Physiology Of Spatial Orientation

Excerpt

Aviation-associated spatial disorientation, as described by Benson, occurs when “the pilot fails to sense correctly the position, motion, or attitude of his aircraft or of himself within the fixed coordinate system provided by the surface of the Earth and the gravitational vertical.” In other words, spatial orientation is the natural ability to maintain body orientation and/or posture in relation to one's environment while at rest and during motion. Humans are naturally designed to maintain orientation while on the ground in a two-dimensional environment. Aviation incorporates a three-dimensional environment and can lead to sensory conflicts, making orientation difficult or even impossible to maintain. Spatial disorientation is a phenomenon that is well known to aviators, but it remains unclearly defined and continues to be one of largest causes of aviation mishaps.

Spatial disorientation is achieved through three major sensory sources: visual, vestibular, and proprioceptive. To achieve appropriate orientation the body relies on accurate perception and cognitive integration of all three systems. If visual, vestibular, and proprioceptive stimuli vary in magnitude, direction and frequency the resulting effect can be spatial disorientation.

The human eye provides visual and spatial orientation, which is responsible for providing about 80% of the sensory inputs needed to maintain orientation. The vestibular system within the inner ear contributes 15%. Proprioceptive sensory inputs from receptors located in the skin, muscle, tendons, and joints account for 5% of the sensory information used to establish orientation. Complex coordination between these sensory inputs is then translated and interpreted by the brain. Misinterpretation or inaccuracy of these three sources of information can lead to “sensory mismatch,” resulting in a variety of visual or vestibular illusions.