Hearing Flashcards
1
Q
What are “sound”?
Is this the only thing that can elicit an auditory sensations
A
Small fluctuations in air pressure
No - any vibration transmitted to the ear can
2
Q
What can complex vibrations be resolved into
A
The sum of individual sinusoidal vibrations
3
Q
Describe a sine wave
A
An individual sinusoidal vibration
Characterised by 3 parameters: frequency, amplitude and phase
4
Q
Subjectively what do changes in amplitude and frequency of sine waves correspond to
A
Amplitude- loudness
Frequent- pitch
5
Q
How sensitive are we to changes of phase in sine waves
A
We are relatively insensitive to changes in the phase of a sound and thus there is no subjective correlate for phase
6
Q
What is the range of intensities that we can hear
A
> 10^12:1
7
Q
What is the unit of power used in auditory research
A
1/10 of a Bel (decibel)
Decibels are RATIOS!!!
8
Q
What is the reference value in human psychoacoustics
What is the importance of this
A
20μPa
The strength of the signal is indicated relative to this value
9
Q
What is 1Pa in N/m^2
A
1:1
10
Q
What is the frequency threshold for human hearing
A
3kHz
11
Q
What is dB SPL
A
Decibels sound pressure level
12
Q
What does 0 dB mean
A
The sound has the same pressure as reference (log1=0)
13
Q
How do you express a level of zero sound in dB
A
You can’t!!! Log0=-infinity
14
Q
Negative values of dB mean negative sound. True or false?
A
False
The specified sound is simply less than reference
15
Q
What does dB SPL=?
A
20log(Pressure/20μPa)
16
Q
What is the speed of sound
A
340m/s in air
17
Q
f=?
A
1/p
18
Q
What does λ=
A
(1/f)x c
where c = speed of sound (~ 340 metres/s in air)
19
Q
What is a band stop filter
A
Only passes frequencies outside a restricted bandwidth
20
Q
How can the auditory pathway be divided
A
Into peripheral (ear and auditory nerve) and central (nuclei and pathways from cochlear nucleus to auditory cortex)
21
Q
How is the ear divided
A
Outer - pinna and external auditory meatus
Middle - tympanic membrane, ossicles and middle ear cavity
Inner- cochlear (and vestibular apparatus)
22
Q
How does the ear canal act
A
As an open ended tube with resonant peaks that are predictable from knowing its height (2-3cm in man)
23
Q
Generally why is the pinna useful
A
Can assist in sound localisation by modifying spectra of sounds in a space dependant manner
24
Q
Where is the azimuthal location of 90 degrees
A
Directly in line with left pinna
25
What is HRTF
Where do direction dependant notches and peaks appear
Head related transfer function
The pressure transformation from free field to the tympanic membrane
Above 5kHz
26
What does the first spectral notch of the HRTF provide
A cue for sound localisation, particularly elevation (vertical plane)
27
What happens when we fit a mold to the external ear
What happens if it is left in for several weeks
Why
What happens after its removal
What does this suggest
Disrupts the ability to make judgements about elevation
Errors in localisation disappear after time - they had learnt to associate new spectral cues with direction in space
Could localise just as well immediately after
Multiple representations of auditory space can co-exist
28
Given that it took several weeks for a new representation to be formed after insertion of a mould into the external ear how would this presentation be formed
What is this similar to
By neural growth of novel connections
Being bilingual - first and second languages are processed un different regions of the cortex
29
What are the functions of the middle ear (3)
Impedance matching between air and cochlear folds
Protection from loud sounds (including own vocalisations)
Anti masking or high frequency sounds by low frequency sounds (particularly at high sound levels)
30
What is the purpose of the middle ear muscles
To dampen the vibrations of the ossicles thereby reducing the acoustic signal that reaches the ears
31
When do the middle ear muscles contract
100ms AFTER exposure to a loud sound and BEFORE a person vocalises
32
Do frogs have middle ear muscles
No as they do not vocalise
33
True or false
Middle ear muscles attenuate high frequencies more than low
Faults they attenuate low frequencies more than high
34
Where do the tensor tympani and stapedius attach
TT- neck of malleus
Stapedius- neck of stapes
35
Which muscles in humans are active when exposed to loud sounds
Only stapedius
36
What is the threshold for the middle ear muscle reflex to be activated
Is this bilateral or unilateral
Sounds 80 dB above a persons hearing threshold
Reflex is seen in both ears even if one is stimulated alone
37
How does the sensory side of the acoustic reflex circuit travel
Via CN VIII to ipsilateral ventral cochlear nucleus (VCN)
Output from the ventral cochlear nucleus then goes to the superior olivary complex on both sides of the brainstem which in turn projects to the facial nerve nuclei on their respective sides
38
Describe the a
| efferent arm of the acoustic reflex circuit
Goes from the facial nuclei to enable contraction of the stapedius muscles in both ears
39
What is the main purpose of stapedius in birds
To reduce intensity of the sound produced when the bird cries/sings
40
What happens in a middle ear infection
Middle ear cavity filled with fluid and a low frequency hearing loss of 30 dB or greater may develop
41
In a middle ear infection Middle ear cavity filled with fluid and a low frequency hearing loss of 30 dB or greater may develop. What kind of hearing loss is this?
