Citation

Stapp JP. Proc. Am. Assoc. Automot. Med. Annu. Conf. 1962; 6: 160-183.

Copyright

(Copyright © 1962, Association for the Advancement of Automotive Medicine)

DOI

unavailable

PMID

unavailable

Abstract

Subjectively, the first three derivatives of motion can be perceived with qualitative discriminations of magnitude, rate, and duration. Velocity in constant linear motion can be perceived visually in terms of angular displacement relative to other objects. A man sealed in a black box cannot tell constant linear motion from rest, without visual reference of displacement. Constant linear or angular acceleration would be perceptible in such a black box, as pressure on tactile sensory endings and as force displacing viscous-elastic masses of the body. Absence of acceleration by nulling the earth's gravity in orbital space flight would be perceptible in the black box by the lack of tactile and viscous-elastic sensations normal to the one-gravity force of the terrestrial environment. Indeed, the threshold of perception is less than one-twentieth of the earth's gravity environment.

Even in the presence of one G in the normal axis, small transverse accelerations in the horizontal axis -- such as would occur at six-foot radius and eight revolutions per minute on a turntable -- can stimulate the organs of equilibrium associated with the inner ear. Extensive motions of the head in this weak transverse acceleration vector can stimulate these organs to the point of involuntary reflex responses of apprehension, nausea and vertigo. These do not occur with similar head motions in orbital weightlessness, nor in a constant vector of transverse acceleration with the head held still; therefore, change of accelerative force on the organs of equilibrium stimulates the unpleasant reflexes of motion sickness. Thus, the third derivative of motion, or rate of change of acceleration, causes motion sickness.

Rate of change of acceleration of greater magnitude and abruptness is perceived as a jolt, or as vibration in the case of repeated oscillations. Injurious parameters of acceleration and jolt cause damage to structure and function of the living body just as they do to inert materials having comparable physical properties. Living matter has inherent adaptation and self repair up to the irreversible limit of death, although it is made of non-living materials. Indeed, the materials of the human body vary in consistency from the density, rigidity and hardness of dental enamel to the frothy, elastic fragility of lung tissue.