Chapter 11

Traveling wave

In the auditory system, vibration of the basilar membrane in which the peak of the vibration travels from the base of the membrane to its apex.

Frequency spectrum

A plot that indicates the amplitudes of the various harmonics that make up a complex tone. Each harmonic is indicated by a line that is positioned along the frequency axis, with the height of the line indicating the amplitude of the harmonic.

First harmonic

A pure tone with frequency equal to the fundamental frequency of a complex tone.

Fundamental

A pure tone with frequency equal to the fundamental frequency of a complex tone.

Oval window

A small, membrane-covered hole in the cochlea that receives vibrations from the stapes.

Periodic tone

A tone in which the waveform repeats.

Pure tone

A tone with pressure changes that can be described by a single sine wave.

Amplitude

In the case of a repeating sound wave, such as the sine wave of a pure tone, _____ represents the pressure difference between atmospheric pressure and the maximum pressure of the wave.

Sound level

The pressure of a sound stimulus, expressed in decibels.

Place theory of hearing

The proposal that the frequency of a sound is indicated by the place along the organ of Corti at which nerve firing is highest. Modern _____ is based on Békésy's traveling wave theory of hearing.

Auditory response area

The psychophysically measured area that defines the frequencies and sound pressure levels over which hearing functions. This area extends between the audibility curve and the curve for the threshold of feeling.

Loudness

The quality of sound that ranges from soft to loud. For a tone of a particular frequency, _____ usually increases with increasing decibels.

Pitch

The quality of sound, ranging from low to high, that is most closely associated with the frequency of a tone.

Tympanic membrane

A membrane at the end of the auditory canal that vibrates in response to vibrations of the air and transmits these vibrations to the ossicles in the middle ear.

Basilar membrane

A membrane that stretches the length of the cochlea and controls the vibration of the cochlear partition.

Tectorial membrane

A membrane that stretches the length of the cochlea and is located directly over the hair cells. Vibrations of the cochlear partition cause the _____ to bend the hair cells by rubbing against them.

Cochlear partition

A partition in the cochlea, extending almost its full length, that separates the scala tympani and the scala vestibuli. The organ of Corti, which contains the hair cells, is part of the _____.

Equal loudness curve

A curve that indicates the sound pressure levels that result in a perception of the same loudness at frequencies across the audible spectrum.

Sound pressure level (SPL)

A designation used to indicate that the reference pressure used for calculating a tone's decibel rating is set at 20 micropascals, near the threshold in the most sensitive frequency range for hearing.

Cochlear implant

A device in which electrodes are inserted into the cochlea to create hearing by electrically stimulating the auditory nerve fibers. This device is used to restore hearing in people who have lost their hearing because of damaged hair cells.

Presbycusis

A form of sensorineural hearing loss that occurs as a function of age and is usually associated with a decrease in the ability to hear high frequencies.

Noise-induced hearing loss

A form of sensorineural hearing loss that occurs when loud noises cause degeneration of the hair cells.

Audibility curve

A graph that indicates the sound pressure level (SPL) at threshold for frequencies across the audible spectrum.

Resonance

A mechanism that enhances the intensity of certain frequencies because of the reflection of sound waves in a closed tube. _____ in the auditory canal enhances frequencies between about 2,000 and 5,000 Hz.

Decibel (dB)

A unit that indicates the pressure of a sound stimulus relative to a reference pressure: _____=log (p/po) where p is the pressure of the tone and po is the reference pressure.

Tonotopic map

An ordered map of frequencies created by the responding of neurons within structures in the auditory system. There is a _____ of neurons along the length of the cochlea, with neurons at the apex responding best to low frequencies and neurons at the base responding best to high frequencies.

Eardrum

Another term for the tympanic membrane, the membrane located at the end of the auditory canal that vibrates in response to pressure changes. This vibration is transmitted to the bones of the middle ear.

Inner hair cell

Auditory receptor cell in the inner ear that is primarily responsible for auditory transduction and the perception of pitch.

Outer hair cell

Auditory receptor cells in the inner ear that amplify the response of inner hair cells by amplifying the vibration of the basilar membrane.

Frequency tuning curve

Curve relating frequency and the threshold intensity for activating an auditory neuron.

Cochlear amplifier

Expansion and contraction of the outer hair cells in response to sound sharpens the movement of the basilar membrane to specific frequencies. This amplifying effect plays an important role in determining the frequency selectivity of auditory nerve fibers.

Cilia

Fine hairs that protrude from the inner and outer hair cells of the auditory system. Bending the _____ of the inner hair cells leads to transduction.

