THE LIMIT OF THE LABYRINTHINE FUNCTION Introduction of its new concept

Abstract

In the subliminal rotation procedure, the subject is either made to wear glasses of +20 Dor is seated in a rotating chamber in order that influences of visual sense may be excluded as much as possible and that the only labyrinthine function may be observed.However, in combining visual stimulation positively with this procedure, Fukuda et al.found that the subliminal rotation was, in fact, not subliminal since this rotation did promote optic nystagmus and the labyrinthine function was evidently acting as a supporter of optic reflex.According to them, it is unreasonable to consider the so-called minimum angular accerelation as the threshold or the limit of the labyrinthine function.Fukuda insists that the limit of the labyrinthine function should be defined as the angular velocity at which labyrinth can support optic reflex maximally.Based on this view, the writer has carried out following experiments and a new concept regarding the limit of the labyrinthine function was discussed.Experiments were made on rabbits and guinea pigs with dark eyes.I.The subliminal rotation with angular accerelations of 1.0°/sec2 and 0.3°/sec2 was imposed on the animal.A rotating chamber was not used, thus during the rotation, the animal received optokinetic stimuli caused by relative movements of external environment.To apply constant optokinetic stimuli, the animal was placed on a chair situated in a large cylinder with vertical black lines of which details had been reported previously.Should accerelations of 1.0/sec2 and 0.3°/sec2 be really subliminal, nystagmus caused by rotation of the animal with intact vision might be pure optic nystagmus.To inquire into this point the large cylinder was rotated to reverse direction with the same accerelations as above around the animal rested on the chair.The result was that when the chair was rotated jerks of nystagmus were far more frequent as.compared with those in case of rotation of the cylinder.Thus it is apparent that the subliminal rotation does stimulate labyrinth and therefore it is not subliminal in true sense.II.When optic nystagmus was observed applying optokinetic stimulation in passing vertical black lines before animal's eyes, jerks of nystagmus increased in proportion to increase in velocity of the lines.However, if the velocity was increased beyond a critical level jerks of optic nystagmus decreased promptly until at last eyes were rest immobile.In human experiment, the subject could not percept individual black lines in such state but he only saw a vague flow before his eyes.The critical angular velocity which induces maximum jerks will be called ″ the limit in pure optic nystagmus ″.Similar changes of nystagmus were observed in case of subliminal rotation with intact vision, and the frequency of jerks showed a peak at a certain angular velocity.However, this critical velocity, which will be called ″the limit in subliminal rotation with intact vision″, was by far faster than that in pure optic nystagmus in spite of identity of optokinetic stimulation applied.This discrepancy is indeed due to the participation of labyrinth in case of rotation with intact vision.The latter limit, therefore, will deserve being called ″the limit of the labyrinthine function″ in true sense.Further it should be noted that the limit here defined is not an angular accerelation but an angular velocity.