Chapter 11: Hearing Flashcards
functions of hearing
- Hearing serves an important signalling function
- It adds richness to our lives through music
- It facilitates communication through speech
sound
describes both a physical stimulus and a perceptual response
physical definition of sound
sound is pressure changes in the air or other medium
the physical definition of sound is a type of ___
sensation
Perceptual definition
sound is the experience we have when we hear
the perceptual definition of sound is a type of ___
perception
sound wave
the pattern of air pressure changes
speed of sound through air
340 m/s
speed of sound through water
1500 m/s
compression/condensation
an increase in the pressure of air molecules
rarefaction
a decrease in the pressure of air molecules
location of air molecules during pressure changes
Although air pressure changes move outward from the source, the air molecules at each location move back and forth and they stay in about the same place
pure tone
when changes in air pressure occur in a pattern described by a sine wave
frequency
the number of cycles per second that the pressure changes repeat
how is frequency measured
hertz
what does hertz represent
the number of cycles per second; 1 Hz represents 1 cycle/second
what is the range of frequencies that humans can detect?
20-20,000 Hz
what perceptual dimension is frequency associated with?
pitch
amplitude
the size of the pressure change
how is amplitude measured?
Decibels (dB)
decibels
a perceptual unit that converts a large range of sound pressures into a more manageable scale
what perceptual dimension is amplitude associated with?
loudness
how are decibels calculated?
dB= 20 x log 10 (p/po)
what does p represent in the decibel equation
the pressure of the sound wave we are considering
what does po represent in the decibel equation?
the reference pressure, usually set at 20 micro pascals (the pressure near the hearing threshold for a 1,000 Hz tone)
Sound pressure level (SPL)
indicates that decibels were determined using the standard pressure of 20 micro pascals
sound level
the sound pressure of a sound stimulus in decibels
are most sounds in the environment sine waves?
no, most sounds in the environment are made up of complex tones, which have more complex patterns than a sine-wave
are complex tones periodic waveforms?
yes
complex tones
made up of pure tone sine-wave components that are added together
periodic waveform
a pattern of repeating pressure changes
fundamental frequency
the first harmonic of a complex tone; usually the lowest frequency in the frequency spectrum of a complex tone.
harmonics
pure-tone components of a complex tone that have frequencies that are multiples of the fundamental frequency
first harmonic
usually the lowest frequency in the frequency spectrum of a complex tone.
fundamental
a pure tone with a frequency equal to the fundamental frequency of a complex tone
higher harmonics
pure tones with frequencies that are whole number multiples of the fundamental frequency
frequency spectra
a plot that indicates the amplitude of the various harmonics that make up a complex tone.
repetition rate
the spacing between harmonics
what happens to the repetition rate if a harmonic is removed?
The repetition rate remains the same even if the fundamental or higher harmonics are removed because the spacing between harmonics remains intact
loudness
a perceptual quality most related to the level or amplitude of an auditory stimulus
audibility curve
a curve that indicates the sound pressure level (SPL) at the threshold for frequencies across the audible spectrum
auditory response area
shows the range of response for human audition. falls between the audibility curve and the threshold for feeling
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
pitch
the property of auditory sensation in terms of which sounds may be ordered on a musical scale extending from high to low
what is pitch associated with?
the repetition rate of the sound waveform of the fundamental frequency
tone height
the increasing pitch that accompanies increases in a tone’s fundamental frequency
tone chroma
the perceptual similarity of notes separated by one or more octaves
octave
tones that have frequencies that are binary multiples of each other
effect of the missing fundamental
the fact that pitch remains the same even when the fundamental or other harmonics are removed
timbre
the quality that distinguishes two tones that sound different even though they have the same loudness, pitch and duration. Differences in timbre are illustrated by the sounds made by different musical instruments,
how are different timbres created?
- Differences in the harmonics of different instruments
- The time course of a tone’s attack and decay
attack
the buildup of sound at the beginning of the tone
decay
the decrease in sound at the end of the tone
periodic sounds
a sound stimulus in which the pattern of pressure changes repeats
aperiodic sounds
a sound stimulus in which the pattern of pressure changes and does not repeat
how does the auditory system transduce pressure changes into electrical signals?
