384 



MOTION SICKNESS, I 



of a preliminary evaluation of susceptibility 

 to motion sickness by exposure to the actual 

 working environment, has yet to be explored. 



Labyrinthine Tests and Tests of Balance 



Responses to rotation on the conventional 

 Baranj'' Chair test appear to have little re- 

 lation to susceptibility to motion sickness. 

 Results on 644 aviation cadets indicated 

 that qualification or non-qualification on the 

 Barany Chair test (according to the medical 

 criteria of the test) was unrelated to symp- 

 toms of motion sickness on a swing test 

 (76). Similarily, post-rotational nystagmus 

 was reported to be no different for a group 

 of men sent to shore duty because of sea- 

 sickness than for a random group of men 

 (17). 



Symptoms produced by injection of "hot" 

 or "cold" water into the external ear, i.e., 

 caloric vestibular tests, are not closely re- 

 lated to susceptibility to airsickness (38, 79, 

 85). The bulk of evidence suggests, there- 

 fore, that there is little, if any, relation 

 between the kinds of measurements fur- 

 nished by caloric or rotation tests and 

 susceptibility to motion sickness. There is 

 similarly no evidence that susceptibilitj^ to 

 motion sickness is a reflection of a hyper- 

 sensitive vestibular apparatus, at least as 

 indicated by measurements on the caloric 

 and Barany Chair tests. 



Studies were carried out on a group of 

 men highly susceptible to seasicloiess to dis- 

 cover if their balance was different from 

 normals (19). Two tests were used: (1) the 

 rail-walking test, which required the indi- 

 vidual to walk a thin wooden rail while 

 holding his hands behind his back, and (2) 

 the ataxiagraph test, which recorded the 

 amount of body sway while standing erect, 

 feet together, under eyes open and eyes 

 closed conditions. The susceptible men 

 were no different from normals in ability to 

 walk a thin rail. On the ataxiagraph, how- 

 ever, significantly greater body sway was 

 reported for the susceptible group. This 

 finding may be a reflection of some defect in 



the tonic vestibular mechanisms which ex- 

 ercise a reflex control on posture. 



Emetic Drugs 



Proneness to vomiting has been tested by 

 the use of drugs which reproduce many of 

 the symptoms of motion siclmess (16, 35). 

 Results of the administration of such drugs, 

 e.g., neostigmine and apomorphine, to men 

 highly susceptible to seasickness were com- 

 pared with results on a random group of 

 men (16). One of the drugs, neostigmine, 

 did not differentiate the groups, although a 

 significantly greater number of symptoms 

 was displayed by the susceptible men in 

 response to apomorphine. The difference 

 was not so great as to suggest that suscep- 

 tibility to motion sickness is simply a reflec- 

 tion of the "threshold" of the vomiting 

 center or its inhibition. In view of the 

 small number of cases, the findings must 

 be regarded as only suggestive. Further- 

 more, in the particular group studied, the 

 somewhat greater disposition to display 

 symptoms in response to the drug may not 

 have existed as an original predisposing fac- 

 tor and may have resulted from experience 

 with seasickness (16). 



A cdimatization 



Attempts have been made to raise the 

 "threshold" to motion sickness by slightly 

 increasing the duration of a swing test each 

 day for a week or more. In this manner, 

 it is possible to render persons more resistant 

 to the motion of a swing so that they can 

 tolerate longer periods of swinging without 

 the appearance of symptoms (70, 79). The 

 significant issue, however, is the amount 

 and duration of transfer that occurs between 

 such adaptation to a swing and the motion 

 of a ship or an airplane. The literature re- 

 viewed by Mclntyre gives little evidence of 

 transfer of adaptation on a swing to the 

 motion of airplanes or ships (79) . Further- 

 more, the adaptation to the swings them- 

 selves is transitory, lasting perhaps a week. 

 Also relevant is a report of an attempt at 



