L24 Hearing And The Brain

Question 1

What happens when the outer hair cell amplifier is damaged?

Answer 1

The nerve fibre is less sensitive and has poorer tuning

Question 2

What does poor tuning effect?

Answer 2

Affects speech intelligibility, particularly in noisy situations
- sounds are more blurred

Question 3

What happens to nerve fibres when sound gets louder?

Answer 3

Fibres respond to a broader range of frequencies

Question 4

What do sound with frequencies and levels within the shaded area drive?

Answer 4

Drive the nerve fibre above background rate

Question 5

What is tonotopic organisation?

Answer 5

Throughout the auditory pathway sound frequencies is mapped within the processing centres and on the surface of the auditory cortex

Question 6

What do auditory systems keep track of?

Answer 6

Where info is originated on the basilar membrane (beginning with nerve fibre)

Question 7

What is time code?

Answer 7

• the firing of APs in auditory nerve fibres synchronise with peaks of sound waveform
• phase locking
• time between APs tells us about the freq of sound
• only occurs for low freq sound (below 3-5 kHz)
• probably the basis for musical pitch

Question 8

What is phase locking?

Answer 8

When firing is locked or synchronised to a particular phase of sound waveform

Question 9

Outline the human auditory pathway

Answer 9

1. Cochlea
2. Auditory nerve - connects cochlea to brain
3. Ventral cochlea nucleus - first synapse
4. Superior olive
5. Lateral lemniscus
6. Inferior colliculus (midbrain)
7. Medial geniculate body (thalamus)
8. Auditory cortex (temporal lobe)

Predominantly contralateral
Crosses at the superior olivary complex

Question 10

What is the vertical plane in sound localisation?

Answer 10

Interactions of sound on the pinna (outer ear)

Question 11

What is the horizontal plane in sound localisation?

Answer 11

Interaural (between the ears) differences in sound wave timing and intensity

Question 12

List some cues for sound localisation in the horizontal plane

Answer 12

• position of sound not represented on basilar membrane in the cochlea
• need to compute location of sound by comparing inputs from two ears
• sounds in different positions in space lead to timing and intensity differences at the ears

Question 13

What are the two interaural timing cues?

Answer 13

1. For all sounds
   - differences in sound onset time between the two ears
   - except when in front or behind the listener
2. For long continuous sounds
   - difference in phase of sound between ears

Question 14

How are high frequencies localised by interaural intensity differences?

Answer 14

• the head casts a sound shadow for high freq
• the brain detects a difference in sound intensity between the ears
• this difference changes as position of sound source

Question 15

What happens to a long wavelength that is relative to an obstacle?

Answer 15

They get diffracted
- the waves bend around the head and join up of the far side with no sound shadow