- The auditory system delivers the sound stimulus to the receptors
- It transduces this stimulus from pressure changes into electrical signals
- It processes the electrical signals so they can indicate the qualities of the sound source
outer ear
composed of the pinna and the auditory canal
pinnae
the part of the ear that is visible on the outside of the head. it helps with sound location
auditory canal
tube-like 3 cm long structure that protects the delicate structures of the middle ear
Tympanic membrane/eardrum
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
resonance
A mechanism that enhances the intensity of certain frequencies because of the reflection of sound waves in a closed tube
what frequencies does resonance in the auditory canal enhance?
1,000-5,000 Hz
resonant frequency
The frequency that is most strongly enhanced by resonance
how is the resonant frequency of a closed tube determined?
by the length of the tube
middle ear
the small air-filled space between the auditory canal and the cochlea that contains the ossicles
ossicles
three small bones in the middle ear that transmit vibrations from the outer ear to the inner ear
malleus
the first of the ossicles in the middle ear. Receives vibrations from the tympanic membrane and transmits them to the incus.
incus
the second of the three ossicles of the middle ear. It transmits vibrations from the malleus to the stapes
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
oval window
a small, membrane-covered hole in the cochlea that receives vibrations from the stapes
importance of the middle ear
The mismatch between the low density of air (outer ear) and the high density of the liquid (inner ear) means that without the middle ear, 1% of the information would be transmitted.
how do the ossicles solve the differences in density between the outer and inner ear?
- Concentrating the vibration of the large tympanic membrane onto the stapes, increasing the pressure
- Being hinged to create a lever action
middle-ear muscles
tiny skeletal muscles that are attached to the ossicles and contract to dampen their vibration, reducing the transmission of low-frequency sounds
inner ear
the innermost division of the ear, containing the cochlea and the receptors for hearing
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.
Scala vestibuli
the upper half of the cochlea
Scala tympani
the lower half of the cochlea
cochlear partition
A partition in the cochlea, extending almost its full length, that separates the scala tympani and the scala vestibuli. The organ of the Corti, which contains the hair cells, is part of the cochlear partition.
organ of corti
The major structure of the cochlear partition, containing the basilar membrane, the tectorial membrane, and the receptors for hearing
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.
what do vibrations to the cochlear partition cause?
the tectorial membrane to bend the hair cells by rubbing against them
stereocilia
Thin processes that protrude from the tops of the hair cells in the cochlea that bend in response to pressure changes
hair cells
Neurons in the cochlea that contain small hairs, or cilia, that are displaced by the vibration of the basilar membrane and fluids inside the inner ear.
two types of hair cells
inner & outer
inner hair cells
Auditory receptor cells in the inner ear that are primarily responsible for auditory transduction and the perception of pitch.
outer hair cells
Auditory receptor cells in the inner ear that amplify the response of inner hair cells by amplifying the vibration of the basilar membrane.
how many inner hair cells are in the human ear?
3,500 inner hair cells
how many outer hair cells are in the human ear?
12,000 outer hair cells
What do vibrations of the basilar membrane cause?
- Set the organ of Corti into an up-and-down vibration
- Cause the tectorial membrane to move back and forth
- These two motions lead to the bending of stereocilia
steps of auditory transduction
- The stereocilia of the hair cells bend in one direction
- This causes tip links to stretch
- Tiny ion channels are opened in the membrane of the stereocilia
- Positively charged potassium ions flood into the cell and an electrical signal results
- When the stereocilia bend in the other direction, the tip links slacken and ion channels close
what does the bending of stereocilia cause?
alternating bursts of electrical signals and no electrical signals
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
what happens to stereocilia when pressure increases?
stereocilia bend to the right, activating hair cells
what happens to stereocilia when pressure decreases?
stereocilia bend to the left, resulting in no electrical signal
phase locking
the property of firing at the same place in the sound stimulus
does the nerve always fire after pressure changes?
For high-frequency tones, the nerve might not always fire after the pressure changes due to the refractory period
Georg von Bekesy, 1960 experiment
determined how the basilar membrane vibrates by boring a hole in the cochleas taken from animal and human cadavers and observing vibrations when presented with different frequencies
Georg von Bekesy, 1960 findings
Found that the place that vibrates the most depends on the frequency of the tone
travelling wave
in the auditory system, vibrations of the basilar membrane in which the pearl of the vibration travels from the base of the membrane to its apex
apex
the end of the cochlea farthest from the middle ear. responds best to low frequencies
base
the end of the cochlea nearest to the middle ear. responds best to high frequencies
tonotopic map
an ordered map of frequencies created by the responding of neurons within structures in the auditory system
where is the tonotopic map?
