発生電位による振動感覚の計量化について

抄録

The evaluation of vibratory sensibility should be performed by a physical measurement which also relates to the subjective evaluation. It is necessary to find a new method of phsical measurement. This paper presents psychological and physical experiments carried out by using a vibrometer as an acoustical calibration apparatus. The vibration threshold value measurements of were made using sine waves of 30-700 Hz triangular, and saw-toothed waves of 30-300 Hz and square waves of 30-80 Hz. Ten test subjects were kept seated. A portion (about 80 mm^2) of the vibrator is in contact with the skin. The Square wave has a difference of 7, 9 dB at 80 Hz and the difference becomes 12. 3 dB at a lower frequency (30Hz) as compared with a sine wave. This has also been proved physiologically by the impulse rate of a stimulus given directly to the tactile receptor; it implies that a steeper stimulus has a higher threshold value. In the present paper the quantification of vibratory sensitivity is attempted, and it is shown that a potential variation of a few μV can be picked up by applying vibratory stimulus to the skin, which at the same time is used as reference signal to a lock-in amplifier, and detecting the same frequency components of electric signal generated from a living body by the stimulus, and that cutaneous sensetion can be therefore quantified as a small amount of potential variation. In order to observe the corresponding electric signal, the subjects were placed inside a shielded room and provided with Ag-AgCl electrodes at two points on their skin. In the measurements, the calibration of the electric signal observation portion was made with a 10μV sine-wave input, and that of the final detection part with a cathode-ray oscilloscope and a photocoder Owing to the size and shape of the electrodes, they were placed around the wrist of the subjects. The two electrodes were spaced apart at 50 mm, but variation of the separation at 30-40 mm exerted no effect on the electric signal. A curve was plotted by taking the stimulus level on the horizontal axis and the potential variation or strengh evaluation on the vertical axis, then it was found that there is nearly a linear relation. Furthermore in the experiment was measured the generating potential of each finger to which vibratory stimulus was added. The generating potential and the vibration threshold value are different according to the subject, but the tendency is almost same. The subject who shows a high potential has a low vibration threshold value, and the subject who shows a low potential has a high vibration threshold value. The results obtained from the experiments are as follows: (1) Vibratory sensation can be quantified as generating potential in the living body, though it has so far been measured only psychologically. (2) It may be possible to acquire more information by using square, triangular and saw-toothed waves than just a sine wave. (3) Exponent n involved in the Stevens' power law may be put as 1 for the vibratory sersation and constant k may be put as 0. 25 to 1. 4 at 40 to 200 Hz. (4) Each finger shows a remarkable potential variation at low frequencies and little vaiation at high frequencies. This paper deals with vibratory sensation only. It is a matter of course that it should be attempted to quantify other sensations.