Hearing and the auditory system Flashcards
What is sound?
Loudness and pitch conveyed by vibrations in the air to the ear and then to the auditory system.
What are the main parts of the auditory system?
The ear, the cochlea, the 8th cranial nerve, brainstem and midbrain, auditory cortex.
How does sound travel through the air?
In waves - the compression and expansion of air molecules (increase and decrease of pressure) produced by vibration.
What does the amplitude of the sine wave represent?
The amount of vibration.
What does the wavelength of the sine wave represent?
The frequency of vibration.
What does a Reubens’ tube show?
A standing wave of sound in fire! High pressure doesn’t allow gas to come out, low pressure allows more gas.
What is sound pressure, or P?
The root mean square of the deviation in pressure around the baseline atmospheric pressure (uPa).
What is sound intensity, or I?
The acoustical energy per unit time and unit area (W/m^2).
What does this mean: I=kP^2
Sound intensity is proportional to the square of the sound pressure.
What is the smallest detectable sound pressure/intensity?
20uPa or 10^-12 W/m^2.
What is the threshold for pain, and what factor is this of the smallest detectable sound?
10 W/m^2, 1 trillion.
What is the logarithmic scale used to represent sound pressure/intensity?
Decibel sound pressure level - dB SPL.
What is the threshold of hearing in decibels?
0dB.
How loud, in decibels, are leaves rustling?
About 20.
How loud, in decibels, is a library?
About 40.
How loud, in decibels, is an office or classroom?
About 70.
How loud, in decibels, is a heavy truck?
About 90.
How loud, in decibels, is a jackhammer?
105.
How loud, in decibels, is a plane taking off?
Over 130.
What is the pain threshold in decibels?
About 100dB.
What is the 10dB rule?
For every increase of 10dB, the sound level doubles.
What does uPa stand for?
Micro pascals.
What does Weber’s Law state?
The JND, deltaI, is proportional to the intensity I of the stimulus: deltaI/I = k
For sound intensity, what is the approximate value of k in Weber’s Law?
0.2
What does Weber’s Law imply for sound intensity?
We are sensitive to about a 20% change in intensity, approximately 1dB.
Why don’t we hear loud noises due to pressure changes when we walk?
The frequency when we walk is too low to hear. 2-3Hz.
How does the audibility threshold change with frequency?
As frequency increases, the threshold decreases, with a small peak around 800Hz.
What is the lowest frequency we can hear?
20Hz.
Can we detect sounds below 20Hz?
Yes, we feel them.
What is the highest frequency we can hear?
2000Hz.
What scale is used for frequency?
Level scale - log10 Frequency scale (octave) - log2.
What does the frequency range correspond to?
10 octaves.
Weber’s law applies to frequency discrimination. What does this mean?
JND deltaf is proportional to f.
According to Weber’s Law, what frequencies can we discriminate between?
- between 1000 and 1001 Hz
- Weber fraction (k) of 0.001
- a 0.1% change - a semitone is 6%.
How is pitch defined mathematically?
Asin(2pift+&)
Where A is sound pressure, f is frequency, and & is phase.
What drives our perception of pitch?
Frequency.
What are the three parts of the ear?
Outer, middle, inner.
What are the parts of the outer ear?
Concha, ear canal, pinna, and tympanic membrane (ear drum).
What are the parts of the middle ear?
Malleus, incus, tensor tympani muscle, stapes, tympanic membrane, stapedius muscle, round window, base of stapes in oval window,
What are the parts of the inner ear?
Semi-circular canals, oval window, vestibular nerve, auditory nerve (cochlear nerve?), cochlea, ?round window.
What can be seen in a cross section of the cochlea?
Tectorial membrane, vestibular canal, Reissner’s membrane, middle canal, inner hair cells, spiral ganglion, tympanic canal, basilar membrane, outer hair cells.
What do outer hair cells do?
They move with pressure changes, causing the release of ions, leading to the release of NTs and auditory nerve APs.
What is in the corti, the small centre section of the cochlea?
Tectorial membrane, stereocilia, afferent fibres, basilar membrane, inner and outer hair cells, tunnel of corti, and efferent fibres.
How does sound cause the movement of inner and outer hair cells?
Sound induces vibration of the tectorial membrane, which moves back and forth over the top of the hairs, alternating around 1000 times per second.
What is meant by frequency decomposition?
