STUDIES CORRELATING INCIDENCE OF MOTION SICKNESS 



409 



it than when it is pulled away from it. It 

 will be recalled that this is the reverse of 

 Adrian's conclusion. 



Of the many recent large-scale studies 

 summarizing observations on incidence as a 

 function of frequenc}^ and magnitude of 

 stimulation, etc., the author has found it 

 possible to draw physical inferences about 

 the receptor system in only one case, viz., 

 the important series of investigations by 

 Wendt and his associates (2-5 inclusive). 

 In these studies human subjects (Naval 



S.I. = 



2 X (number of) 1 X (number of) 

 (vomit cases) (nausea cases) 



Total number of cases 



X 100. 



Statistical questions of experimental design 

 and interpretation were carefully considered 

 (2), In the following discussion, in addition 

 to symbolism previously introduced, a will 

 denote the acceleration level of an individual 

 pulse, in multiples of g^^, and /3 the duration 

 of an individual pulse, in seconds. 



(2) 



(3) 



(5) 



Fig. 4. Acceleration wave forms used by Wendt et al. The capital letters, A, B, etc., are the code 

 designations used by Wendt; the numbers enclosed in parentheses refer to the bibliography of the 

 present paper; the remaining symbolism is as in the text. In the case of asymmetric waves, the two 

 sickness indices refer to results obtained with the wave as drawn, and with its inverse. 



cadets and student officers) were placed in 

 an elevator-like device, seated with ear eye 

 line horizontal and blindfolded. The verti- 

 cal acceleration imposed had an approxi- 

 mately square wave form, and features of 

 the wave form were varied experimentally 

 in a manner to be described below. Sub- 

 jects were exposed to the motion for 20 

 minutes or until they vomited; of groups of 

 about 100 subjects some 25% generally dis- 

 played either nausea or vomiting. The score 

 employed was the "sickness index," 



Wendt 's composite results are summarized 

 graphically in Fig. 4, where the acceleration 

 wave form appears together with the sickness 

 index which it evoked. His general thesis 

 in these studies appears to have been that 

 the time characteristics of the forcing func- 



'^ In some experiments a was not specified, 

 and the value has then been calculated by the re- 

 viewer from the given changes in velocity and the 

 "duration of the acceleration phase"; obviously 

 such average values may be in error, and are 

 always marked with a bar, thus, a. 



