Hearing

Lore & Background

Sound may be heard through solid, liquid, or gaseous matter. It is one of the traditional five senses. Partial or total inability to hear is called hearing loss. In humans and other vertebrates, hearing is performed primarily by the auditory system: mechanical waves, known as vibrations, are detected by the ear and transduced into nerve impulses that are perceived by the brain (primarily in the temporal lobe). Like touch, audition requires sensitivity to the movement of molecules in the world outside the organism. Both hearing and touch are types of mechanosensation.

Reader's Guide

There are three main components of the human auditory system: the outer ear, the middle ear, and the inner ear. The outer ear includes the pinna and ear canal, terminating at the eardrum. The middle ear contains the ossicles (malleus, incus, stapes) and muscles that protect hearing. The inner ear includes the cochlea and organ of Corti, where hair cells transduce vibrations into nerve impulses. Sound information travels via the auditory nerve to the brainstem, then to the inferior colliculus, medial geniculate nucleus, and primary auditory cortex. Hearing can be measured by behavioral tests using an audiometer or electrophysiological tests such as ABR, OAE, and ECochG. Hearing loss types include conductive, sensorineural, and mixed. Degrees range from mild (25–40 dB HL) to profound (95 dB HL or more). Causes include heredity, congenital conditions, presbycusis, acquired factors, noise-induced hearing loss, ototoxic drugs and chemicals, and infection. Prevention involves hearing protection devices and environmental modifications. Management includes hearing aids and cochlear implants. Hearing loss is associated with Alzheimer's disease, dementia, and type 2 diabetes. Hearing threshold and localization are reduced underwater in humans but not in aquatic animals.

Did You Know?

• The three smallest bones in the body—the malleus, incus, and stapes—are located in the middle ear.
• The basilar membrane in the cochlea is tonotopic, with high frequencies at the base and low frequencies at the apex.
• Hearing loss is associated with Alzheimer's disease and dementia, with greater hearing loss tied to a higher risk.

Notable Quotes (Wikiquote)

"He ne'er presumed to make an error clearer;—In short, there never was a better hearer." — Hearing "Lord Byron, Don Juan (1818-24), Canto XIV, Stanza 37." — Hearing "George Herbert, Jacula Prudentum (1651)." — Hearing "Who is so deaf as he that will not hear?" — Hearing