390 



MOTION SICKNESS, I 



of activity. Such results prompt the sug- 

 gestion that MacPhee and Pennington anal- 

 yze their findings in greater detail since they 

 merely reported that "emotional instability" 

 was present in 100 men with a history of 

 motion sicloiess (64). 



A report of the Flying Personnel Research 

 Council of Great Britain on 120 men elimi- 

 nated from duty because of airsickness in- 

 dicated that only 9 cases of neurosis were 

 found and 51 cases of neurotic predisposition 

 (108). In only 19 of the 120 cases of airsick- 

 ness disability was neurotic predisposition 

 thought to play a role. In a group of 30 

 consecutive navigator cadets eliminated for 

 severe airsickness, the "emotional" factor 

 was believed to be predominent in 15 cases 

 (22). The evidence gives support to the 

 general conclusions of Symonds and Williams 

 which may well serve as a summary to this 

 section, with the reader substituting the term 

 "motion siclmess" for "airsickness": "When 

 a man is suspended for airsiclcness at any 

 stage of training, the cause is usually motion 

 sickness uncomplicated by psychological fac- 

 tors. Psychological factors, either neurosis, 

 neurotic predisposition or faulty morale — 

 may contribute by lowering the physiological 

 threshold for tolerance of motion, or by re- 

 ducing the man's ability or willingness to 

 endure symptoms, but psychological factors 

 are seldom of major importance" (108). 



Suggestion 



Suggestion has been thought to play a role 

 in motion sickness in both a positive and 

 negative manner. If one person becomes 

 motion sick aboard ship or in an airplane, 

 presumably others may become sick by wit- 

 nessing the distress of the ill person. Con- 

 versely, however, if one is given a pill with 

 no active ingredient, a placebo, and told it 

 will cure motion sickness, then by suggestion 

 alone amelioration or prevention of symp- 

 toms has been thought to occur. Tyler 

 (111) studied the incidence of motion sick- 

 ness in three groups of personnel: (1) no med- 

 ication, (2) placebo or dummy pill, and (3) 



active drugs. The incidence of motion sick- 

 ness was as great in the placebo group as in 

 the untreated group, whereas the active 

 drugs significantly reduced the incidence. 

 If suggestion were important, the opposite 

 results would have been obtained, i.e., the 

 untreated group would have had a signifi- 

 cantly higher incidence than the placebo 

 group and the active drugs would not have 

 had a significant advantage over the placebo 

 treated group. Tyler's results are especially 

 conclusive, since they are based on several 

 experiments and were conducted by inde- 

 pendent observers under a variety of sea 

 conditions. 



Physiological Factors in Motion 



Sickness 



Three areas of physiological data may be 

 distinguished: (1) conditions of the environ- 

 ment which alter the physiological state of 

 the body and the appearance of motion 

 sickness, (2) the sequence of physiological 

 events involved in motion sickness, and (3) 

 the internal physiological states that are 

 relatively independent of the environment 

 but may affect the susceptibility of the indi- 

 vidual to motion sickness. The latter two 

 areas have been studied by observations on 

 persons before, during, and after motion 

 siclcness and by detailed studies of persons 

 of different degrees of susceptibility in an 

 effort to analyze the physiological basis for 

 individual differences. Such studies have 

 attempted to discover why, in the face of 

 the same pattern of acceleration, one person 

 becomes motion sick while another displays 

 no signs of being ill. An important distinc- 

 tion must be made between those factors 

 which are necessary for the production of 

 motion sickness and those which are not only 

 necessary, but which also determine the rel- 

 ative susceptibility of an individual. Thus, 

 we do not know the contribution of the thres- 

 hold of the vestibular apparatus to individ- 

 ual differences, although we do know that 

 these sense organs are necessary for the ap- 

 pearance of motion sickness. It is con- 



