Hearing aids-external electronic devices used to help individuals with hearing loss-traditionally consist of a microphone, an analog-to-digital converter, a digital signal processor, a digital-to-analog converter, and a receiver that delivers an acoustic signal into the external auditory canal. In 2008, 97% of all hearing aids sold used digital processing. Catherine V. Palmer, PhD, provides a review of current digital hearing aids.
Explore this issue:December 2009
Children are now being fitted with hearing aids by the age of 6 months due to successful early identification of hearing loss and new screening guidelines. Adult amplification recommendations are based on hearing evaluations and patients’ reported difficulties.
The choice of a hearing aid depends on a number of factors, including degree of hearing loss, site of lesion, ear shape and size, desired battery life, and patient preference. Behind-the-ear (BTE) hearing aids are attached to an earmold that couples the hearing aid to the ear canal. Other hearing aids can be in the ear (ITE) and in the canal (ITC) or completely in the canal (CIC). The newest style consists of a mini-BTE coupled to the ear with slim tubing ending in a small dome, leaving the ear canal open. The new styles can also make the distinction between having the receiver cased in the BTE or at the end of the sound channel (the slim tubing). Having the receiver in the canal allows for a smaller BTE case without loss of amplification; however, the receiver is more exposed to moisture, heat, and cerumen in the ear canal.
The basic goals of a hearing aid fitting are to provide audibility for the range of sounds encountered in daily life, to allow the listener to hear in complex (noisy) situations commonly occurring in daily communication, and to be comfortable acoustically and physically. Audibility is obtained for soft, moderate, and loud inputs without the need for constant volume manipulation through the use of compression and increased bandwidth. Directional microphones assist in hearing through noise. New developments have also been introduced in assistive listening devices and feedback management.
Constantly developing technology requires continual modifications to hearing aid technology as well. Hearing aids must be compatible with other listening devices that patients use, such as telephones, mobile phones, and music players. Datalogging and datalearning are helpful in fine-tuning the devices to suit the user.
Although hearing aids are moving toward consumer electronics-as opposed to medical devices-in looks and features, they are different from consumer electronics in that they much meet the needs of individuals with wide variations in hearing ability and must process constantly varying signals, whereas consumer electronics are designed for uniform hearing and one type of signal. Another challenge is the development of adequate rechargeable batteries for hearing aids.