Hearing

Question 1

What will an oscillating object cause the air to do?

Answer 1

become more and less dense = compression and rarefaction

Question 2

What are radiating waves?

Answer 2

sound waves that come outwards from the source

Question 3

How do you calculate wavelength?

Answer 3

velocity divided by frequency

Question 4

How do you define amplitude?

Answer 4

Measured in decibels
Mechanism for describing the intensity of sound
Amplitude is generally expressed as a ratio

Question 5

What is the range of human hearing? and what happens to this as you get older?

Answer 5

freq = 20-20 000 Hz
As you get older your high end range gets affected and becomes lower
amplitude - 0-140 dB

Question 6

Sometimes sound pressure levels are adjusted using “A weighting”. what does this do? how will a high freq sound then compare to a low freq sound that are the same volumes?

Answer 6

Down-scales low frequencies to acknowledge our lower sensitivity
A higher freq sound will appear louder than the low freq sounds due to us being more sensitive to the higher frequency sound

Question 7

Explain the role of the tuning curve

Answer 7

• this is for the auditory nerve fibres

For any given auditory nerve cell, it has a preferential frequency to activate the cell

Question 8

What is the role of the ossicles (bones in the middle ear)

Answer 8

1. Tympanic membrane deflects
2. Middle ear bones move
3. Membrane in oval window moves
4. Basilar membrane moves
5. Round window - allows fluid to move back and forth

Question 9

What does the middle ear do?

Answer 9

acts as a lever

it converts high amp & low force motion to the ear drum into low amp & high force motion at the oval window

Question 10

what is the stapedius reflex and what do they do?

Answer 10

• 2 muscles that act on the ossicles
• the contraction of these muscles pulls stapes away from the oval window. this decreases the transmission of vibrational energy to the cochlea . Stapedius reflex occurs in response to very loud sounds.
  Also occurs during speech
  Crucial for preventing hearing damage

Question 11

What is the cochlea made up of?

Answer 11

round window
3 scalae –> 1. Scala vestibulae 2. Scala media 3. Scala tympani
Helicotrema

Question 12

what is the organ of corti? where is it in the cochlea?

Answer 12

it is embedded in the Basilar membrane in between the scala vestibulae and the scala tympani
it has inner hair cells sensation and outer hair cells motors (presin - a protein that is capable of contracting)

Question 13

how are the hair cells of the organ of corti activated?

Answer 13

Small up-down movements of the basilar membrane cause a large relative shear of the tectorial membrane, thus activating the hair cells and causing hyper or hypo polarisation depending on which way it is going.

Question 14

How does you ear distinguish between different frequencies of sound?

Answer 14

1. Pitch place theory

2. The ear is a fourier analyser

Question 15

Explain the pitch place theory

Answer 15

different freqs of sound will be coded at different places along the basilar membrane in the cochlea. it will cause vibrations at certain points

• high frequency= oscillations at the lower end of the cochlea where the membrane is tort and stiff.
• low frequency - oscillations at the other end of the cochlea where the membrane is more loose
• Different frequencies of sounds are coded by different neurons along the auditory nerve

Question 16

Explain how the ear is a fourier analyser

Answer 16

any waveform can be decomposed into sine waves of various frequencies
even a square wave can be made up of sine waves: combine the fundamental frequency with progressively smaller harmonics

Question 17

where does amplification happen in the ear?

Answer 17

the active outer hair cells by positive feedback

Question 18

outer hair cells can generate sound

Answer 18

otoacousitic emissions are echos in response to clicks delivered to the ear.
Absence of this indicates a problem of the inner ear. therefore this is used to assess hearing in newborns
It is also a possible mechanism for some types of tinnitus.

Question 19

hearing is most sensitive to which frequencies?

Answer 19

Speech freqs

which are at 400-3000 Hz

Question 20

What is noise induced hearing loss that is:
1. Temporary
2. Permanent
called?

Answer 20

1. Temporary Notch. Anything over 85 dB is potentially damaging
2. Permanent sensorineural defect

Question 21

What is the auditory pathway in the brain?

Answer 21

Sound activates many areas from the cochlear nerve to the auditory cortex. It also includes the superior olive (brainstem)

Question 22

Why is it important to localise sounds?

Answer 22

• To know where other player are on the pitch and where to pass to etc

Question 23

What is the cocktail party effect?

Answer 23

we can understand conversation from an individual speaking among many others. It involves localisation cues as well as vision.

Question 24

Judging distance. High frequency sounds travel less well; far away sounds are dominated by bass.
Expectations eg intensity of voice
Relative attenuation of certain types of sound… what travels best? worst?
Echoes give us lots of cues

Answer 24

Bass travels best

sibilants travel worst

Question 25

What are the 3 techniques in which we judge direction?

Answer 25

1. inter arual timing / phase differences
2. Inter-aural volume differences
3. Spectral colouring by the pinna & head

Question 26

Explain the concept of Interaural time delay (ITD).

How accurate is this?

Answer 26

a click from the left will arrive at the left ear before the right ear.
It is accurate to one degree

Question 27

what is jeffress theory of ITD detection?

Answer 27

Neurons in the superior olive act as coincidence detectors.
When action potentials arrive simultaneously from both ears, MSO neuron is more likely to fire.
It relies on differing lengths of axons.
provides a neuronal map of sound location

Question 28

When would you use inter-aural phase differences?

Answer 28

If sound is a continuous tone, you use phase difference to localise it. Its not very useful when the wavelength is shorter than the head (ie a high frequency sound)

Question 29

Explain how inter-aural volume differences works

Answer 29

the head provides a sound shadow. Reduces volume in the ear opposite the sound source.
There is greater reduction for high frequency sounds, hence far away speech is more bassy.

Question 30

explain the role of spectral colouring by the pinna and head

Answer 30

The pinna (outer ear) reduces sounds from certain directions and amplifies sound from other.
Invisible to low frequency sounds (bass)
Therefore, the spectral content of sound combined with prior experience, can be used for localisation.

Question 31

Why does head size matter?

Answer 31

big head = large left/right time difference. small head = not so much.
BIg heads will use timing inter-aural differences. Small heads will use loudness differences.

Smaller heads are better at detecting high frequency sounds

Question 32

Explain the role of the cone of confusion

Answer 32

sounds coming from 2 different places can produce identical interaural level differences (ILD) and ITD (timing) profiles and the 2 ears.

• eg sounds coming from behind the head can sometimes seem like they’re coming from in front.
• Tilting and turning the head alters the cone of confusion

Question 33

What are the auditory time reaction values?

Answer 33

140-160 ms

sound takes 3ms per metre

Question 34

What is the startle response? Whats it evoked by?

Answer 34

Evoked by loud sounds at about 120 dB
evokes a blink at 40ms and a neck contraction at 80ms.
It is too fast to involve the cerebral cortex. and is mediated by the brainstem