There is a tonotopic map in the cochlea, with neurons at the apex responding best to low frequencies and neurons at the base responding to high frequencies. it is also present in the primary auditory cortex (A1)
evidence for the cochlea as a filter
- The neurons respond best to one frequency
- Each frequency is associated with nerve fibres located at a specific place on the basilar membrane
frequency tuning curve
a measurement of the response of auditory nerve fibres to a frequency
Measuring a person’s frequency tuning curve
- Present pure tones of different frequencies
- Measure the sound level necessary to cause the neuron to increase its firing above its baseline rate in the absence of sounds
- Plot the threshold for each frequency
characteristic frequency
the frequency to which the neuron is the most sensitive
cochlear amplifier
Expansion and contraction of the outer hair cells in response to sound sharpen the movement of the basilar membrane to specific frequencies. This amplifying effect plays an important role in determining the frequency selectivity of auditory nerve fibres.
the main purpose of outer hair cells
to influence the way the basilar membranes vibrate, which they accomplish by changing the length
what happens when there is ion flow in outer hair cells?
causes mechanical changes inside the cell that lead the cell to expand and contract. This increases the motion of the basilar membrane
place theory
the proposal that the frequency of a sound is indicated by a place along the organ of Corti at which nerve firing is the highest
what provided inspiration for place theory?
Bekesy’s travelling wave theory
main argument against place theory
The effect of the missing fundamental
modified place theory
considers how the basilar membrane vibrates to complex tones
resolved harmonics
harmonics in a complex tone that create separated peaks in basilar membrane vibration, and so can be distinguished from one another
resolved harmonics relative to complex tones
resolved harmonics are usually lower harmonics of a complex tone
what is the result of a series of resolved harmonics?
a strong perception of pitch
unresolved harmonics
harmonics of a complex tone that can’t be distinguished from one another because they are not indicated by separate peaks in the basilar membrane vibration
The higher harmonics of a tone are ___
most likely to be unresolved
what is the result of a series of unresolved harmonics?
weak perception of pitch
noise
a sound stimulus that contains many random frequencies
amplitude-modulated noise
a noise sound stimulus that is amplitude modulated
amplitude modulation
adjusting the level of a sound stimulus so it fluctuates up and down
Burns & Viemeister, 1976 pitch perception experiment
found that noise stimulus resulted in a perception of pitch, which they could change by varying the rate of the up-and-down changes in level. This demonstrates that pitch can’t be perceived even in the absence of place information
when do pitch perception and phase locking occur?
only occur for frequencies up to 5,000 Hz
temporal coding
the connection between the frequency of a sound stimulus and the timing of the auditory nerve fibre firing
what do most researchers believe is the major mechanism of pitch perception?
temporal coding
Oxenham et al., 2011 phase locking and pitch perception experiment
showed that if a large number of high-frequency harmonics are presented, participants perceive pitch. This suggests that phase locking might occur past 5,000 Hz
steps from the ear to the brain
- Signals generated in the hair cells are transmitted in the nerve fibres of the auditory nerve
- The auditory nerve carries the signals along the auditory pathway, eventually reaching the auditory cortex
- Auditory fibres synapse into subcortical structures
- The subcortical structure begins with the cochlear nucleus, then continues to the superior olivary nucleus, the inferior colliculus, and the medial geniculate nucleus (SONIC MG)
- From the MGN, information continues to the primary auditory cortex
subcortical structures
structures below the cerebral cortex
cochlear nucleus
The nucleus where nerve fibres from the cochlea first synapse
Superior olivary nucleus
A nucleus along the auditory pathway from the cochlea to the auditory cortex. The superior olivary nucleus receives inputs from the cochlear nucleus.