How we detect different frequency waves through the cochlea - different parts of it respond to different frequencies.
What type of frequency does the cochlea near the stapes (base) respond to?
High frequencies.
What part of the cochlea responds to low frequency sounds?
The apex.
What does Fourier analysis mean when applied to sound waves?
Through the combination of different waves, any sound can be made.
How does the brain amplify sounds of a certain frequency?
It causes the outer hair cells to amplify certain frequencies by pressing on the basilar membrane.
What is the difference between high and low spontaneous rate fibres?
High fibres respond more at low sound intensities and reach their maximum firing rate earlier than low fibres, which respond more to high sound intensities.
What is phase locking?
How firing rate responds to frequency - there is a delay between the highest pressure and the highest firing rate due to having to transmit through membrane, hairs, release ions and NTs, then causing APs.
What is frequency tuning?
The lowest intensity needed to cause an action potential in a particular neuron - low frequency at apex, high at stapes.
What is the idea of critical bands and auditory masking?
When pts are asked to detect a tone whilst hearing a masking noise, the more similar the frequencies are (whether they fall within a critical band) determines the signal threshold.
What brain structures are involved in the auditory system?
Auditory nerve, rostral medulla (dorsal, posteroventral and anteroventral cochlear nuclei), mid pons (superior olive), pons-midbrain junction (nucleus of lateral leminiscus), caudal midbrain (inferior colliculus), rostral midbrain (medial geniculate complex of the thalamus), and the cerebrum (primary auditory cortex).
Where does binaural processing occur?
In the mid pons - the superior olive. Input from both cochleas are combined.
What do LSO and MSO stand for?
Lateral and medial superior olive.
What are the two binaural cues?
Interaural time difference and interaural level difference.
What do binaural cues determine?
The location of the sound.
What does interaural time difference arise from?
The difference in distance and therefore time a sound needs to travel to reach each ear.
What is the maximum ITD in humans?
600 micro seconds.
What frequencies is ITD useful for, and why?
Below 1000Hz, because it requires phase locking.
Why does interaural level difference arise?
Because the head casts an acoustic shadow.
What is the maximum ILD in humans?
20dB.
What frequencies is ILD useful for?
Frequencies above 1000Hz.
What is an example of acoustic shadowing in everyday life?
Hearing the bass of music from a passing car, but not the higher frequencies as they’re shadowed by walls etc.
What frequency sounds do we have limited information on the location of and why?
1000Hz because of the boundaries of ITD and ILD.
What is reverberation?
How sounds reflect/echo off surfaces in rooms.
What is the precedence effect?
The fact that although sound reflections arrive at different times, the auditory system gives precedence to early arriving sounds, so we only hear the sound from one direction.
How do arctic foxes determine sound location without using their visual system?
They move their heads to better determine the location.
How well do barn owls determine sound location?
Very well, due to weirdly placed ears (by their eyes) aided by feathers, meaning that they encode ITD and ILD very well.
Where is speech processed?
The primary auditory cortex.
Name the main parts of the vocal tract used in producing phonemes.
Palate, tongue, epiglottis, vocal cords, larynx, trachea, oesophagus, and lungs.
Name the main parts of the vocal tract used in shaping sounds.
Nasal tract, hard palate, teeth, lower lip, jaw, tongue, epiglottis, pharynx, soft palate, oral tract, and alveolar ridge.
What three parts of the vocal tract are used for constrictions?
Teeth, lower lip, and tongue.
What does vowel output look like in terms of a graph of frequency by amplitude?
There are three formers - humps formed of amplification and attenuation.
How can the three vowel formers be moved (changing peak alignment), and what does this do?
By tongue position, forming different vowels.
What are the unvoiced plosive consonants?
P, t, and k.
What are the voiced plosive consonants?
B, d, and g.
What are the labial plosive consonants?
P and b.
What are the dental/alveolar plosive consonants?
T and d.
What are the velar (hard palate) plosive consonants?
K and g.
What are the nasal plosive consonants?
M and n.
What is the McGurk effect?
When a video of someone saying ‘gah’ with an audio track of ‘bah’ is presented to a participant, they interpret it as ‘dah’.
What are the applications of findings about hearing?
9 million hearing impaired individuals benefit from hearing aids.
Also affects room design and mp3 file compression (keeps sound with 90% size reduction).
