Chapter 12: Hearing in the Environment

Question 1

What is auditory space and what are the different coordinates within it?

Answer 1

Auditory space: the area that surrounds an observed; auditory space exists wherever there is sound.

Coordinates within auditory space:

• Azimuth coordinates: position left to right
• Elevation coordinates: position up and down
• Distance coordinates: position from the observer

Question 2

What are binaural cues and what are the different types?

Answer 2

Binaural cues are cues for sound localization which are based on the comparison of the signals received by the left and right ears.

Types of binaural cues:

• Interaural time difference
• Interaural level difference

Question 3

How does Interaural time difference work?

Answer 3

Interaural time difference is the difference between the times sounds reach the two ears.

This provides information about azimuth coordinates where, if the sound reaches both ears at the same time it is either directly behind or in front of the person but, if it reaches one ear before the other, it is either to the left or right (depending on which ear it reaches first). How far to the left/right is determined by the amount of delay.

Question 4

How does Interaural level difference work?

Answer 4

Interaural level difference is the difference in sound pressure level reaching the two ears. This cue works best for higher frequency sounds.

It provides information about sound location (azimuth coordinates) because the head casts an acoustic shadow, reducing the pressure level of sound waves that reach the farther ear.

Question 5

What is the cone of confusion?

Answer 5

The cone of confusion are ambiguous points in the auditory space. These are points that have the same ITD and ILD despite being in different locations so binaural cues don’t help localize it. The cone of confusion often refers to sounds with different elevations.

Question 6

What are monaural cues and how do they work?

Answer 6

Monaural cues are sound localization cues that only use one ear. monaural cues use differences in distribution and frequency to localize sound.

For example, the pinnae and head affect the intensities of frequencies.And elevation can be determined by how the sound waves hit the pinnae.

Question 7

What is the Jeffress Model of auditory localization?

Answer 7

Jeffress Model of auditory localization suggests that neurons are wired to recieve information from both ears and if sound from both ears reaches the neuron at the same time, the sound is directly in front or behind. Any discrepency represents a shift to the left or right.

The central neuron in this circuit is called the coincidence detector as it fires if the sound reaches the it at the same time. Other neurons in the circuit fire to locations corresponding to other ITDs.

Question 8

What is the first site of binaural integration in the auditory pathway?

Answer 8

The superior olivary nucleus.

Question 9

What is the role of area A1?

Answer 9

Area A1 is involved in locating sounds. In studies with ferrets, lesioning A1 reduced their ability to localize sound. Deactivating A1 with medication in cats led to poor ability to localize.

Question 10

What is the posterior belt area and what is it’s function?

Answer 10

The posterior belt area is the pathway from the parietal lobe to the frontal lobe. It is part of the “where pathway” of the auditory system. It is involved in more advanced and specific sound localizing than area A1.

Question 11

What is the anterior belt area and what is it’s function?

Answer 11

The anterior belt area is the pathway from the temporal lobe to the frontal lobe. It is part of the “what pathway” of the auditory system. It is responsible for identifying/differentiating between complex sounds.

Question 12

What are the dorsal and ventral streams in the auditory system?

Answer 12

The ventral stream is the WHAT stream. It starts in the anterior belt and goes to the temporal lobe and prefrontal cortex. It identifies sounds.

The Dorsal Stream is the WHERE stream. It starts in the posterior belt and extends to the parietal and prefrontal cortex. It locates sounds.

Question 13

What is the difference between direct and indirect sounds?

Answer 13

Direct sounds: sound that reaches the listener’s ears straight from the source

Indirect sounds: sound that is reflected off of environmental surfaces before reaching the listener’s ears.

When outside, usually sounds are direct, when inside they are usually indirect.

Question 14

Describe Litovsky et al.’s study on the precedence effect.

Answer 14

Participants sat between two speakers, one lead, one lag. If there was a delay between the lead and lag greater than 1/10 of a second, participants heard 2 sounds. If the delay was 5-20ms though they heard 1 sound and described it as coming from the lead speaker.

This is called the precedence effect where we perceive sound as coming from the source that reaches our ear first.

Question 15

What are characteristics of the precedence effect?

Answer 15

If there is too much of a lag, the delayed sound is perceived as an echo

even when fused together, too many sources for one sound degrade the quality of the sound.

Question 16

What is an auditory scene? Auditory scene analysis?

Answer 16

It is the array of all sound sources in an environment.

Auditory scene analysis is the process by which sound sources in the auditory scene are separated into individual perceptions. Because the cochlea processes simultaneous sounds together, auditory scene analysis must be a top down process.

Question 17

What are heuristics that help to perceptually organize sound stimuli occurring simultanously?

Answer 17

Onset time: sounds that start at different times are likely to come from difference source

Location: single sound sources tend to come from one location and to move continuously

Similarity of timbre and pitch: similar sounds are grouped together.

Question 18

What heuristics help to perceptually organize sound stimuli occurring in a sequence?

Answer 18

Similarity of pitch: sounds that share a similar pitch overtime are perceived as the same source

Auditory stream segregation: the perception of a string of sounds as belonging together

Auditory continuity: sounds that stay constant or change smoothly are produced by the same source.

Experience teaches us how to group sounds.
Melody schema: a representation of a familiar melody stored in our memory.

Question 19

What is the experiment by Bregman and Campbell?

Answer 19

They played a stimuli at various speeds alternating between high and low tones.

When the stimuli were played slowly, the perception is hearing high and low tones alternating. When the stimuli were played faster, the perception is hearing two streams of sound, one high and one low. `

Question 20

What is the experiment by Warren et al.?

Answer 20

Tones were presented interrupted by gaps of silence or by noise.
In the silence condition, listeners perceived the sound as stopped during the gaps.
In the noise condition, listeners perceived the sound as continuing behind the noise.

Question 21

What is the visual capture?

Answer 21

Also called the ventriloquist effect. It is when an observer perceives the sound as coming from the visual location rather than the source of the sound. For example, in an experiment by Sekuler et al. balls moving without sound appeared to move past each other but balls moving with an added click sound appeared to collide.