ELECTRIC THRESHOLD OF THE HUMAN EYE, ASDETERMINED BY STIMULATION WITH THESINUSOIDAL ALTERNATING CURRENT, AND ITS DEPENDENCE UPONILLUMINATION

A systematic study on the electric stimulation of the eye by the sinusoidal alternating current was made by means of the electronic rheotome within a wide range of frequencies extending from 2 to 1, 000 c.p.s. under the various levels of illumination.1) The threshold strength-frequency curve for the dark adapted eye has at least two main minima in the vicinity of 7 and 30 c.p.s., while the curve for the light-adapted eye has a distinct minimum at about 20 c.p.s. There exists always an abrupt inflection of the strength-frequency curve at around 100 c.p.s.2) The shape of the threshold strength-illumination curve depends complicatedly upon the frequency of a.c. According to the curves' shape, all curves obtained were classified into four types, each corresponding to four ranges of frequency of 2-9, 9-25, 25-50 and 50-1, 000 c.p.s. respectively in approximateestimation.3) It was especially noted that the electric threshold for the frequency around 3 c.p.s. varies in a qualitatively parallel relation to the threshold for an adaequate stimulus with increase in illumination, and that the subjective sensation evoked by such low frequencies is also most alike to the sensation evoked by an adaequate stimulus, and that if the higher frequency is used for stimulation, only the onset and cessation of stimulation causes the electrical phosphenes to be perceived.4) It was discussed that the electrical phosphenes evoked by very low frequencies of sine waves seemed to have a close relation to the “on” elements in the retina, whereas those evoked by the higher frequencies, to the “on-off” and “off” elements.