404 



MOTION SICKNESS, II 



Three subsequent studies — all in substantial 

 accord — have considered in greater detail 

 the relation between kno\\Ti motions and the 

 direct frequency response in the nerve 

 fibers coming from the cristae (of a horizon- 

 tal canal) : Ross (30) on the frog, Lowenstein 

 and Sand (16) on the ray, and Adrian (1) 

 on the cat. It seems legitimate to assume 

 that their general observations will also 

 apply to man. Taking Lowenstein and 

 Sand's results as representative, one may 

 conclude that: (a) There is, under static 

 conditions, a steady frequency of response 

 from the crista, (b) On deflection to one 

 side the frequency increases, and on de- 

 flection to the other side the frequency 

 decreases.* (c) Over a matter of 20 to 30 

 seconds, at least, "adaptation" — i.e., a 

 decay with time, of the frequency response 

 when the deflection is held constant — is 

 negligible." (d) To a fairly good degree of 

 approximation^ the percent change in the 

 frequency is proportional to the angle of 

 deflection (23). These are all facts of which 

 use will be made presently. 



The nerve response of the sacculus and 

 utriculus has not been studied so widely. 

 Adrian (1), using a considerably more in- 

 direct (but necessarily so, for dissection is 

 much more difficult in the cat) procedure, 

 has reported response curves of the sacculus 

 in which the frequency of discharge appears 

 to rise slightly faster than linearly with angle 

 of static inclinations of the head (for angles 



' This was an unequivocal result in the Lowen- 

 stein and Sand experiments; the existence of a 

 two-directional sensitivity was problematical in 

 Adrian's work, and absent in Steinhausen's. In 

 Mowrer's work on the pigeon (to be cited below) 

 there was again evidence that a receptor on one 

 side was sensitive to rotation in both directions. 



^ Jonason and his co-workers (14) have re- 

 ported an interesting effect on guinea pigs of much 

 more prolonged stimulation, viz., degenerative 

 changes in the labyrinth as a result of exposure to 

 angular accelerations of 39.4° per sec.^ for 100-200 

 hrs. 



^ The approximation here involved is, in all 

 probability, that the angle of deflection must be 

 small (say, less than 25°). 



from 0°-40°). This curvature is in the 

 opposite direction from that which would 

 result from a simple geometric factor (sine 

 of the angle of inclination), and therefore 

 probably represents a true non-linearity in 

 the response. As in the case of the canals, 

 however, the response shows little adapta- 

 tion. From experiments in which the ani- 

 mal's head was accelerated up and down, 

 Adrian concluded that acceleration down- 

 ward probably stimulated the utriculi (whose 

 otoliths under these conditions would be 

 pulled away from their maculae) . Acceler- 

 ations upward probably stimulated the dor- 

 sal lobes (which face downward) of the 

 sacculi for the same reasons. Accelerations 

 sideways probably stimulate the sacculi, and 

 do so asymmetrically (12, 15), that is, only 

 on one side of the head is the otolith pulled 

 away from the maculae. 



In the case of the sacculus and utriculus 

 there is no indication, as there is in the 

 canals, that a single macula responds to 

 acceleration in both directions normal to 

 itself, but instead that it reacts only when 

 the otolith is pulled away from it (see, how- 

 ever, the interpretation of swing experi- 

 ments discussed below). 



To test quantitatively a hypothesis about 

 the mode of action of the labyrinthine recep- 

 tors requires first an analytic formulation 

 of the hypothesis. Such a formulation, 

 once justified experimentally, is useful in 

 diverse ways to be indicated presently. 



Information of the proper sort to test 

 hypotheses about the sacculus and utriculus 

 is so meager that formulations of the action 

 of these receptors must remain for the time 

 being purely speculative. We shall here 

 merely note that if the otolithic system de- 

 flects like a damped vibrator, and that if 

 one restricts the problem to deflections 

 small enough so that the afferent nerve fiber 

 frequency, v, is proportional to the deflec- 

 tion, then V satisfies the equation, 



u -f 2X^ -t- /cV = m (3)| 



where 2X and k^ are numbers proportional 



