11: Introduction to the Auditory System Flashcards
(97 cards)
1
Q
Define physical and perceptual sound.
A
Physical: pressure changes in the air (or other physical medium).
Perceptual: the experience of hearing.
2
Q
Briefly, describe the process in which we hear vibrations.
A
Object vibrates → air molecules vibrate → eardrum vibrates.
3
Q
Air molecules are _____ in regions of higher pressure and _____ in regions of lower pressure.
A
Closer together; farther apart.
4
Q
Air molecules farther apart are what?
A
Rarefied.
5
Q
Air molecules closer together are what?
A
Condensed/compressed.
6
Q
The simplest sound waves are what?
A
Pure tones.
7
Q
How is frequency calculated?
A
Frequency = 1/t (Hz)
8
Q
What is amplitude? How do we perceive it?
A
Difference in pressure between high and low peaks of wave. Perception is loudness.
9
Q
What is used as a measure of amplitude? What is its equation?
A
Decibel (dB).
Number of dB = 20 × log10(p/po)
10
Q
The logarithmic nature of the decibel maps nearly linearly to _____ using _____.
A
Perceived loudness; magnitude estimation.
11
Q
List the relative amplitudes and decibels for the following environmental sounds:
Barely audible (threshold) Leaves rustling Quiet residential community Average speaking voice Express subway train Propeller plane at takeoff Jet engine at takeoff (pain threshold) Spacecraft launch at close range
A
Barely audible (threshold): 1 / 0dB
Leaves rustling: 10 / 20dB
Quiet residential community: 100 / 40dB
Average speaking voice: 1,000 / 60dB
Express subway train: 100,000 / 100dB
Propeller plane at takeoff: 1,000,000 / 120dB
Jet engine at takeoff (pain threshold): 10,000,000 / 140dB
Spacecraft launch at close range: 100,000,000 / 160dB
12
Q
What are hertz (Hz)? What are they used for?
A
Cycles per second, used to measure frequency.
13
Q
Frequency is linked to the perception of _____.
A
Pitch.
14
Q
What is tone height?
A
Perceptual experience of increasing pitch as sound frequency increases.
15
Q
On a keyboard, the notes A, B, C, D, E, F, G repeat, and notes of the same letter sound similar. Notes of the same letter have the same _____.
A
Tone chroma.
16
Q
Musical notes are described in _____.
A
Octaves.
17
Q
For each octave increment the frequency is _____.
A
Doubled.
18
Q
Notes of the same tone chroma have frequencies that are _____.
A
An octave apart.
19
Q
Range of hearing is affected by what two things?
A
Frequency and intensity.
20
Q
Which animal can hear the highest frequencies? The lowest?
A
Highest: dolphins.
Lowest: elephants.
21
Q
In terms of physical dimension and perceptual dimension, amplitude equals _____, frequency equals _____, and complexity equals _____.
A
Loudness; pitch; timbre.
22
Q
All other properties of sound except for _____ and _____ constitute timbre.
A
Loudness; pitch.
23
Q
Most of our auditory experience is of what?
A
Complex tones.
24
Q
Define additive synthesis.
A
Multiple frequencies make up complex tones.
25
Musical tones have additional harmonics that are _____.
Multiples of the fundamental frequency.
26
What is the effect of the missing harmonic?
Removing fundamental frequency does not change perceived pitch (although the timbre does change).
27
Define periodicity pitch.
Perceived similarity of tones that have harmonics removed.
28
Buildup of sound at the beginning of a tone?
Attack of tones.
29
Decrease in sound at end of tone?
Decay of tones.
30
Outline the features of the outer ear, middle ear, and inner ear.
Outer ear: pinna(e), auditory canal, tympanic membrane (eardrum).
Middle ear: ossicles, oval window, middle ear muscles.
Inner ear: cochlea (anatomy and function).
31
What is the part of the ear on the outside of the head?
Pinna(e).
32
The auditory canal uses resonance. Explain and specify what range of sound it amplifies.
Sound waves reflected off the tympanic membrane create constructive interference with incoming waves.
Amplifies sounds in 2-5 kHz range.
33
At the end of the auditory canal, what borders between the outer ear and middle ear?
Tympanic membrane (eardrum).