What is the other kind of hearing loss
Conductive loss
Sensorineural hearing loss (If the cochlear auditory pathway is damaged)
42
Name a test to distinguish between conductive and sensorineural hearing loss
Rinne test
The examiner place is a vibrating tuning fork alternatively on the mastoid process and at the entrance of the external auditory meatus
If the deafness is conductive bone conduction is unimpaired while the response to sound conducted by the external auditory meatus is reduced
If deafness is sensorineural detached shows a greater sensitivity to air-conduction at the external auditory meatus in comparison with bone conduction
43
What is the main structure of interest in the inner ear
Cochlea
44
What is the principal function of the cochlea
To decompose the acoustic signal into its component frequencies
45
How can the cochlea be considered functionally
Although it is coiled like a snail shell it can be considered as a straight tube compartmentalised longitudinally
46
Where do the scala vestiubli and scala tympani meet
At the helicotrema
47
Where is the scala media
A longitudinal partition between the scala vestbuli and scala tympani
48
What happens when stapes vibrates at the oval window
How is the cochlear partition (basilar membrane)designed
The incompressible fluids in the cochlea vibrate, causing the round window to bulge outwards
The cochlea partition is narrower and stiff it near its base than it’s apex and therefore vibrates Maximally for high frequency sound is near the base and maximally the low-frequency sounds near its apex
49
How are frequencies mapped out along the basilar membrane
Tonotopically along its length with equal increments in distance corresponding to equal increments in logarithmic frequency (mapping is non linear)
50
Describe the two types of hair cell in mammalian cochlea
1 row of inner hair cells (IHCs)
3 rows of outer hair cells (OHCs)
51
How many inner and outer hair cells are there
Inner ~ 3000
| Outer ~ 11000
52
What are type 1 auditory fibres
The majority of auditory nerve fibres (90%) which synapse with the inner hair cells
53
What are type II fibres (hearing)
Unmyelinated cells that contact the outer hair cells and make up 10% of auditory nerve fibres
54
What are the two types of olivocochlear neuron
Medial olivocochlear neuron which projects to the outer hair cells
Lateral olivocochlear neuron which project to the primary afferents beneath the inner hair cells
55
Give 3 facts about basilar membrane vibration
Each point undergoes a sinusoidal vibration at the driving frequency
Max amplitude of vibration corresponds to the characteristic place on the cochlea’s frequency map
The pattern of vibration is not dependant on which end of the cochlea is stimulated
56
Does hearing change in death
Yes
Cadavers do not hear as well as humans
57
What are the agents if the mechanical feedback system in cochlear function
Outer hair cells
58
Name three lines of evidence to support the idea of outer hair cell active feedback
Many aspects of cochlear function or physiologically vulnerable
The ear can emit sound - otoacoustic emissions
Interruption of 0HC alters the IHT response
59
How do the outer hair cells change shape
Depolarisation causes length to decrease
Hyperpolarisation causes length increase
This allows accentuation of the sound vibration
60
Give the overall function of the inner and outer hair cells
Inner: Act to transducer the mechanical events in the cochlea to electrical events in the auditory nerve fibres
Alter: actively assist the mechanics of the cochlear and are responsible for sensitivity, sharpness of tuning and oto-acoustic emissions
61
In the cochlear physiological displacement of the stereocilia is caused by what
A relative movement between the reticular laminar and the tectorial membrane (OHCs) or by the flow of endolymph over the cilia (IHCs)
62
Where does transduction in hair cells take place
At the tips of the stereocilia
63
What happens if the stereocilia are stretch towards the tallest stereocilia?
What else will have this effect
The probability of the mechanically gated channels opening increases
If stretched towards kinocilium in the vestibular apparatus
64
What happens if the stereocilia stretched away from the tallest stereocilia?
