| acoustic energy | The variations in air pressure produced by the vibration of an object.
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| acoustic reflex | Muscular contractions within the middle ear that damp sound vibrations by stiffening the eardrum and restricting the movements of the ossicles.
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| acoustics | The branch of physics concerned with sound.
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| adaptation | A reduction in the responsiveness of neurons, produced by prolonged stimulation.
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| amplitude | The property of sound waves that is related to the magnitude of the change in air pressure produced by a sound source. This property, sometimes referred to as intensity, is related to loudness. See intensity.
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| anvil (incus) | The middle member of the three ossicles within the middle ear; it relays sound vibrations from the hammer to the stirrup.
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| auditory canal | The hollow cavity leading from the pinna to the eardrum, which in humans is about 2.5 cm long and 7 mm in diameter.
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| auditory nerve | The bundle of nerve fibers innervating the cochlea and carrying information from the ear to higher stages of the auditory system. Also known as the eighth cranial nerve.
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| basilar membrane | The thin sheet of tissue separating the tympanic canal and the cochlear duct.
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| binaural | Listening with two ears. See monaural.
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| binaural cues | Sources of sound information for localizing a sound source by comparing the sounds received by the two ears.
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| cilia | A tiny tuft of thin hairs projecting out of each olfactory receptor cell and extending through the mucous layer into the nasal cavity; thought to be the site where odorous molecules trigger electrical changes in the olfactory receptor cell.
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| cochlea | A coiled, fluid-filled chamber in the inner ear containing the specialized organ for hearing, the basilar membrane.
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| cochlear emissions | Sounds that are generated entirely from within the cochlea.
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| cochlear nucleus | A structure receiving input from the auditory nerve; its cells exhibit a high degree of frequency tuning.
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| cortical deafness | Impaired hearing that results from damage to the auditory cortex.
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| decibel (dB) | A unit for expressing sound amplitude.
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| delay line | Key element in a theory designed to explain binaural cells' sensitivity to interaural time differences. The delay line retards the arrival of signals from one ear relative to those from the other ear.
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| eardrum (tympanic membrane) | The thin, oval membrane that covers the end of the auditory canal and separates the outer ear and the middle ear; it vibrates when sound waves strike it.
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| echoes | Reflected sound waves.
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| efferent fibers | In the auditory system, neural projections from the brain back to the cochlea.
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| Eustachian tube | The opening connecting the middle ear and the throat, which maintains air pressure within the middle ear at nearly the same value as the air pressure in the outside environment.
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| frequency tuning curve | A graph describing the sensitivity of an auditory neuron to tones of various frequencies.
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| hair cells | The ears' receptors. See inner hair cells, outer hair cells.
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| hammer (malleus) | The outermost of the three ossicles within the middle ear; one end of the hammer is attached to the eardrum, and the other end relays sound vibrations to the anvil.
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| hertz (Hz) | A unit for expressing the frequency with which the intensity of a sound or a light varies over time.
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| inner hair cells (IHCs) | The approximately 3.5 flask-shaped structures situated along the length of the basilar membrane of the human ear. See outer hair cells.
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| interaural intensity difference (IID) | The difference in the intensity of sound arriving at the two ears; one of the sources of information for sound localization. See interaural time difference.
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| interaural time difference (ITD) | The difference in the time of arrival of a sound wave at the two ears; one of the sources of information for sound localization. See interaural intensity difference.
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| medial geniculate nucleus | A structure in the thalamus that is part of the auditory system.
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| monaural | Listening with one ear. See binaural.
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| noise | A complex sound whose many constituent frequencies combine to produce a random waveform.
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| organ of Corti | The receptor organ for hearing, situated within the cochlear duct.
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| ossicles | A series of three tiny bones that transmit sound vibrations from the eardrum to the oval window. See anvil, hammer, stirrup.
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| outer hair cells (OHCs) | The approximately 12,000 cylindrical structures situated along the length of the basilar membrane of the human ear. See inner hair cells.
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| oval window | The small opening into the inner ear, which is covered by a thin membrane and which receives vibrations from the eardrum via the ossicles.
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| pinna | The part of the ear projecting from the side of the head; by influencing the frequency composition of sound waves entering the ear, this prominent structure plays a role in sound localization.
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| place theory | The idea that different portions of the basilar membrane vibrate in response to different sound frequencies. See frequency theory.
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| pure tones | Sinusoidal variations in sound pressure, such as those produced by striking a tuning fork.
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| resonant frequency | The frequency at which a given object vibrates when set into motion.
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| round window | The thin membrane that covers a small opening into the middle ear; displacement of this membrane compensates for pressure variations within the cochlea.
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| sound pressure level (SPL) | A reference level for sound intensity.
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| stirrup (stapes) | The innermost of the ossicles within the middle ear; attached to the oval window, it receives sound vibrations from the anvil and sets the oval window into vibration.
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| tectorial membrane | An awninglike layer of tissue arching over the hair cells within the inner ear.
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| threshold intensity | The minimum sound intensity necessary to elicit a neural response from an auditory neuron.
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| tinnitus | An annoying, persistent ringing in the ears.
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| tonotopic organization | The orderly layout of preferred frequencies over the length of the basilar membrane.
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| traveling wave | The movement of the basilar membrane in response to fluctuations in fluid pressure with the cochlea.
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2002 McGraw-Hill Higher Education