Symposium on the Role of the Vestibular Organs in Space Exploration (1970) / Chapter Skim
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THE OTOLITH ORGANS AS A PRIMARY ETIOLOGICAL FACTOR IN MOTION SICKNESS
THE OTOLITH ORGANS AS A PRIMARY ETIOLOGICAL FACTOR IN MOTION SICKNESS
Pages 53-68
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From page 53... ...
The shifting emphasis on the essentiality of the two organs is briefly traced, leaving in doubt today the role of the otolith organs formerly regarded as essential in the causation of seasickness and airsickness. This doubt has arisen by the demonstration that nystagmus, easily evoked when the canals are stimulated by angular or Coriolis accelerations, also may be manifested when a person is exposed to rectilinear accelerations or to "rotating linear acceleration vectors" (RLAV)
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From page 54... ...
Thus, when motion sickness was experienced under mild sea conditions, the linear accelerations were above threshold value while the angular accelerations were below 2 to 4 deg/ sec/sec which was then regarded as in the threshold range. Moreover, clinical observations revealed the absence of nystagmus, which was regarded as supporting evidence that the semicircular canals were either not implicated or, if they were, played a small etiological role.
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From page 55... ...
If the canals were stimulated at the lower effective stimulus level, the rotating linear acceleration vector evoking symptoms would represent a second fairly efficient stimulus mechanism, inasmuch as the accelerative forces involved were small. If the canals were not stimulated, the question of the significance of their resting discharge arises and whether it was modulated by the unusual input from the otolithic receptors, and, in this way, would give rise to symptoms.
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From page 56... ...
Interpretation of the findings is made difficult because of the great individual variance in susceptibility to motion sickness and in ocular counterrolling values among clinically normal persons. The first subject was "discovered" fortuitously, during a demonstration in the slow rotation room (SRR)
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From page 57... ...
Inasmuch as parabolic flight exclusive of the weightless phase may properly be regarded as a force environment tending to evoke motion sickness, the reduced susceptibility manifested by some subjects during the test procedures was regarded as a conservative valid finding, while increased susceptibility would have to be interpreted with caution. The further demonstration, however, that six subjects experienced symptoms 130 en BO 2 90 §60 MOTION SICKNESS SUSCEPTIBILITY 0, .1, OKI, FIGURE 1.
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From page 58... ...
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From page 59... ...
-- Motion sickness susceptibility in zero g. Effect among six susceptible subjects of active head movements relative to the restrained condition upon motion-sickness susceptibility measured in terms of the number of parabolas required to provoke Malaise III.
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From page 60... ...
The question whether the semicircular canals also are stimulated by a rotating linear acceleration vector has been discussed above. The endpoint used in this series of observations, "moderate malaise" (M II A)
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From page 61... ...
On one occasion all except ZA were exposed for 6 minutes at terminal velocities of 10, 20, and 30 rpm, and all except GU were exposed on other occasions at 30 rpm for periods of 10 minutes or longer. Results Motion Sickness Symptoms of all but 6 of the 66 control subjects reached the endpoint during the "standard" test, and the variance in their susceptibility is shown in figure 4.
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From page 62... ...
. In general, there was a greater tendency for the L-D subjects to become disoriented than was the case for the normal controls, and there were greater individual differences among the L-D subjects in reporting their subjective impressions with regard to their orientation to the gravitational upright and in FIGURE 5.
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From page 63... ...
G M.: Response of Lateral Semicircular Canal Units in Brain Stem to a Rotating Linear Acceleration Vector.
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From page 64... ...
P.; GUEDRY, F E., JR.; AND GRAYBIEL, A.: Effect of Changing the Resultant Linear Acceleration Relative to the Subject on Nystagmus Generated by Angular Acceleration.
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From page 65... ...
If the otolith effect is simply missing as you suggest, then the axis of rotation signaled by the canals during head movements is not in direct conflict with any specific information from the otoliths. In the rotation situations to which I referred in our experiments, head movements produced directional information from both the canals and the otoliths, and the directional information from these two sources was incompatible.
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From page 66... ...
By locating individuals within this hypothetical multifactor space, through appropriate testing, we might be able to predict some individual differences in motion sickness susceptibility. Torok: Autonomic nervous responses to strong vestibular stimulation have been known for a long time.
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From page 67... ...
SESSION III Chairman: THOMAS C
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