Abstract
There are many papers on vibratory sensation for vibrations perpendicular to the skin but only a few papers on vibratory sensation for vibrations parallel to the skin. In one of them, it is mentioned that parallel vibrations are better than perpendicular vibrations as a means of information transmission. The reasons are, however, not clear why the difference in sensations for two vibration modes occur.
Parallel vibratory sensations are studied in order to 1) make the difference of sensory characteristics clear between vibration parallel to and vibration perpendicular to the skin, 2) grasp the effect of contact force of stimulator on a threshold curve and 3) estimate the channel capacity in information transmission via amplitude modulated stimuli.
Experiments were carried out by a method of conductor adjustment in a noise-free room with auditory masking by random sound from a headphone and with a stabilizing plate around the stimulator in order to localize vibration on the skin.
The results showed that threshold-frequency characteristics are similar to those of perpendicular vibration except that at around 20 Hz, curves are concave because of the mechanoreceptors which are sensitive to skin stretching. The effect of the contact force on the threshold curves is considered slight. The channel capacities estimated from just noticeable difference are 2. 3 bits to 3. 9 bits for subject K and 5. 2 bits for subject S.
