Chapter 9 & 10 Definitions
• amplitude: The magnitude of displacement (increase or decrease) of a sound pressure
wave or of a head movement (e.g., angular velocity, linear acceleration, tilt).
• intensity: The amount of sound energy falling on a unit area (such as a square
• frequency: For sound, the number of times per second that a pattern of pressure change
hertz (Hz): A unit of measure for frequency. One hertz equals one cycle per second.
• loudness: The psychological aspect of sound related to perceived intensity or magnitude.
• pitch: The psychological aspect of sound related mainly to the fundamental frequency.
• decibel (dB): A unit of measure for the physical intensity of sound. Decibels define the
difference between two sounds as the ratio between two sound pressures. Each
10:1 sound pressure ratio equals 20 dB, and a 100:1 ratio equals 40 dB.
• sine wave (or pure tone): The waveform for which variation as a function of time is a sine
• period: The time (or space) required for one cycle of a repeating waveform.
• phase: The relative position of two or more sine waves. For sounds, the phase is the
relative position in time.
• complex tone: A sound wave consisting of more than one sinusoidal component of
• Fourier analysis: A mathematical theorem by which any sound can be divided into a set
of sine waves. Combining these sine waves will reproduce the original sound.
• spectrum: A representation of the relative energy (intensity) present at each frequency.
• harmonic spectrum: The spectrum of a complex sound in which energy is at integer
multiples of the fundamental frequency.
fundamental frequency: The lowest-frequency component of a complex periodic sound.
• timbre: The psychological sensation by which a listener can judge that two sounds with
the same loudness and pitch are dissimilar. Timbre quality is conveyed by harmonics
and other high frequencies.
• pinna: The outer, funnel-like part of the ear.
• ear canal: The canal that conducts sound vibrations from the pinna to the tympanic
membrane and prevents damage to the tympanic membrane.
tympanic membrane: The eardrum; a thin sheet of skin at the end of the outer ear canal.
The tympanic membrane vibrates in response to sound.
• outer ear: The external sound-gathering portion of the ear, consisting of the pinna and the
• middle ear: An air-filled chamber containing the middle bones, or ossicles. The middle
ear conveys and amplifies vibration from the tympanic membrane to the oval
• ossicles: Three tiny bones of the middle ear: malleus, incus, and stapes.
• malleus: One of the ossicles. The malleus receives vibration from the tympanic
membrane and is attached to the incus.
• incus: The middle ossicle. The incus connects the malleus and the stapes. • stapes: One of the ossicles. Connected to the incus on one end, the stapes presses
against the oval window of the cochlea on the other end.
• oval window: The flexible opening to the cochlea through which the stapes transmits
vibration to the fluid inside.
• inner ear: A hollow cavity in the temporal bone of the skull, and the structures within this
cavity: the cochlea and vestibular canals.
• tensor tympani: The muscle attached to the malleus; tensing the tensor tympani
• stapedius: The muscle attached to the stapes; tensing the stapedius decreases vibration.
• acoustic reflex: a reflex that protects the ear from intense sounds, via contraction of the
stapedius and tensor tympani muscles
• cochlea: A spiral structure of the inner ear containing the organ of Corti.
• tympanic canal: One of three fluid-filled passages in the cochlea. The tympanic canal
extends from the round window at the base of the cochlea to the helicotrema at the
apex. Also called scala tympani.
• vestibular canal: One of three fluid-filled passages in the cochlea. The vestibular canal
extends from the oval window at the base of the cochlea to the helicotrema at the
apex. Also called scala vestibuli.
• middle canal: One of three fluid-filled passages in the cochlea. The middle canal is
sandwiched between the tympanic and vestibular canals and contains the cochlear
partition. Also called scala media.
• helicotrema: The opening that connects the tympanic and vestibular canals at the apex of
• Reissner’s membrane: A thin sheath of tissue separating the vestibular and middle
canals in the cochlea.
• basilar membrane: A plate of fibers that forms the base of the cochlear partition and
separates the middle and tympanic canals in the cochlea.
• cochlear partition: The combined basilar membrane, tectorial membrane, and organ of
Corti, which are together responsible for the transduction of sound waves into neural
• round window: A soft area of tissue at the base of the tympanic canal that releases
excess pressure remaining from extremely intense sounds.
• organ of Corti: A structure on the basilar membrane of the cochlea that is composed of
hair cells and dendrites of auditory nerve fibers.
• hair cells: Cells that support the stereocilia that transduce mechanical movement in the
cochlea and vestibular labyrinth into neural activity sent to the brain stem; some hair
cells also receive inputs from the brain.
• auditory nerve fibers: A collection of neurons that convey information from hair cells in
the cochlea to (afferent) and from (efferent) the brain stem. This collection also
includes neurons for the vestibular system.
• stereocilia: Hairlike extensions on the tips of hair cells in the cochlea that initiate the
release of neurotransmitters when they are flexed.
• tectorial membrane: A gelatinous structure, attached on one end, that extends into the
middle canal of the ear, floating above inner hair cells and touching outer hair cells. • tip link: A tiny filament that stretches from the tip of a stereocilium to the side of its
• place code: Tuning of different parts of the cochlea to different frequencies, in which
information about the particular frequency of an incoming sound wave is coded by
the place along the cochlear partition that has the greatest mechanical
• afferent fiber: A neuron that carries sensory information to the central nervous system.
• efferent fiber: A neuron that carries information from the central nervous system to the
• threshold tuning curve: A map plotting the thresholds of a neuron or fiber in response to
sine waves with varying frequencies at the lowest intensity that will give rise to a
• characterisitc frequency (CF): The frequency to which a particu