oculogravic illusion


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oculogravic illusion

An illusion caused by linear acceleration/deceleration, which gives a feeling of a false climb/descent, respectively. It is caused by the pilot's misinterpreting the information from the otolith organs. When the aircraft accelerates, on increasing engine power or reducing drag, the inertial force resulting from the increase in forward speed combines with the force of gravity to produce a resultant, which is inclined backward. (The otolith organ—the utricle—is shifted to the rear just as if the head were tilted backward; it, thus, sends erroneous signals to the brain that the head is tilting backward. This causes the pilot to sense a nose-high attitude.) If this resultant is used as a vertical reference, then the pilot will feel as if he or she and the aircraft are in a nose-up attitude. The pilot may try to correct this by pushing the stick forward. Conversely, when an aircraft decelerates, on decreasing engine power or by extending air brakes, the resultant vector swings forward and the pilot perceives that the aircraft has pitched down. The situation is unlikely to occur if either the visual clues are available or the pilot cross-checks the instruments. Also known as an agravic illusion.
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