386 



MOTION SICKNESS, I 



the cabin after flight can result in a remark- 

 ably lower incidence of first flight sickness. 

 Dissemination of facts about motion sick- 

 ness in pamphlet form may improve the 

 general attitude of service personnel toward 

 motion sickness so that it may become re- 

 garded as an essentially normal process. 

 The desired result would be to have the sus- 

 ceptible person looked upon merely as dif- 

 fering in degree in the same manner as visual 

 or auditory acuity or even stature, and not 

 as "weak" or "queer." 



Engineering Design 



From the point of view of controlling 

 motion sickness alone, few principles of de- 

 sign can as yet be stated, although, in gen- 

 eral, the larger the vehicle the lower the 

 periodic accelerations. Another complicat- 

 ing factor is high speed, which decreases the 

 interval between accelerations and decelera- 

 tions and also increases the peak amplitude. 

 Speed is also important by reason of associ- 

 ated sudden starts and stops and by its re- 

 lation to a rough traveling medium. 



Increase in size, arrangement of seating 

 at the center of gravity, or rotation and 

 provision for viewing of the horizon are 

 factors that might be utilized in reducing 

 motion sickness. Placement of seating and 

 arrangement of windows in vehicles may 

 have an important effect on motion sickness, 

 since informal interviews with persons highly 

 susceptible to motion sickness indicate that 

 motion sickness occurs more frequently in 

 the rear seats of automobiles than in the 

 front and is greatest for the rear seats of 

 limousine-type vehicles. In many instances, 

 it is impossible to permit seating at the cen- 

 ter of rotation and also vision of the horizon, 

 e.g., aboard ships and airplanes. The use- 

 fulness of an artifical horizon for such con- 

 ditions should be studied. 



Control of Auxiliary Factors 



Significant reductions in the incidence of 

 motion sickness can be made by proper con- 

 trol of some of the auxiliary factors attending 

 the exposure to periodic motion. The most 



important of these factors appear to be vision 

 and head position. The latter is, in a sense, 

 a primary factor since it determines the 

 direction of the accelerations imparted to the 

 vestibular apparatus ; in the present context, 

 however, it is convenient to discuss it as an 

 auxiliary factor. 



Vision 



The critical factor in vision appears to be 

 the orientation supplied by viewing the sta- 

 ble environment, e.g., the horizon or land- 

 scape. There are three general conditions 

 of visual orientation which have been studied 

 concomittantly with exposure to motion: (1) 

 eyes open viewing the stable environment, 

 (2) eyes closed, and (3) eyes open, vision 

 restricted to the moving environment, e.g., 

 eyes open below deck or eyes open in a 

 covered swing. The incidence of motion 

 sickness appears to be lowest under condition 

 (1) and greatest under condition (3). Blind- 

 folding subjects increases motion sickness 

 on a swing. When a swing is enclosed with 

 a "cabin" and the subjects keep their eyes 

 open, a further increase is noted (71, 79). 

 These results do not agree with those of 

 Spiegel (106) who reported that viewing a 

 light in the moving environment reduced 

 motion sickness induced by rotational accel- 

 erations. The difference in type of accelera- 

 tion may account for the apparent disagree- 

 ment. Further work should be directed at 

 analyzing this issue. 



The importance of inhibition of motion 

 sickness through visual orientation is re- 

 vealed by the data of Tyler (111). His 

 studies compared the incidence of motion 

 sicloiess in men standing in landing craft 

 viewing the horizon, with men crouching 

 below the gunwales so that they could not 

 see the horizon or other ships; head position 

 was comparable.- In the visually "ori- 



^ Although head position was comparable, free 

 movement of the head was more difficult in the 

 crouching position. Should acceleration in one 

 plane be important, this difference in free head 

 movement may have some relation to the dif- 

 ference in incidence of motion sickness noted by 

 Tyler. 