34
In the ossicles, what three bones make up it? What is distinct about them in relation to the human body?
Malleas, incus, stapes.
Smallest bones in the human body.
35
What do the middle ear muscles do? What is distinct about them?
At high intensities they dampen the vibration of the ossicles.
Smallest skeletal muscles in the human body.
36
The ossicles concentrate vibration on a smaller surface area, which increases the pressure per unit area by a factor of what?
~17
37
The ossicles act as levers, thereby increasing the vibration by a factor of what?
~1.3
38
Why is physical amplification of sound by the middle ear required?
Pressure changes in air (outer and middle ear) are transmitted poorly to liquid (the cochlear fluid).
39
Fish do not have middle and outer ear structures. Why?
Do not need to amplify sounds as greatly since water and cochlear fluid have similar densities.
40
The stirrup vibrates against membrane behind _____.
Oval window.
41
A particular region of the basilar membrane _____ in response to sound of a particular frequency.
Flexes back and forth.
42
The cochlea is a fluid-filled structure split into two parts by the cochlear partition. What are these two parts?
Scala vestibuli: extends from the oval window at the cochlea’s base to the apex.
Scala tympani: extends from the apex to the round window at the cochlea’s base.
43
What is the site of sound transduction into neural activity? Where is it located?
Organ of Corti. Located in scala media.
44
How many inner and outer hair cells are there?
3,500 inner; 12,000 outer.
45
Hair cells are connected to fibers which leave the cochlea as _____.
The auditory nerve.
46
Inner hair cells _____ and each connects to _____ auditory nerve fibers.
Diverge; 8-30.
47
Outer hair cells _____ and each auditory nerve fiber is connected to _____.
Converge; many outer hair cells.
48
Hair cells have what? How do they influence the transduction process?
Cilia.
When they bend, transduction process starts.
49
Stapes vibrates → oval window vibrates. What does this cause?
Pressure changes in cochlear fluid.
50
Stapes vibrates → oval window vibrates. The basilar membrane vibrates at the same frequency as _____.
The stapes.
51
Stapes vibrates → oval window vibrates. The _____ moves back and forth
Tectoral membrane.
52
The cilia of the outer hair cells are embedded in the _____.
Tectoral membrane.
53
When the _____ vibrates, the hair cells bend.
Basilar membrane.
54
What does depolarization and hyperpolarization do to the basilar membrane?
Depolarization: increased impulse frequency.
Hyperpolarization: decreased impulse frequency.
55
Endolymph (+80mV) has a very high _____ concentration.
K+.
56
What are the resting potentials for outer hair cells and inner hair cells?
Outer hair cells: -70mV
Inner hair cells: -40mV
57
When tip links physically link one cilia to another, what happens?
Cadherin23 strand connects two TRPA1 channels, creates a mechanically gated ion channel.
58
At rest, TRPA1 gates are _____.
Partially open.
59
Deflection of cilia towards the _____ pulls the TRPA1 gates open more. Deflection of cilia towards the _____ relaxes the tip links, allowing the TRPA1 gates to close fully.
Long-side; short-side.
60
Describe how endolymph depolarizes hair cells.
K+ moves into the cilia based on electrical gradient alone, influx depolarizes the cell which activates voltage-gated Ca2+ channels, Ca2+ triggers exocytosis of neurotransmitters.
61
The cochlea acts as a hydrodynamical frequency analyzer. What two things allow this? What also contributes
Passive mechanical properties; active mechanics of the outer hair cells.
Phase locked firing of neurons also contributes.
62
Stiffness in the basilar membrane decreases with distance from _____.
The base.
63
In the basilar membrane, what progressively slows until the wave essentially stops with all the energy “piling up” at a particular characteristic location?
Acoustic energy propagation.
64
Each location in the basilar membrane has a _____ largely determined by the _____.
Characteristic frequency; membrane stiffness.
65
The characteristic frequency decreases as stiffness decreases. Therefore, base and apex must equal what?
Base = high frequencies.
Apex = low frequencies.
66
The propagation of the acoustic energy along the basilar membrane can be summarized by the _____.
Envelope of the traveling wave.
67
The peak of the envelope occurs at what?
A different place for each frequency.
68
Hair cells are most perturbed at the _____ of the envelope. Therefore, frequency can be coded neuronally as the location of _____ on the basilar membrane.
