Localization

Question 1

How does the auditory system localize?

Answer 1

Horizontal plane:

• ITDs
• ILDs

Vertical plane

• Pinna cues
• Neuroplasticity

Question 2

What results in ITDs?

Answer 2

Physical path differences

Question 3

What results in ILDs?

Answer 3

Head shadow effect

Question 4

Why are ILDs negligible below 1500 Hz?

Answer 4

• Low frequencies are not attenuated much by the human head, as explained by the head shadow effect

Question 5

What are the 2 functions of the pinna?

Answer 5

• Collect and amplify sounds

- Localize sounds

Question 6

How does the pinna collect/localize sound?

Answer 6

• Its unique shape and different cavities produce peaks and notches that help inform a sound’s location in space
• There are groups of neurons sensitive to these notches
• The head and pinna form a direction-dependent filter
• These spectral cues help the auditory system discriminate between front and rear sound sources (Byrne & Noble, 1998)

Question 7

What higher auditory structures are involved with localization?

Answer 7

• Cochlear nucleus
• Superior olivary complex
• Inferior colliculus
• Auditory cortex

Question 8

How does the cochlear nucleus localize sound?

Answer 8

• Receives both monaural and binaural inputs
• Monaural inputs provide spectral notches that contribute to vertical localization
• Binaural inputs provide ITDs and ILDs

Question 9

How does the superior olivary complex localize sound?

Answer 9

• It is the most caudal structure to receive binaural inputs
• The medial superior olivary complex encodes ITDs
• The lateral superior olivary complex encodes ILDs

Question 10

How does the inferior colliculus localize sound?

Answer 10

• Sensitive to both ILDs and ITDs

Question 11

How does the auditory cortex localize sound?

Answer 11

• There are no topographic maps in the cortex

- Multimodal neurons help process a sound’s location in space

Question 12

How does the squelch effect improve localization with 2 ears?

Answer 12

• Improvement in internal SNR due to interaural comparisons

Question 13

What is the precedence effect?

Answer 13

Describes how the auditory system localizes sound in the presence of reflections

Question 14

What is localization dominance?

Answer 14

• Occurs when the perception of a sound’s location is dictated by the spatial cues and ITDs of the leading sound perceived by the ears, regardless of the perception of the lagging sound

Question 15

What is fusion?

Answer 15

Fusion results in the perception of a single sound

This occurs when the lead-lag delay is less than the echo threshold.

Question 16

What are the benefits/limitations of hearing aids in terms of localization?

Answer 16

Benefits:

• Providing audibility
• Preserving ILDs

Limitations:
- Cannot fix a distorted signal

Question 17

What are the benefits/limitations of cochlear implants in terms of localization?

Answer 17

Benefits:
- Preserve ILDs

Limitations:
- Cannot encode ITDs because of electrode array design

Question 18

What are different strategies that can improve localization with hearing aids and cochlear implants?

Answer 18

• Binaural or bimodal fitting
• Increase bandwidth to provide a wider frequency response
• Program w/ slow acting compression
• Implement wireless technology that allows for inter-ear compression
• Aural rehab. suggests that localization can be relearned