Phase locking

Firing of auditory neurons in synchrony with the phase of an auditory stimulus.

Middle-ear muscles

Muscles attached to the ossicles in the middle ear. The smallest skeletal muscles in the body, they contract in response to very intense sounds and dampen the vibration of the ossicles.

Hair cell

Neuron in the cochlea that contains cilia, that are displaced by vibration of the basilar membrane and fluids inside the inner ear. There are two kinds of _____: inner and outer.

Pitch neurons

Neurons that respond to stimuli associated with a specific pitch. These neurons fire to the pitch of a complex tone even if the first harmonic or other harmonics of the tone are not present.

Leisure noise

Noise associated with leisure activities such as listening to music, hunting, and woodworking. Exposure to high levels of _____ for extended periods can cause hearing loss.

Sound wave

Pattern of pressure changes in a medium. Most of the sounds we hear are due to pressure changes in the air, although sound can be transmitted through water and solids as well.

Higher harmonics

Pure tones with frequencies that are whole-number (2, 3, 4, etc.) multiples of the fundamental frequency.

Harmonics

Pure-tone components of a complex tone that have frequencies that are multiples of the fundamental frequency.

Effect of the missing fundamental (periodicity pitch)

Removing the fundamental frequency and other lower harmonies from a musical tone does not change the tone's pitch.

Level

Short for sound pressure level or sound level. Indicates the decibels or sound pressure of a sound stimulus.

Tip links

Structures at the tops of the cilia of auditory hair cells, which stretch or slacken as the cilia move, causing ion channels to open or close.

Attack

The buildup of sound energy that occurs at the beginning of a tone.

Temporal coding

The connection between the frequency of a sound stimulus and the timing of the auditory nerve fiber firing.

Decay

The decrease in the sound signal that occurs at the end of a tone.

Apex of the cochlea

The end of the cochlea farthest from the middle ear.

Fundamental frequency

The first harmonic of a complex tone; usually the lowest frequency in the frequency spectrum of a complex tone. The tone's other components, called higher harmonics, have frequencies that are multiples of the _____.

Malleus

The first of the ossicles of the middle ear. Receives vibrations from the tympanic membrane and transmits these vibrations to the incus.

Characteristic frequency

The frequency at which a neuron in the auditory system has its lowest threshold.

Resonant frequency

The frequency that is most strongly enhanced by resonance. The _____ of a closed tube is determined by the length of the tube.

Tone height

The increase in pitch that occurs as frequency is increased.

Inner ear

The innermost division of the ear, containing the cochlea and the receptors for hearing.

Stapes

The last of the three ossicles in the middle ear. It receives vibrations from the incus and transmits these vibrations to the oval window of the inner ear.

Organ of Corti

The major structure of the cochlear partition, containing the basilar membrane, the tectorial membrane, and the receptors for hearing.

Frequency

The number of times per second that pressure changes of a sound stimulus repeat. _____ is measured in Hertz, where 1 Hertz is one cycle per second.

Base of the cochlea

The part of the cochlea nearest the middle ear.

Pinna

The part of the ear that is visible on the outside of the head.

Perceptual sound

The perceptual experience of hearing. The statement "I hear a sound" is using sound in that sense.

Tone chroma

The perceptual similarity of notes separated by one or more octaves.

Physical sound

The physical stimulus for hearing. The statement "The sound's level was 10 dB" is using sound in that sense.

Outer ear

The pinna and the auditory canal.

Timbre

The quality that distinguishes between two tones that sound different even though they have the same loudness, pitch, and duration. Differences in _____ are illustrated by the sounds made by different musical instruments.

Incus

The second of the three ossicles of the middle ear. It transmits vibrations from the malleus to the stapes.

Auditory canal

The section through which air vibrations travel from the environment to the tympanic membrane.

Middle ear

The small air-filled space between the auditory canal and the cochlea that contains the ossicles.

Cochlea

The snail-shaped, liquid-filled structure that contains the structures of the inner ear, the most important of which are the basilar membrane, the tectorial membrane, and the hair cells.

Hertz (Hz)

The unit for designating the frequency of a tone. One _____ equals one cycle per second.

Acoustic prism

The way the cochlea separates frequencies entering the ear to create activity at different places along the basilar membrane.

Ossicles

Three small bones in the middle ear that transmit vibrations from the outer to the inner ear.

Octave

Tones that have frequencies that are binary multiples of each other (2, 4, etc.). For example, an 800-Hz tone is one _____ above a 400-Hz tone.