Week 2- Audition Flashcards
1
Q
What is sound
A
A wave of pressure variations
2
Q
What are sound waves
A
A wave of compression and rarefaction, by which sound is propagated in a elastic medium such as air.
3
Q
What is compression
A
Where molecules are forced or pressed together, it is a wave where the particles are closest together
4
Q
What is rarefaction
A
Rarefaction is the opposite of compression, it is when the molecules are given extra space and allowed to expand.
It is the wave where the particles are furthest apart.
5
Q
What are the properties of a wave
A
Frequency, amplitude and phase
6
Q
What is frequency
A
how many full waves in a second? (Hz) corresponds to the pitch of the sound
7
Q
What is Amplitude
A
how high is the wave? (dB) corresponds to the loudness of the sound
8
Q
What is Phase
A
How far through the wave are we? (degrees) corresponds to the timbre of the sound
9
Q
What is fourier analysis
A
The breaking down of a complex wave into its sine wave components
10
Q
What is complex sounds
A
When sounds of different frequencies are added together
11
Q
What is pure tone
A
A tone with one frequency, a sine wave
12
Q
What are natural sounds
A
Simple sine waves added together
13
Q
What makes up the outer ear
A
The Pinna and Meatus
14
Q
What does the Pinna do
A
The pinna in humans colours high frequency sound by interference between the echoes reflected in different structures.
Only frequencies that have a wavelength comparable to the dimensions of the pinna are influenced by it. The direction of sound is important.
15
Q
What is the meatus
A
The tube that links the pinna to the eardrum
16
Q
What makes up the middle ear
A
Tympanic membrane, malleus, incus and stapes
17
Q
What are the two functions of the middle ear?
A
- the middle ear helps turn large amplitude vibrations in air to small aptitudes vibration in fluid.
- it protects against loud low frequency sounds through the stapedius reflex
18
Q
What makes up the inner ear?
A
The cochlea
19
Q
How many chambers are in the cochlea?
A
3
20
Q
What are two of the chambers in the cochlea separated by?
A
The basilar membrane.
21
Q
What does the basilar membrane sit on?
A
The organ of Corti
22
Q
What sits on top of the organ of corti?
A
The tectorial membrane
23
Q
What is the tectorial membrane/
A
Sound travels on here moving the inner hair cells
24
Q
What makes up the organ of corti
A
Inner hair cells
25
What is the basilar membrane function
Sound travels on here moving the inner hair cells
26
What is the place code for frequency
```
Low frequency (wide and floppy) tones make the whole basilar membrane vibrate at the frequency of the tone. High frequency tones peak near the base of the membrane, thin and narrow.
When there is more than one tone, their vibrations add together
```
27
What is characteristic frequency?
Characteristic frequency (CF) of a particular place along the membrane is the frequency that peaks at that point
28
What is frequency tuned auditory filters?
“Frequency-tuned auditory filters” If 10,000 Hz i the characteristic frequency of a nerve fibre, it will still respond to frequencies a little bit above and below that number.
29
What are the limits of what we dont hear
below 20Hz and above 20000 Hz
30
What is a frequency code
the auditory nerve also encodes cells depending on how many times it fires for each sound. When an impulse is generated, a single nerve impulse is generated and this is called firing of the nerve. This firing of the nerve also encodes frequency information, according to the frequency of the sound.
31
What is phase locking
the chemical process is timed with how the auditory nerve fires. This principle only works for low frequencies because of the refractory period
32
What is transduction
* As the hairs of inner hair cells bend, the voltage of the hair cell changes
* When the hairs are bent sufficiently in one direction, the voltage realises a neurotransmitter b/w the hair cell and the auditory cell synapse - the auditory nerve fires
* After firing the auditory nerve fibre has a refractory period of around 1 ms
33
How does coding intensity differ
•each nerve has a resting state in which it continuously fires “spontaneous firing rate of a nerve”, it’s only when you hear a sound that the firing rate increases. That’s how they ‘code’ for the sounds.
* sounds at lower intensity have the high spontaneous rate fibres coding for them. These are the fibres that would increase their firing rate and help code the information.
* if you have a high sound, you don’t want it to saturate so soon. This is why you have low spontaneous rate fibres.
34
What are our two nerve fibres
Low and High spontaneous rates.
| Low fires slowly and high fires faster
35
How much can each fibre code for?
Between 20-50 dB of change
36
What is a low pass filter
Filter allows really low frequencies to get through
37
What is a high pass filter
Only allows high pass frequencies to get in
38
What are our auditory filters?
Band filters
39
What is a band filter?
Allow a band of frequencies to pass through, Have a high cut off frequency and a low.
40
What are the three steps to apply fourier theory?
1. output of filter must not contain any frequency which was not present in input
2. if amplitude of input is changed by some factor, the output must also change by the same factor
3. output of A+B+C must be equal to output of (A) + output (B) + output (C)
41
What are filters that violate the three step rule for fourier theory called?
Non linear filters
42
What are the reasons that the ear is a fourier analysis?
