29. localization

Question 1

Azimuth def?

Answer 1

• the location of a sound source in the HORIZONTAL plane

(side to side)

Question 2

Elevation def?

Answer 2

• the location of a sound source in the MEDIAN (VERTICAL) plane

(up and down)

Question 3

Distance def?

Answer 3

• how far a sound source is from the center of the head in any direction

Question 4

Minimum audible angle def?

Answer 4

The minimum angular separation between a reference sound source and a different sound source (emitting a tone of the same frequency)

that yields 75% correct judgments about the relative horizontal positions of the two sources.

Question 5

What 2 cues / pieces of information are there to perceive azimuth?

Answer 5

1. Interaural LEVEL differences
2. Interaural TIME differences

Question 6

Interaural Level Differences:
- what does “level” mean?

Answer 6

• intensity, “loudness,” amplitude

Question 7

Interaural Level Difference (ILD) def?

Answer 7

• Sound will have a lower volume at the ear that is farther from the sound source

Book def:
- Difference in sound intensity of the same sound at the two ears

Question 8

Interaural Level Differences:
- what are the 2 things that contribute? Which one is super more important than the other?

Answer 8

1. distance from sound makes sound quieter
   –> head only inc. distance max 14 cm
   –> only relevant with sounds very close to your head
2. acoustic shadow

Question 9

Acoustic shadow def?

Answer 9

• head creates a “shadow” that partially blocks sound waves. This reduces the loudness of the sound on the opposite side of the head from the sound source

book def:
- An area on the other side of the head from a sound source in which the loudness of the sound is reduced because the sound waves are partially blocked by the head

Question 10

Acoustic shadow more strongly affects high or low frequency sounds?

Answer 10

• HIGH frequency sounds!
• low frqs aren’t affected very much

Question 11

Acoustic shadow:
what locations /degrees are…
- max?
- min/none?

Answer 11

Where 0º = straight forward…

Max: 90º, 270º (ie L / R)
Min/none: 0º, 180º (ie front / back)

Question 12

Interaural time difference def?

Answer 12

The difference in arrival time of the same sound at the two ears

Question 13

Interaural time difference:
does it work better for high or low frqs? Or all frqs equally?

Answer 13

• all frqs equally!

Question 14

Interaural time difference:
Approx time diff. for 90º and 45º?

Answer 14

45º ≈ 300 microseconds
90º ≈ 600 microseconds

Question 15

Neural basis of localization:
What brain structure does it happen in?

Answer 15

• the medial superior olive (MSO)
• both L&R MSOs receive signals from both L&R ears

Question 16

Neural basis of localization:
- how does it work?
- What is it similar to in visual system?

Answer 16

• Neurons are tuned to diff. magnitudes of ITD
• they have time-delays in how fast signals from cochlear nucleus reach the neurons in MSO
• works similar to the mechanism for detecting motion in the visual system (with neuron 1 having a delay to get to neuron M)

Question 17

Why are echoes often not noticeable? What “effect” does this relate to?

Answer 17

• direct sound source creates shortest path to you
• we localize sounds based on where they first arrive from
• relates to precedence effect

Question 18

Precedence effect def?

Answer 18

localization is dominated by the sound that arrives first

Question 19

Cone of confusion def?

Answer 19

• A hypothetical cone-shaped surface in auditory space with axis in auditory canals
• when two equally distant sound sources are located on the surface of a cone of confusion…
• they have highly similar ILD and ITD.

so, their locations are confusable

Question 20

How do disambiguate ambiguous sounds?
(such as on a cone of confusion)

Answer 20

• move your head!
• moving your head changes the ILD and ITD

Question 21

What is the cue used to determine elevation?

Answer 21

Spectral shape cue

Question 22

Spectral shape cue def?

Answer 22

• shape of pinna changes amplification of sounds (depending on frq) based on their elevation
• we use this to judge elevation of a sound

Book def:
- pinna-induced modification in a sound’s frequency spectrum; amplifies and attenuates sounds of different frequencies at different elevations

Question 23

Describe the important study about elevation? What was the main result?

Answer 23

• they mapped the spectral shape cue for a person’s pinna, then changed it by altering the shape of their pinna with inserts
• this completely ruined their ability to judge elevation

Question 24

What effect would headphones have on localization? (without playing music)

Answer 24

• azimuth is fine
  –> ITD is equal
  –> ILD is muffled, but equal
• elevation info is really limited
  –> blocks the shape of the pinna

Question 25

Visual capture / ventriloquism effect def?

Answer 25

• Visually apparent location of sound determines perceived location from which a sound originates
• when there’s conflicting visual & auditory into, visual system overrules auditory

Question 26

Visual capture (affecting localization) is dependent on what 3 factors?

Answer 26

Visual and auditory events must be…
1. reasonably close in time
2. plausibly linked
3. plausibly close in space
–> earbuds & computer is good
–> comp. & speaker 2 rooms away is not