Inferior colliculus
A nucleus in the hearing system along the pathway from the cochlea to the auditory cortex. The inferior colliculus receives inputs from the superior olivary nucleus
Medial geniculate nucleus
An auditory nucleus in the thalamus that is part of the pathway from the cochlea to the auditory cortex. The medial geniculate nucleus receives inputs from the in- ferior colliculus and transmits signals to the auditory cortex
Bendor & Wang, 2005 pitch neurons experiment
found neurons in the marmoset that responded similarly to complex tones with the same fundamental frequency but with a different harmonic spectrum.
pitch neurons
A neuron that responds 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
Norman-Haignere et al., 2013 pitch and the brain experiment
located areas in the primary auditory cortex and some nearby areas that responded more to a pitch-evoking stimulus (resolved harmonics).
where are the neurons that are most responsive to pitch?
the anterior auditory cortex
how many people suffer from hearing loss
~17% of the U.S. adult population
why does hearing loss occur?
- Noise in the environment
- Damage to the outer hair cells
- Damage to auditory fibres
Presbycusis
hearing loss caused by hair cell damage resulting from the cumulative effects over time of noise exposure, the ingestion of drugs that damage the hair cells, and age-related degeneration
who is MORE affected by Presbycusis
Affects males more severely than females
who is LESS likely to experience large decreases in high-frequency hearing?
People in pre-industrial cultures, those who have not been exposed to the noises that accompanied industrialization, or to drugs that could damage the ear
noise-induced hearing loss
occurs when loud noise causes degeneration of the hair cells
damage to what auditory structure is associated with noise-induced hearing loss?
organ of the Corti
leisure noise
loud noises involved with recreational activities
hidden hearing loss
difficulties hearing in noisy environments despite otherwise normal hearing
audiogram
a plot of hearing loss vs. frequency
how is normal hearing represented on an audiogram?
Normal hearing is represented by a horizontal function at 0 dB
downside of audiograms
it doesn’t account for complex sounds
Kujawa & Liberman, 2009 hearing loss in mice experiment
exposed mice to a 100-dB SPL noise for 2 hours and then measured hair cell and auditory nerve function. Found that one day after the noise exposure, hair cell function decreased, but after 8 weeks, it had returned almost to normal.
condensation and rarefaction create ____
alternating high and low-pressure regions that travel through the air
function of the decibel scale
relates the amplitude of the stimulus with the psychological experience of loudness
what types of tones are periodic?
Both pure and some complex tones
periodic complex tones
consist of several pure tones called harmonics
additive synthesis
multiples of the fundamental frequency
what frequencies are humans MOST sensitive to?
2,000-4,000 Hz
how is the equal loudness curve determined?
using a standard 1,000 Hz tone
equal loudness curves show that:
- At almost equal loudness at 80 dB
- Softer at 40 dB for high and low frequencies than the rest of tones in this range
the resonant frequency of the auditory canal
1,000- 5,000 Hz
what are the three ossicles?
malleus, incus, and stapes
function of the ossicles
- Outer and inner ears are filled with air
- Inner ear is filled with fluid that is much denser than air
- Pressure changes in the air transmit poorly into the denser medium
- Ossicles act to amplify the vibration for better transmission to the fluid
- Middle ear muscles dampen the ossicles’ vibrations to protect the inner ear from potentially damaging stimuli
neural frequency tuning curves
pure tones are used to determine the threshold for specific frequencies measured at single neurons. Plotting thresholds for frequencies results in tuning curves
pure tones
created by a sine wave
pitch vs. frequency
Perception of pitch is related to frequency
additional harmonics
multiples of the fundamental frequency
what two decibel levels does the equal loudness curve use?
40 and 80
periodicity of pitch
a sound with the same perceived pitch, but with a different timbre
steps of phase locking
- Nerve fibres in bursts
- Firing bursts happen at or near the peak of the sine-wave stimulus
- Thus they are locked in place with the wave
- Groups of fibres fire with periods of silent intervals creating a pattern of firing
which theory of hearing is preferred?
- Up to 5,000 Hz (low frequencies)= phase locking/ temporal coding
- Above 5,000 Hz (high frequencies)= place theory
what happens when outer hair cells are removed?
the threshold for detection increases
what does SONIC MG mean & represent?
- the structures that receive auditory input
- SON= superior olivary nucleus
- IC= inferior colliculus
- MG= medial geniculate nucleus
how do neurons in A1 fire?
they preferentially fire to some frequencies
cochlear implants
Electrodes are inserted into the cochlea to electrically stimulate auditory nerve fibres
cochlear implants are made up of:
- A microphone that is worn behind the ear
- A sound processor
- A transmitter mounted on the mastoid bone
- A receiver surgically mounted on the mastoid bone
