# Omnidirectional Haptic Guidance for the Hearing Impaired to Track Sound Sources
## 1 Introduction
The subject learns the pattern of the tactile stimuli and makes a correspondence to the acoustic environment. With a certain amount of training, it is possible not only to localize a sound source but also to track and selectively pay attention to it. On the other hand, no robot can act like a hearing dog, but many elemental technologies have been proposed to realize the function of assisting a disabled person after determining their acoustic environment. Many studies have been reported on the use of microphone array systems for sound source localization, estimation of the trajectory of moving sound sources, and sound source tracking [14, 15, 16]. A microphone array system consists of many microphones placed far apart, which makes the overall size of the array unsuitable for mobile platforms and places a heavy computational load on the computer. [PERSON] et al. listed the following four constraints that are required for mobile platforms [17]: (1) geometric constraints: there must be a trade-off between the combined size of all sensors and the performance of the platform in motion; (2) real-time constraints: short processing time should be guaranteed; (3) wide frequency bands: the computer must be able to process at high speed; and (4) environmental constraints: they must be operable in dynamic and unpredictable environments. Microphone array systems violate constraints 1, 2, and 3. Acoustic processing using binaural microphones that can be easily mounted on a mobile platform and at least satisfy constraint 1 is known, and there are many reports on sound source localization, detection of multiple sound sources, and tracking of moving sound sources [17, 18, 19, 20, 21, 22, 23, 24]. By mounting the microphones on a mobile platform, their orientation can change. This is used for acoustic processing in active audition [18]. In this study, we used an ear microphone that is easy to wear and to fix. When a hearing-impaired person wearing an ear microphone moves his or her head, the direction of the microphone changes. Active audition is often installed in moving robots, and tracking of moving sound sources by robots has been reported [24]. An algorithm should be adopted that satisfies all of the above constraints among the algorithms that use such computers to localize and track moving sound sources. Let us assume that the location of the sound source can be estimated by a computer. Then, how can we convey this information to someone who is hearing impaired? Various methods of presenting the information have been proposed [25, 26, 27, 28, 29, 30, 31, 32]. Presenting information on a cell phone screen is the easiest and most convenient way. However, visual communication is not appropriate as a human-machine interface in this case because hearing-impaired people use their vision to understand their surroundings. [PERSON] et al. (2000) proposed a method of using a 3 \(\times\) 3 array of vibrators on a visually impaired person's back to indicate the direction of walking by changing the waving pattern [26]. Nine vibrators are heavy, and it is difficult to gather all of them close together. A tactile display using piezoelectric elements was developed [27], [PERSON] et al. proposed a soft tactile actuator that can be assembled [31], and Ontenna, a hearing aid for the deaf, is a hairpin-type device that can convert sound intensity into light or vibration intensity [32]. Haptic interfaces are also used in visual aids for the visually impaired [33, 34, 35, 36, 37, 38]. In addition to skin stimulation by physical vibration, electrical stimulation of muscles has been proposed as a tactile stimulus [33]. There are proposals to show walking routes to visually impaired persons while avoiding obstacles in the road detected by ultrasonic sensors and to give instructions for a walking route by referring to GPS location information and a map [36, 37, 38].