Next-generation hearing prosthetics

t is reported that millions of people are suffering from some kind of hearing impairment [1]. The number is climbing due to the increasing portion of elderly people in the world's population. While hearing loss is usually caused by permanent mechanical damage to the ear, there is no medicine to reverse it, and surgery offers little help. Thus, electronic hearing aids or pros-thetics are, so far, the best solutions that patients can rely on. Conceptually , the hearing aid is no more than an amplifier, collecting and amplifying environmental sounds in order to compensate for hearing loss. However, the hearing process is much too complex to be compensated by current hearing aids. Hearing is, by its nature, an intelligent process; people try to understand received sounds, which means that the brain is involved in the process. This nature makes the design of a hearing aid much more complicated than finding a set of linear amplifiers. Current hearing devices employ a set of band-pass filters with different gains. The number of filters in a specific hearing aid may vary, ranging from two to eight. The central frequencies of these filters are usually set at 250 Hz, 500 Hz, 750 Hz, 1 kHz, 1.5 kHz, 2 kHz, 3 kHz, and 4kHz, covering the audible frequency of the human ear. The gains at these frequencies are programmable and set according to the specific needs of a patient. First, a standard clinical procedure is followed to measure the audiogram of the patient, which is normally the hearing loss at five frequencies: 250 Hz, 500 Hz, 1 kHz, 2 kHz, and 4 kHz. Then, based on how much gain the patient needs in order to compensate for hearing loss at the above seven frequencies, a target is generated. Finally, the target is programmed into the hearing aid, on which the patient is asked to undergo some tests under different sound situations. Since the initial target is generated on a formulated basis , it might not fit a specific patient perfectly. A fine-tuning process is, thus, necessary. Two critical steps can be identified from the above descriptions: mapping the audiogram into the target (target generation) and fine-tuning of the target [2]. The mapping of the audiogram into the target is a process to preselect the required gains of the hearing aid for the user. It is desirable to make this first guess as close to the …