Where did this idea come from
The probability of the mechanically gated ion channels closing increases
The observation that the largest current changes occur near the tips of the stereocilia rather than at the base. The mechanical casing is thought to be controlled by tip links which connects the stereocilia
65
How do the tip links of the stereocilia work
Stretching of the tip links, cause by displacing the bundle towards the largest stereocilia, is excitatory
Movement in the opposite direction is inhibitory
66
What carries the transducer current in stereocilia?
What is the driving force
K+ ions
Entirely electrical
67
What is the predominant cation in the endolymph
K+
68
What is the resting membrane potential of the stereocilia cells
What is this couples to
Why is this arrangement important
-50mV
This is coupled with the large Endocochlear potential of +100mV
This gives a total gradient of 150mV
It means that few metabolic demands are placed on the hair cell to maintain its intra cellular composition – rather, active transport is needed to maintain the composition of the endolymph
69
How is the composition of the endolymphatic fluid controlled
By the stria vascularis
70
What is presbycusis?
The increasing of our hearing thresholds with age
71
In men, are thresholds for higher frequencies poorer or better than for lower frequencies?
What about for women?
Thresholds for both men and
women are poorer in the high frequencies than
the lower frequencies.
72
Hearing thresholds above which frequency are affected by ageing?
Why is this relevant to us ?
8Hz
this is not usually measured clinically
73
What is the greatest factor affecting presbycusis?
the loss of the endocochlear potential arising from lateral wall degeneration with age
74
How can we test the hypothesis that presbycusis is mainly due to loss of the
endocochlear potential arising from lateral wall
degeneration with age
s, it
is possible to selectively lower the EP in just one
ear by application of furosemide to the round
window. The resulting threshold loss seen with presbycusis
reduction in the EP mimics that seen
75
Describe the hearing loss of presbycusis
a relatively flat loss at low
frequencies and a sloping loss at high
frequencies.
76
What are OAEs?
otoacoustic emissions -sounds that
may be measured in the external auditory
meatus
77
What evokes OAEs
sound
may occur spontaneously - evidence of the active process in hearing
78
How many people have spontaneous OAEs
about 50% of
| normal hearing humans have these
79
What are Distortion product evoked otoacoustic
| emissions (DPOAEs)
generated with the
presentation of two tones (aka the primaries, f1
and f2) and the largest of these emissions occurs
at the frequency 2f1 – f2
80
What are OAEs like in patients with sensorineural hearing loss
Patients with a
| significant sensorineural hearing loss lack OAEs.
81
When is measurement of OAEs useful
in neonates where it is difficult to
| establish the absence of hearing.
82
What do IHCs release?
What does this act on
Glutamate from ribbon synapses
AMPAr on primary afferents (auditory nerve fibres)
83
Where does adaptation to a tone burst occur in the hearing pathway
at the hair cell-afferent fibre synapse
84
How can the output of the auditory nerve be considered
as a set of parallel, overlapping, bandpass
| filters
85
How do filters change for different frequencies in the nervous system?
narrower for higher frequencies
86
What is the measure used to characterise filters in
a) engineering
b) to test hearing
a) Q3 dB
| b) Q10 dB
87
What is the characteristic frequency of a filter?
the most sensitive point of the filter
88
True or false:
Tonotopicity is
preserved throughout the auditory pathway
true: from cochlear to cortex
| this is spatial frequency mapping
89
What is frequency resolution?
the ability to detect one
frequency component of a multi-frequency
complex stimulus, when all components are
presented simultaneously
90
When is frequency sensitivity determined?
at the level of the basilar membrane
91
Is there a relation between the psychophysical
| bandwidths and the neural bandwidths recorded
Yes - a strong positive correlation between equivalent bandwidth and CF on a double log graph
92
Do some auditory neurons have a preference for when they fire
yes
Low frequency auditory neurons discharge at
preferred phases of the stimulating signal.
93
Do phase locked neurons fire every cycle?
No but when they do fire they fire at the same point (phase) of the wave
94
What is the upper limit for phase locking for different animals
cat - 5000Hz
guinea pig - 3500Hz
Barn owl -8000Hz
95
Why might you think 1000Hz is the upper limit for phase locking
it is the upper limit of spike discharge as set by the refractory period
96
How can auditory nerve fibres be divided
groups based on their spontaneous discharge
| rate
97
What is spontaneous discharge rate defined as
defined as the discharge rate of an
auditory neuron in the absence of controlled
acoustic stimulation
98
Which auditory fibres have the highest spontaneous discharge rate?
those with the lowest threshold (the most sensitive)
99
What does the threshold of an auditory fibre determine?
its dynamic range
100
which auditory nerve fibres have a narrow dynamic range
Low threshold
fibres have the narrowest dynamic range, high
threshold fibres have the widest dynamic range.
