Chapter 4: The physics and biology of audition
Key Terms in this Chapter
- amplitude
The maximum height of a wave, measured from its mean value to its maximum value.
<< back to topic- auditory association cortex
Two concentric bands of cortex encircling primary auditory cortex, containing cells responsive to auditory stimuli.
<< back to topic- azimuth
Direction in the horizontal plane, relative to straight ahead.
<< back to topic- basilar membrane
The flexible structure on the cochlear partition that houses mechanoreceptors; it forms part of the organ of Corti.
<< back to topic- cochlea
The spiral-shaped structure in the inner ear containing mechanoreceptors for hearing.
<< back to topic- cochlear nuclei
The mass of nerve cells in the brainstem where auditory nerve fibres terminate.
<< back to topic- cochlear partition
The flexible structure separating the scala vestibuli and scala tympani.
<< back to topic- complex wave
A wave that can be decomposed into a collection of simple, sinusoidal waves.
<< back to topic- decibels (dB)
A measure of the difference between two quantities, based on the logarithm of their ratio (so equal ratios between the quantities correspond to equal dB differences).
<< back to topic- dynamic range
In auditory nerve fibres, it is the difference between the minimum SPL to which a fibre responds, and the SPL at the fibre's maximum firing rate.
<< back to topic- ear canal
The S-shaped tube leading from the meatus to the tympanic membrane; it is approximately 0.6 cm wide and 2.5 cm long.
<< back to topic- Fourier analysis
The mathematical procedure by which a complex signal is decomposed into its magnitude spectrum and phase spectrum.
<< back to topic- Fourier spectrum
A representation of the magnitude of individual frequency components present in a signal such as a sound wave; it is also known as the magnitude spectrum.
<< back to topic- frequency
The number of cycles (periods) of a wave per unit of time or distance.
<< back to topic- frequency filter
Any process that modifies the frequency content of signals passing through it.
<< back to topic- 'frequency-to-place' conversion
The fact that the place of maximum displacement on the basilar membrane depends on the frequency of sound vibration.
<< back to topic- fundamental frequency
The lowest sinusoidal frequency in a complex wave.
<< back to topic- Harmonic frequency
A sinusoidal component of a complex wave, having a frequency that is an integer multiple of the fundamental frequency.
<< back to topic- impedance
The degree of resistance offered by a medium to an oscillating signal.
<< back to topic- impedance matching
The boost in pressure at the oval window provided by the mechanical properties of the middle ear, it matches up the differing acoustic impedances of air and inner-ear fluid.
<< back to topic- inner ear
The fluid-filled organ lying in the temporal bone, containing mechanoreceptors for hearing and balance.
<< back to topic- inner hair cells
The mechanoreceptors on the basilar membrane that provide afferent signals to the auditory system when the membrane is displaced.
<< back to topic- inter-aural level difference (ILD)
A difference in the intensity of an auditory stimulus arriving at the one ear relative to the other.
<< back to topic- inter-aural time difference (ITD)
A difference in the time of arrival of an auditory stimulus at one ear relative to the other.
<< back to topic- Linear filters
A frequency filter that modifies the amplitude of input frequency components, but does not introduce components that were not present in the input.
<< back to topic- meatus
The opening into the ear canal.
<< back to topic- medial geniculate nucleus
The obligatory relay station for all ascending projections in the auditory system, en route to the cortex.
<< back to topic- middle ear
The air-filled cavity containing the bones and associated supporting structures that transfer sound energy from the outer ear to the inner ear.
<< back to topic- non-linear filter
A frequency filter that distorts signals by adding new frequencies or by failing to respond at very low or high amplitudes.
<< back to topic- organ of Corti
The complex structure that forms part of the cochlear partition; it contains mechanoreceptors sandwiched between two flexible membranes.
<< back to topic- oto-acoustic emissions
A sound emitted from the ear, either spontaneously or following auditory stimulation.
<< back to topic- outer ear
The outermost components of the auditory system: the pinna, meatus, and ear canal.
<< back to topic- outer hair cells
Motile hair cells spanning the gap between the basilar membrane and tectorial membrane; they control the mechanical coupling between the two membranes.
<< back to topic- oval window
The point of entry for sound energy into the inner ear; it is a small membrane-covered opening in the cochlea.
<< back to topic- phase
A measure of the timing or position of a wave relative to a fixed point of reference, or to another wave.
<< back to topic- Phase locking
The firing of hair cells in synchrony with the variation of pressure in a sound wave.
<< back to topic- phase spectrum
A representation of the relative phases of individual frequency components present in a signal.
<< back to topic- pinna
The external ear visible on each side of the head; its shell-like inner part (concha) funnels sound into the meatus.
<< back to topic- Primary auditory cortex
The cortical destination of projections from the medial geniculate nucleus.
<< back to topic- scala tympani
The tube running along the cochlea that contains the round window at its base.
<< back to topic- scala vestibuli
The tube running along the cochlea that contains the oval window at its base.
<< back to topic- sine wave
A wave whose height varies smoothly so that it conforms to a mathematical sine function of time or distance (adjective: sinusoidal).
<< back to topic- Sound pressure level (SPL)
A decibel measure of sound pressure relative to a fixed reference pressure.
<< back to topic- spectrogram
A graphical representation of changes in the frequency content of a signal over time.
<< back to topic- superior olive
The complex of cells in the brainstem receiving projections from the cochlear nucleus; it contains binaural neurons that provide information about the location of sound sources.
<< back to topic- tectorial membrane
The flexible structure lying on top of the basilar membrane.
<< back to topic- tonotopic organisation
An organised arrangement of neurons, so that cells with similar frequency preferences lie close together in a neural structure.
<< back to topic- transfer function
A function that describes a linear filter's frequency response, in terms of the degree of attenuation at each frequency.
<< back to topic- travelling wave
The ripple of displacement that travels along the basilar membrane when sound vibrations are applied to the oval window.
<< back to topic- two-tone suppression
Suppression of an auditory nerve fibre's response to a tone during presentation of a second tone.
<< back to topic- tympanic membrane
The flexible cone-shaped membrane extending across the inner end of the ear canal; it transmits sound energy to the middle ear.
<< back to topic