S. W. Kraukov showed, in his experiments, that the visual acuity was influenced by the auditory stimulation, and infered that, by the summation of the excitation in the brain-centr, the excitation of a sensorial sector was increased by the indirect stimulation given through the other sense organs.
In my investigation I tried to prove his hypothesis by showing the influence of light-stimulus upon the differential-threshold of the intensity and pitch of the tone.
Procedure: Wirth's Mothod of “Complete Series” was used. The influence of light-stimulus was deduced out of the deviation of the threshold of N., in which the light was given simultaneously with the standard tone, from that of V., in which the light was given simultaneously with the variable tone.
If light-stimulus, as Kravkov says, intensifies the tone phenomenally, the threshold of N. may shift upwards while that of V. downwards. So D (Sn.-Sv.)>0 (Sn. and Sv. are the points of subjective equality of cases N. and V. respectively.) On the contrary,if light-stimulus weakens the tone, D<O.
Tones:474 d. v. or 800 d. v., 3.5-4.5 phon for the intensity threshold. 992-1008 d. v.,4 phon for the pitch threshold. Two tones were given successively for somparison, their durations and interval being 1 second respectively.
As light-stimulus, the change of light (usually 5-200 watt) was used.
Apparatus: Vacuum-tube Oscillator for tone-marking. The light was given hrough a small window (usually 1×1cm square) of a box (100×75×75cm) vith the electric lamps attached inside.
Subjects: 22 members and students of our institute.
Results: 1) Light-stimulus intensifies the tone phenomenally when the change f light is 5-200W. (See Tab. V. Fig. 2, 3 in Japanese text p. 258)
2) Such influence of light is smaller, when the window is large. (4×4 cm, 6 x 16cm). (Tab. VII-XI in p.260-261)
3) The influence of light is smaller, when the entire field of vision is illuminated.
4) The degree of the Influence increases as the degree of the change of light tcreases. (Tab. XII, XIII in p. 262)
5) When the starting point of light-stimulus does not coincide with the tone; the influence is very small, while the influence is great even when light-stimulus is given only for 1/3 second, if its starting point coincides with that of the tone. (Fig. 5., Tab, XIV, XVI, in p. 263-265)
From this fact, the dynamical process, caused in the optical sector at the moment when light-stimulus is given, may be said to be more effective to increase the intensity of the tone phenomenally than the quasi-stationary process which follows the dynamical one.
6) The tone is weakened phenomenally when the light changes from 200 w to 5w. (Tab. XVIII, Fig. 7 in p. 266)
7) From the deviation of the threshold of pitch,we maysay thatl ight-stimulus makes the tone appear higher. (Tab. XXI, Fig. 8 in p. 268)
As above mentioned, the light influences in two different ways upon the intensity of tone on one hand and upon the pitch on the other . This may be due to the context of the series of tones in, each case.