101
What underlies our ability to perform discrimination of
small intensity differences over a wide range of sound
levels.
Of course, no
individual fibre can encode the entire range of sound
levels (> 100 dB) but combining the information from
the different fibre groups and an increase in the
number of active fibres at high sound levels allows discrimination
102
What does the olivocochlear efferent system supply?
How is it divided?
descending
fibres from the superior olive to the cochlea.
It is
divided into two - lateral and medial
103
Describe the lateral division of the olivocochlear system
has its cell bodies in or around
the lateral superior olive (depending on the
species
terminates on the dendrites
of the auditory nerve fibres
104
Describe the medial division of the olivocochlear system
has its cell bodies
medial to the lateral superior olive, in the periolivary region of the superior olive
directly contacts the outer hair cells.
105
What is the advantage of having both a medial and lateral division of the olivocochlear
The
brain is therefore able to influence the output of
both sets of receptor cells.
106
What is the role of the lateral olivocochlear system?
unknown
107
What are the 3 main hypotheses concerning the role of the medial olivocochlear system
protection from loud sounds
improving detection of sounds in noise (anti-masking)
controlling cochlear mechanics
108
Describe the hypothesised role of the medial olivocochlear system in protection from loud sounds
If loud tone exposure is accompanied by electrical stimulation of the
medial olivocochlear system, the following increase in
threshold is greatly reduced.
109
What is temporary threshold shift
an increase in threshold following exposure to a loud tone
110
when is a protection from an increase in threshold seen
When is this disrupted
when the
exposure to a loud stimulus in one ear is
accompanied by an acoustic stimulus in the
other ear.
if the
medial olivocochlear system is disrupted
111
How could you disrupt the olivocochlear system
. by
sectioning the olivocochlear bundle at the floor
of the fourth ventricle.
112
What does anti masking mean
Electrical stimulation of the medial olivocochlear
system can improve the detectability of signals
in noise.
113
What happens to detection and discrimination of vowel sounds when the olivocochlear bundle is cut?
detection
of vowel sounds is left intact when the
olivocochlear bundle is cut but
discrimination is impaired
114
What is masking?
the process by which the threshold of hearing for one sound is raised by the presence of another sound.
115
What is Auditory masking in the frequency domain known as
simultaneous
masking, frequency masking or spectral masking (i.e. a sound in one
frequency blocks the perception of another sound in another frequency, both occuring at the same time).
116
What is masking in the temporal domain known as
temporal masking or non-simultaneous masking (i.e. an earlier
sound blocks the perception of a later occuring sound).
117
How does antimasking work
Middle ear muscle reflex (MEMR) and Medial OlivoCochlear Reflex (MOCR) react to
sustained sounds and dampen them (the MEMR by stiffening the ossicle chain, which will dampen especially low-frequency sounds, the MOCR by reducing the responsiveness of the outer hair cells), so that any quieter sound has a better chance of getting heard (or is getting
"de-masked").
118
When do the 2 antimasking reflexes work best
both reflexes are effective in different (but slightly
overlapping) frequency ranges - the MEMR works better at lower frequencies 20-1000 Hz while the MOCR works better at higher frequencies, conveniently starting at about 1 kHz
119
How does the medial olivocochlear system control cochlear mechanics
What would this require?
(i) Change the stiffness of the stereocilia or
(ii) Actively displace the stereocilia, introducing a
bias in their displacement
the cochlea to signal any changes in its
state to the brain
120
What may signal changes in the state of the cochlear to the brain after it has been affected by the medial olivocochlear system
The type II auditory nerve
| fibres (connecting with the OHCs)
121
What is the purpose of the Medial olivocochlear system changing the cochlear mechanics
to keep the
| cochlea in its optimal mechanical state.
122
What is the reason for the auditory pathway being more complex than the visual pathway between the receptor and cortex
the need to compute the
localisation of a sound source from the receptor
epithelium which is tonotopically and not
spatially organised
123
What is the cochlear nucleus
an
obligatory synapse for all auditory-nerve fibres
and has been described as the ‘retina of the
auditory system’.
124
where does most parallel processing in the auditory system occur
cochlear nucleus
125
Which cells are characterised by large end-bulb of Held synapses
cells in the cochlear nucleus specialised to
preserve the timing information present in the
auditory nerve input.
126
What are the largest synapses in the brain
end-bulb of Held synapses
127
Describe the different types of cells at the cochlear nucleus
timing preservation cells
intensity encoding cells
laterally inhibiting cells
128
Describe the intensity encoding cells of the cochlear nucleus
have a dynamic range considerably
wider that found in any individual auditory nerve
fibre;
cells at this stage are summing
129
Are any auditory pathway responses preserved as high as the cortex?
