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 spatial  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. 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 does 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 be created there to be 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 (SA). (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 3-1  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 of the cube’s top face.  Eyes Figure 3-1.  Rubik’s cube graphic depicting the visual processing of information. 3-2