Module 24: Hearing

audition

the sense or act of hearing.

amplitude

the height from peak to trough

frequency

the number of complete wavelengths that pass a point in a given time (for example, per second).

pitch

a tone’s experienced highness or lowness; depends on frequency.

decibels

We measure sound amplitude in decibels, with zero decibels representing the absolute threshold for hearing. Every 10 decibels correspond to a tenfold increase in sound intensity

middle ear

the chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.

ossicles

the three smallest bones in the human body

inner ear

the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

cochlea [KOHK-lee-uh]

a coiled, bony, fluid-filled tube in the inner ear; sound waves traveling through the cochlear fluid trigger nerve impulses.

sensorineural hearing loss

hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerves; the most common form of hearing loss, also called nerve deafness.

conduction hearing loss

a less common form of hearing loss, caused by damage to the mechanical system that conducts sound waves to the cochlea.

cochlear implant

a device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea.

place theory

in hearing, the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated.

frequency theory

in hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. (Also called temporal theory.)

Responding to loud and soft sounds

Our brain interprets loudness from the number of activated hair cells (and louder sounds activate greater numbers of hair cells).