280 Introduction to Anatomy & Physiology Hearing aids amplify and change sounds so that the wearer can better hear the sounds. Some hearing aids amplify all sounds others specifically boost low- or high-frequency sounds. For elderly individuals with hearing deficits, use of a hearing aid not only improves hearing, but also improves the ability to balance. Scientists are studying this recently discovered phenomenon to try to understand the mechanism by which it works. Hearing aids are available in a variety of styles and sizes (Figure 7.16), and price varies considerably. This is why you would want to carefully analyze all information (from healthcare workers and promotional materials) before making inferences about the best products and services for you or the person you are helping with the purchase. “In-the-canal” hearing aids are custom- molded to fit inside the auditory canal. This type of hearing aid is recommended for mild to moderate hearing loss. “Half-shell” hearing aids are custom-fit to sit inside the small, inner bowl-shaped area of the outer ear. These hearing aids are recommended for mild to moderately severe hearing loss. Somewhat larger hearing aids, called “in-the-ear” aids, are custom-designed to fill most of the bowl of the outer ear. This type of hearing aid is recommended for mild to severe hearing loss. Finally, “behind-the-ear” hearing aids, designed to “ride” behind the ear, are capable of greater amplification than the other types of hearing aids. This model, which transmits amplified sound to a molded piece inside the auditory canal, is appropriate for most types of hearing loss. Deafness Deafness is the term applied to any loss of hearing, ranging from a slight to a complete inability to hear. Injuries that affect the structures of the middle or inner ear can cause deafness. Regular exposure to extremely loud sounds such as construction noise or loud music can damage the hair receptor cells in the organ of Corti, leading to hearing loss. Other causes of deafness include excessive earwax, scarring of the tympanic membrane following inflammation, and damage to the auditory nerve or auditory region of the brain. There are two distinct types of deafness: conductive and sensorineural. In conductive hearing loss, the transfer of sound waves from the outer ear through the tympanic membrane to the middle ear is disrupted. The source of the disruption may be fluid or an abnormal growth of tissue or bone. Sensorineural hearing loss occurs when the cochlea fails to send a signal to the brain. Presbycusis (prehz-bih-KYOO-sis) is the term for age-related hearing loss. High-pitched sounds, in particular, become harder to hear as people age. This can make words harder to understand, because consonants, such as b, d, p, and t, tend to be high-pitched during normal speech. When these sounds drop out it can make speech difficult to follow. To speak to someone with presbycusis, it is best to articulate words very clearly rather than to just speak loudly. Presbycusis usually can be improved through the use of hearing aids. Oksix/Shutterstock.com, Jiri Hera/Shutterstock.com Figure 7.16 Hearing aid models. A—“Behind-the-ear” model. B—“In-the-canal” model. A B Copyright Goodheart-Willcox Co., Inc.