# Bone Conduction Auditory Navigation Device for Blind People
## 1 Introduction  
As of 2015, approximately 36 million people were reported to be blind, 217 million people were reported to have moderate to severe visual impairment, and 189 million people were reported to have mild visual impairment [1]. Furthermore, according to the WHO (World Health Organization), in 2019, 2.2 billion people were reported to be visually impaired or blind, and the number of visually impaired people was reported to be increasing [2]. As indicated by these reports, the number of people with visual information impairment is expected to continue to increase. These people do not have access to information from sight and, therefore, need to rely on information from senses other than sight while moving through the city. The safety of walking for such individuals is secured through the use of white canes and various types of sound information. A visually challenged person perceives the environmental situation using information obtained from sensory organs other than the eyes in all cases, but, especially, when walking in the city, the individual uses information obtained from the auditory and tactile senses. Tactile information is mainly obtained through a white cane and from the unevenness of the ground through the soles of the feet, whereas auditory information is mainly obtained from sounds of approaching cars and other moving objects, footsteps of others, and signal sounds in public spaces. The type of object or its relative position may be determined from the sound, whereas in cases related to human echolocation, the existence of an object is recognized by the sound reflected from obstacles, such as walls [3, 4]. According to [PERSON] et al. [4], humans have been found to use echoes to detect objects. As for the sense of the directionality of objects, [PERSON] and [PERSON] [5] showed that blind people are more sensitive to binaural sound localization than sighted people. As mentionedabove, visually impaired people indirectly detect morphological characteristics in their surrounding environment based on information of sounds in their environment. In such a situation, various technologies have been proposed to increase the mobility of visually impaired people. Electronic aids for the mobility problems of blind people have been investigated since the 1960s [6]. [PERSON] et al. investigated a new system that assists blind users in orientating themselves in indoor environments [7]. [PERSON] et al. then presented a new blind navigation system [8] for traveling in a city using an RFID (Radio Frequency Identification) tag and wireless and mobile communication. [PERSON] et al. newly developed the nav4b system, which combines guidance and navigation with object recognition by extending the traditional aids of the white cane and a smartphone [9]. [PERSON] et al. presented a new electronic travel aid \"acoustic prototype\" using a binaural reproduction technology [10] with air-borne sound. In contrast, [PERSON] et al. proposed an obstacle detection and warning system by bone-conduction acoustic feedback to assist visually impaired persons [11]. In recent years, bone-conducted sound technology has been used in various fields. An implantable bone-conducting hearing aid device [12] for people with conductive hearing loss due to damage to the ear canal or middle ear system has been broadly used. On the other hand, this technology has also been widely used in various industries, targeting people, including not only hearing-impaired people, but also healthy people. For example, such systems are used as a communication devices in noisy workplaces [13]. Bone-conducted sound is transmitted via different sound transmission paths as compared to air-borne sound. Since we can acquire information by bone-conducted sounds while also hearing environmental sounds, this system can be applied to the guidance of visually impaired people in the city. [PERSON] and [PERSON] studied the navigation performance with bone-conducted sounds inside a virtual environment [14].