Vestibular habituation in flightcrew

Vestibular habituation is a general reaction to any repetitive sensory stimulation. It can be characterized by four main features: acquisition, retention, loss or dishabituation, and transfer. This study concerns three groups of subjects: The first group consists of a) 27 pilots at present serving in the French Air Force, b) 12 pilots at present serving in the major civil airlines, c) 8 navigators, radio-navigators, and crew mechanics, some of whom are flying club pilots, and d) 3 professional pilots trained in flying clubs. All of these subjects had more than 2000 h flying time. They were from 27 to 50 years old. The second group consists of airline stewards. The third group consists of trainee pilots still in flying school. All of these subjects were examined for their suitability, in particular undergoing a damped swing test. The first oscillation was in an anticlockwise direction and the damping extended over 20 periods. The following parametre was measured: the ratio of total left nystagmus frequency to total right nystagmus frequency. In "normal" control subjects the ratio is greater than 1. The results were: The first group: In 41 out of 50 subjects, the ratio of left tremors frequency to right tremors frequency was less than or approximately equal to 1. In the second group: The results showed no significant differences in comparison with a control group of subjects. In the third group: Zero flying time--the results were identical with those of control subjects; 40 h flying time--the ratio approached 1; 100 h flying time--the ratio was less than 1. Vestibular habituation, that is inversion of the preponderance of the total number of left tremors over the total number of right tremors, was observed in the technical flightcrew. The appearance of this inversion during the pilots' training was studied and its retention tested. This test for showing vestibular habituation may be of use for monitoring the function of equilibrium and the development of habituation during flight training. In this report, we shall first review the definition and characteristics of vestibular habituation, and the main body of recent work on this phenomenon in flightcrew. Our own findings will be then presented.