Neurological Aspects of Aviation Medicine

Abstract

Neurological Aspects of Disorientation in Aircrew Spatial disorientation is a term used in aviation medicine to describe a group of incidents, occurring in flight, where the aviator has a false perception of the position, attitude or motion of either himself or his aircraft. Only on rare occasions is the disorder of perception caused by disease, commonly it is the manifestation of a natural limitation of sensory function. In flight, man is taken out of his normal terrestrial environment and exposed to patterns of linear and angular motion to which his sensory systems are not functionally adapted. Spatial disorientation is thus one manifestation of the physiological and psychological cost of attempting to live and work in an unnatural environment. Early in the history of powered flight it was recognized that when the pilot was deprived of vision he was unable to maintain adequate orientation from information provided by vesti-bular receptors and from other mechanoreceptors in the skin, the capsules of joints and supporting tissues (Head 1920, Wulfften Palthe 1922). These nonvisual sensory systems, though adequate transducers of the linear and angular accelerations experienced by man during normal locomotion on the surface of the earth, were found to give either inadequate or inappropriate responses to the linear and angular motion stimuli of the flight environment. Thus, if the pilot were not to become disorientated when flying in cloud or at night his senses had to be complemented by instruments which provided symbolic information from which he could determine the attitude and motion of his aircraft. Over the years, the accuracy, reliability and ease of interpretation of instrument displays has been progressively improved. Nevertheless, incidents still occur in which flying personnel fail to perceive correctly the orientation of their aircraft, or they have to resolve a perceptual conflict generated by veridical visual cues and false vestibular and kinwsthetic cues. Types ofSpatial Disorientation Spatial disorientation is commonly thought of as a false sensation of aircraft attitude or motion. Typical examples are: the 'leans', in which the pilot feels that the aircraft is banked when instruments indicate that it is flying straight and level: the vertigo which occurs on recovery from a prolonged spin or rolling manceuvre: the apparent change in aircraft attitude which can accompany linear acceleration or deceleration in the line of flight (the somatogravic illusion). Such illusions are qualitatively false perceptions of aircraft orientation, and are primarily caused by limitations of vestibular and kinesthetic mechanisms (Melvill Jones 1966). These illusions have been extensively studied and described (