Peak; peak deflection.
69
The cochlea acts like a filter for what tones?
Simple and complex.
70
The basilar membrane is a frequency analyser. What is it sometimes called?
Auditory prism.
71
When you record electrical activity of auditory nerve or individual hair cells, you get what?
Tonotopic map: an ordered map of characteristic frequencies along the length of the cochlea.
72
Recordings from single auditory nerve fibers found what three things?
Characteristic frequency (CF) point on curve with lowest threshold.
CF changes in an orderly manner moving from the base to the apex.
Curves become wider at higher frequencies (with linear x-axis).
73
How is the bionic ear (cochlear implant) possible?
Tonotopic map in cochlea. Electrical stimulation bypasses damaged hair cells.
74
Von Bekesy’s model of the cochlea predicts poor discrimination between similar tones. Yet, psychophysical evidence shows that we are good at distinguishing tones of similar frequencies. Name two pieces of this evidence.
Living basilar membranes show sharper peaks in their vibrational envelopes than previously measured from cadavers.
The cochlea can emit sound (otoacoustic emissions).
75
Healthy basilar membranes show that the outer hair cells respond to sound by changing length. This is called the _____.
Motile response.
76
In the cochlea, inner hair cells carry _____, outer hair cells provide the _____.
Sound information; motile response.
77
Motile response is triggered by what two things?
Deflection of the cilia and central feedback.
78
Upon depolarization, _____ unbind Cl- and contracts.
Prestin protein.
79
Motile response _____ and _____ of the basilar membrane. It is sometimes called the _____.
Reinforces; shapes vibrations; cochlear amplifier.
80
What two codes allow us to code for frequency (pitch)?
Place code: neurons on basilar membrane code different frequencies.
Timing code: the frequency of the sound is reflected in the firing of neurons.
81
Define phase locking.
The firing of neurons in synchrony with the phase of the stimulus.
82
Why can't a single neuron fire quickly for, say, 700Hz?
Absolute refractory period.
83
Why can't pitch perception be as simple as the place theory?
Periodicity pitch.
84
Fundamental frequency can still be determined by what two things?
Modified place code: separation of harmonics on cochlea.
Temporal coding: timing of neural firing.
85
Pitch perception mostly occurs for frequencies below 5000Hz, which is the also the limit of phase locking. What does this suggest?
Temporal coding is probably the main determinant of pitch perception.
86
Fundamental plus lower harmonics activate different _____. Higher harmonics activate _____.
Filters; multiple overlapping filters.
87
The sum of filter activity is known as what?
Excitation pattern.
88
Define resolved and unresolved harmonics and their effect on perception of pitch.
Resolved: produce peaks in the excitation pattern. Produce strong perception of pitch.
Unresolved: produce smooth activity in excitation pattern. Produce weak perception of pitch.
89
A1 in the auditory cortex has what type of organization?
Columnar.
90
Neurons in same A1 column have the same _____.
Characteristic frequency.
91
Lesion studies in monkeys on A1 show what?
Monkeys can learn to discriminate pure tones even when auditory cortex is lesioned.
92
In pre-cortical nuclei, what is enough for pure tone discrimination?
Tonotopy.
93
Marmoset pitch neurons do what?
Respond to characteristic frequency or periodicity pitch stimuli.
94
fMRI of pitch representation in humans used 2 kinds of stimuli that had the same frequency range. What happened with resolved and unresolved harmonics?
Resolved: evokes pitch perception.
Unresolved: does not evoke pitch perception.
95
Areas most responsive to pitch (prefer resolved harmonics) are located where?
Anterior auditory cortex.
96
Describe hearing loss with regards to damage to outer and inner hair cells. What happens?
Outer hair cell damage (more common): basilar membrane peak becomes shorter and broader, loss of sensitivity and difficulty discriminating sounds.
Inner hair cell damage: generalized cell loss → decreased sensitivity. Specific region along basilar membrane → "dead zone."
97
What is presbycusis? What accelerates it?
"Old ear." Cumulative effect of hair cell damage over a lifetime of noise.
Can be accelerated by ototoxic drugs (e.g. certain antibiotics or diuretics), loud noises (leisure, workplace, etc.).