While much of the cochlear output may be
modified by the cochlear nucleus and higher
levels in the auditory pathway many response
properties of auditory-nerve fibres e.g.
tonotopicity, are preserved at levels as high as
the cortex
130
Where is the first site of binaural convergence of the cochlear nucleus output?
```
the superior
olivary complex (SOC)
```
131
Describe the STRUCTURE OF THE SOC
There are three main
SOC nuclei; the lateral superior olive (LSO), the
medial superior olive (MSO) and the medial
nucleus of the trapezoid body (MNTB or MTB)
132
What does the auditory midbrain consist of
the inferior
| colliculus (IC) and the superior colliculus (SC).
133
Describe the function of cells in the inferior colliculus
spatially selective, but no map of auditory space has been found in this nucleus.
134
Describe the function of cells in the superior colliculus
a map of
auditory space does exist in the deep layers of
the superior colliculus and is usually aligned with
a visual map of space
135
How is the primary auditory cortex (A1) organised
tonotopically organised and is
bordered by one or more adjacent auditory
areas.
136
What is the function of the mammalian auditory cortex
no idea
137
How is auditory space mapped on the basilar membrane
IT IS NOT
138
How well can we discriminate the location of sounds in azimuth and in elevation
2°apart
in azimuth (or horizontal plane) and 10° apart in
elevation (or vertical plane)
139
How does the intensity of a sound change with distance
How does this help most mammals calculate distance?
intensity of a sound decreases with distance
(amplitude decreases by a factor of 2, or 6 dB,
with a doubling of distance)
we are unable to use
intensity as a cue for calculating distance. We
would need to know the level of the source for
this to be a useful cue
140
Can humans use intensity to localise sound?
- in fact we are able to do
this with limited success with human speech as
we are so familiar with it
141
Can you localise sound with one ear?
While sound
localisation is possible with one ear better
results are obtained by combining information
from the two ears. The brain can compare the
differences in both time and intensity of a sound
arriving in both ears.
142
Which is the only location that sound travels equal distance to reach either ear
0° azimuth
143
What is the maximum time difference between sound hitting one ear and the other in humans
What location would this occur at
660 microseconds
90° & 270° azimuth
144
What is the minimum interaural time difference
10 microseconds
145
How can interaural phase differences provide a cue for localisation
For continuous sounds below
| about 1.4 kHz
146
Why is 1.4kHz the limit for use of interaural phase difference in localisation
the
size of the head causes phase to become
ambiguous.
147
Give an overview of neural encoding of interaural time differences
The MSO receives input from spherical bushy
cells of the anteroventral cochlear nucleus from
both sides of the brain and uses the
principles of coincidence detection and delay
lines to measure interaural time differences in
different frequency bands.
148
What is the concept of delay lines? (4)
| better described visually so there is also an anki card on this
neurons fire maximally when action potentials from the left and right ear arrive simultaneously.
Each neuron is maximally sensitive to a single time disparity (best ITD) and
different neurons are selective for different
disparities.
The axonal path to the neurons increases systematically along the array but in the opposite direction for the two ears.
Therefore, the place of a neuron in the MSO
signals the ITD to which the neuron responds best
149
How can interaural intensity differences be used in localisation
At high frequencies the more distant of the two
ears is shadowed by the head and the sound
reaching this ear is less intense.
150
What is the range for interaural intensity differences
The interaural
intensity difference is insignificant below about
1 kHz and reaches a maximum of about 20 dB for
high frequencies at 90° and 270°azimuth
151
Describe the neural pathway to encode interaural intensity differences (give both inhibitory and excitatory pathways)
The LSO receives excitatory input from bushy
cells in the ipsilateral VCN and inhibitory input
from the ipsilateral MNTB.
The ipsilateral MNTB
receives excitatory input from the bushy cells of
the contralateral VCN
152
What are cells in the MNTB characterised by
what does this allow
giant synaptic
endings allowing for the fast, precise
transmission of temporal information
153
What does output of neurons in the LSO reflect in the hearing system?
the balance of ipsilateral excitation and contralateral inhibition
154
For pure tones, what does localisation in the azimuthal plane depend upon
interaural time differences at low frequencies
and interaural intensity differences at high
frequencies
155
for pure tones it appears that
localisation in the azimuthal plane depends on
interaural time differences at low frequencies
and interaural intensity differences at high
frequencies
What is this known as?
duplex theory
