4e. Sound Localisation

Question 1

Sound Localisation

- Degrees

Answer 1

2 degrees azimuth

10 degrees elevation

Question 2

Maximum Detectable Interaural Time Difference

Answer 2

660 microseconds

Question 3

Minimum Detectable Interaural Time Difference

Answer 3

10 microseconds

Question 4

Interaural Time Difference

- Frequency

Answer 4

Can be used for localisation of continuous sounds below 1.4kHz, where phase becomes ambiguous

Question 5

End Bulb of Held Synapse

- Function

Answer 5

Preserve temporal information of phase-locking

Question 6

End Bulb of Held Synapse

- Structure

Answer 6

Auditory nerve fibre enveloping a cell form the ventral cochlear nucleus, which is a spherical bushy cell

Question 7

End Bulb of Held Synapse

- Locations

Answer 7

• Anterior ventral cochlear nucleus (AVCN)
• Medial nucleus of the trapezoid body (MNTB)
• Ventral nucleus of the lateral lemniscus

Question 8

End Bulb of Held Synapse

- Action Potential Components

Answer 8

1. Presynaptic potential (PP) from the large end-bulb
   - Excitatory post synaptic potential (EPSP)
   - Somatic action potential (SAP)

Question 9

Interaural Time Difference

- Neural Pathway

Answer 9

1. Cochlea
2. Anterior ventral cochlear nuclei (AVCN)
3. Spherical bushy cell
4. Ventral stria (trapezoid body)
5. Medial superior olive (MSO)

MSO receives information from both AVCNs, which meet in the same cell

Each MSO is tuned to localise sound coming from the direction of the contralateral ear

Question 10

Interaural Time Difference

- Neural Analysis

Answer 10

Cell in the medial superior olive (MSO) uses coincidence detection and delay lines to measure the intramural time differences

Gives a labelled line scheme encoding azimuth

Question 11

Maximum Interaural Intensity Difference

Answer 11

20dB

Question 12

Interaural Intensity Difference

- Neural Pathway

Answer 12

1. Cochlea
2. Anterior ventral cochlear nucleus (AVCN)
3. Globular bushy cells which also receive a giant synapse
4. Contralateral medial nucleus of the trapezoid body (MNTB)
5. Sign inverting synapse so that an interneurone can provide inhibitory input to the lateral superior olive (LSO)

The same ISO cell receives excitatory input from the ipsilateral AVCN via a spherical bushy cell

Question 13

Interaural Intensity Difference

- Output

Answer 13

If contralateral intensity is higher than ipsilateral intensity then the LSO output is inhibitory and a weak output is created

Question 14

Duplex Theory of Sound Localisation in Azimuth

Answer 14

• Interaural time difference

- Interaural intensity difference