* it helps break up a complex sound into sine waves - there are auditory filters along the baslar membrane, high frequency sounds responded to by the base & low frequency sounds responded to by the apex
* responds to amplitude to each of these corresponding sine waves
* can encode phase information
43
What are the reasons against fourier analysis
* goes against (1) - two tones should result in separate peaks but often the peaks merge (“two tone suppression”)
* sometimes the ear introduces distortion products - if the ear generates two frequencies close together then the ear will generate extra frequencies (Otoacoustic emissions). These are frequencies that were not generated in the input but occur in the output.
* violates the role of the outer hair cells. The function of the outer hair cells, it helps to amplify small intensities. If there are sounds that have really low intensities the outer hair help amplify it by their movement & help the encoding to happen.
44
Where do auditory nerve fibres terminate?
In the cochlea nucleus
45
Where is the cochlea nucleus located
At the brain stem
46
What do binaural neurons do?
Help consolidate information from the two ears
47
What does tonotopically organised mean?
Organised in terms of sound frequency
48
Where do outer hair cells get their input?
From the brain
49
What do outer hair cells do?
They help encode information by changing their length and change the attributes of the signal encoding.
50
What is the descending auditory pathway?
• descending fibres run from auditory cortex to cochlea, with synapses in reverse order to ascending projections
51
What are efferent pathways and afferent pathways?
Efferent pathways helps to encode sound and the afferent pathway negates how the sounds are encoded
52
What is the basilar membrane function
Sound travels on here moving the inner hair cells
53
What is the place code for frequency
```
Low frequency (wide and floppy) tones make the whole basilar membrane vibrate at the frequency of the tone. High frequency tones peak near the base of the membrane, thin and narrow.
When there is more than one tone, their vibrations add together
```
54
What is characteristic frequency?
Characteristic frequency (CF) of a particular place along the membrane is the frequency that peaks at that point
55
What is frequency tuned auditory filters?
“Frequency-tuned auditory filters” If 10,000 Hz i the characteristic frequency of a nerve fibre, it will still respond to frequencies a little bit above and below that number.
56
What are the limits of what we dont hear
below 20Hz and above 20000 Hz
57
What is a frequency code
the auditory nerve also encodes cells depending on how many times it fires for each sound. When an impulse is generated, a single nerve impulse is generated and this is called firing of the nerve. This firing of the nerve also encodes frequency information, according to the frequency of the sound.
58
What is phase locking
the chemical process is timed with how the auditory nerve fires. This principle only works for low frequencies because of the refractory period
59
What is transduction
* As the hairs of inner hair cells bend, the voltage of the hair cell changes
* When the hairs are bent sufficiently in one direction, the voltage realises a neurotransmitter b/w the hair cell and the auditory cell synapse - the auditory nerve fires
* After firing the auditory nerve fibre has a refractory period of around 1 ms
60
How does coding intensity differ
•each nerve has a resting state in which it continuously fires “spontaneous firing rate of a nerve”, it’s only when you hear a sound that the firing rate increases. That’s how they ‘code’ for the sounds.
* sounds at lower intensity have the high spontaneous rate fibres coding for them. These are the fibres that would increase their firing rate and help code the information.
* if you have a high sound, you don’t want it to saturate so soon. This is why you have low spontaneous rate fibres.
61
What are our two nerve fibres
Low and High spontaneous rates.
| Low fires slowly and high fires faster
62
How much can each fibre code for?
Between 20-50 dB of change
63
What is a low pass filter
Filter allows really low frequencies to get through
64
What is a high pass filter
Only allows high pass frequencies to get in
65
What are our auditory filters?
Band filters
66
What is a band filter?
Allow a band of frequencies to pass through, Have a high cut off frequency and a low.
67
What are the three steps to apply fourier theory?
1. output of filter must not contain any frequency which was not present in input
2. if amplitude of input is changed by some factor, the output must also change by the same factor
3. output of A+B+C must be equal to output of (A) + output (B) + output (C)
68
What are filters that violate the three step rule for fourier theory called?
Non linear filters
69
What are the reasons that the ear is a fourier analysis?
* it helps break up a complex sound into sine waves - there are auditory filters along the baslar membrane, high frequency sounds responded to by the base & low frequency sounds responded to by the apex
* responds to amplitude to each of these corresponding sine waves
* can encode phase information
70
What are the reasons against fourier analysis
* goes against (1) - two tones should result in separate peaks but often the peaks merge (“two tone suppression”)
* sometimes the ear introduces distortion products - if the ear generates two frequencies close together then the ear will generate extra frequencies (Otoacoustic emissions). These are frequencies that were not generated in the input but occur in the output.
* violates the role of the outer hair cells. The function of the outer hair cells, it helps to amplify small intensities. If there are sounds that have really low intensities the outer hair help amplify it by their movement & help the encoding to happen.
71
Where do auditory nerve fibres terminate?
In the cochlea nucleus
72
Where is the cochlea nucleus located
At the brain stem
73
What do binaural neurons do?
Help consolidate information from the two ears
74
What does tonotopically organised mean?
Organised in terms of sound frequency
75
Where do outer hair cells get their input?
From the brain
76
What do outer hair cells do?
They help encode information by changing their length and change the attributes of the signal encoding.
77
What is the descending auditory pathway?
• descending fibres run from auditory cortex to cochlea, with synapses in reverse order to ascending projections
78
What are efferent pathways and afferent pathways?
Efferent pathways helps to encode sound and the afferent pathway negates how the sounds are encoded
