the cube's top face. |
