Abstract
The deaf may be exposed to a number of dangers in his daily life when he cannot notice a voice of warning or the approaching sound of a car from behind or out of his visible range. Nevertheless, there is scarcely any attempt to develop a prosthetic sound localizer via his remaining tactile or visual sense to assist him. The authors tried to find a practical method for a tactual localizer of sound for the deaf. It is reported that two channel vibratory stimuli presented to each of two points on the surface of the skin cause a phantom sensation between these two stimulated points. Based on this phantom sensation, we have tried to substitute auditory sound localization by corresponding the position of the tactile phantom sensation with the direction of a sound source. First of all, we compared the tactile sense with the auditory sense by means of psychophysical techniques (Fig. 1). As the result, the phantom sensation by intensity defference between two channels was similar to the auditory lateralization, however in regard to the time difference, it was much inferior in comparison to that of the auditory system (Figs. 3, 4, 5, and 6). It is also reported that the auditory sense localizes a sound source by the intensity difference between the sounds received by right and left ears for the higher tones with the frequencies more than 1000〜1500 Hz, while for lower tones, by time difference, as the intensity deifference is very little for lower frequency tones. On the other hand, a car noise or a voice subject to the localization in our daily life has relatively higher energy in the range of lower frequencies than 500〜1000 Hz. Hence, it seemed necessary to transform the time defference of the lower sound into intensity defference to obtain better tactile recognition of sound localization. Considering these characteristics of the tactile sense and other conditions, we designed a time intensity converter (Fig. 7, 8, 9, and 10). Using our tactual sound localizer with this converter, a subject who was equipped with a pair of vibrators 4〜20 cm apart on the skin sueface of hand, abdomen, breast, or back could detect the approaching direction of a car with a velocity of 20 km/h and its movement from rihgt to left. Problems of localization of multiple sound sources and approximate distinction of sound have not been solved. We are trying to find new techniques for these problems.
