# Omnidirectional Haptic Guidance for the Hearing Impaired to Track Sound Sources
## 1 Introduction  
We use our five senses to grasp our surroundings, and it is said that vision accounts for about 90% of the information we receive. However, it is thought that people use auditory information to compensate for information that cannot be confirmed visually because it is hidden to the side, behind, or in the shadows. For example, when we cross a road at dusk or at night, when visibility is limited, and a stopped vehicle suddenly moves or turns at an intersection and suddenly comes into view, visual information alone is not enough to quickly detect it; auditory information is also required. When crossing the road, we often unconsciously turn our head in the direction of the sound of the vehicle. Due to the anxiety caused by auditory information alone, we may turn our face to reconfirm the sound source visually. On the other hand, hearing-impaired (deaf) people and young people who walk around with earphones listening to music at high volume may not be able to hear the sounds around them, which is assumed to increase the risk of experiencing traffic accidents. Hearing dogs play a role in supporting the daily lives of the hearing impaired. Indoors, they listen to various sounds such as ringing telephones, doorbells, boiling kettles, fire alarms, and human voices on behalf of hearing-impaired people; communicate what the sounds are; and lead them to respond appropriately. A hearing dog does not convey detailed information about the sound source but merely attracts the person's attention through direct contact or special behavior. It is assumed that the hearing-impaired person, given simple information by the dog, knows what action to take after visually confirming the situation. In this study, we focus on auditory support for the hearing impaired to cross roads safely. The purpose of this study was to develop a hearing assistance system that can detect the location of vehicles on roads and to present it to people. In order to confirm that avehicle is approaching on the road, it is necessary to continuously track the position of the sound source. If we can develop a hearing assistance system that detects sounds with a microphone, identifies the sound source, and notifies the user of its location, we can improve the quality of life for the hearing impaired. Some basic ideas and technologies related to this system are described below. Devices that convert sound characteristics into patterns of vibrating tactile stimuli have been proposed as a way for the hearing impaired to understand their acoustic environment [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. In pioneering work in this field, [PERSON] (1955, 1959) created two artificial cochleae and fixed them to a subject's forearms [1, 2]. The sound generated by loudspeakers drove two spatially separated microphones, in which the output was amplified to operate the two artificial cochleae, which vibrated on the subject's arms. As a result, the subject was able to accurately determine the direction of the sound. [PERSON] reported that auditory sound source localization depends only on the difference in intensity of sounds. [PERSON] et al. (1979) reported that, by transmitting sound information through vibration on the skin, subjects can estimate the distance to and direction of the sound source at the same time [4]. They supported [PERSON]'s claim by pointing out that sound localization by vibration based on differences in intensity is better than that based on phase or time differences. [PERSON] et al. (1976) showed that tactile localization of a sound source is possible with accuracy comparable to that of normal hearing, that a moving sound source can be tracked, and that attention can be selectively directed by tactile sensation [5]. It has also been reported that people with cochlear implants can track moving sound sources [6]. The distance and direction to the sound source, which are higher-order information from the perceived tactile stimuli, are left to the subject's own judgment.