Chapter 10: Hearing II

Question 1

Describe the concept of interaural time difference and its importance.

Answer 1

Interaural time difference is the difference in time between a sound arriving at one ear versus the other. It is an important cue for localizing sound.

Question 2

How do the medial superior olive structures help in sound localization?

Answer 2

The medial superior olive structures serve as relay stations in the brain stem where inputs from both ears contribute to the detection of the interaural time difference, which in turn is critical for localizing sound.

Question 3

What is the interaural level difference?

Answer 3

The interaural level difference is the difference in level (intensity) between a sound arriving at one ear versus the other. It helps with the process of sound localization.

Question 4

What happens to sound information traveling to the ears after a single synapse in the cochlear nucleus?

Answer 4

The information from each ear travels to both the medial superior olive and the lateral superior olive on each side of the brain stem.

Question 5

Why is the cone of confusion confusing?

Answer 5

The cone of confusion is the region of positions in space where all sounds produce the same time and level (intensity) differences. In such a situation it is difficult to localize sound, which is confusing to the listener.

Question 6

Provide one reason why cones of confusion are not major practical problems for the auditory system.

Answer 6

One such reason is that time and intensity differences are not the only cues for hearing the location of sound sources. The shape of the pinna, for instance, also helps with sound localization. It “funnels” sound energy into the ear canal, and does this more efficiently for some sound frequencies than for others. In addition, the intensity of each frequency varies slightly according to the direction of the sound, and this variation provides the listener with another localization cue.

Question 7

What does the head-related transfer function describe?

Answer 7

This function describes how the pinna, ear canal, head, and torso change the intensity of sounds with different frequencies that arrive at each ear from various locations in space.

Question 8

How is the spectral composition of sounds a possible cue for auditory distance?

Answer 8

The spectral composition of sounds is a possible cue for auditory distance because the sound-absorbing qualities of air dampen high frequencies more than low frequencies, so when sound sources are far away, higher frequencies decrease in energy more than lower frequencies as the sound waves travel from the source to your ear. This variation between frequencies reaching the ear helps the listener to estimate the distance between him/her and the sound source.

Question 9

What does the inverse-square law state?

Answer 9

The inverse-square law states that as distance from a source increases, intensity decreases faster such that the decrease in intensity is the distance squared.

Question 10

How do the relative amounts of direct versus reverberant energy provide a cue for auditory distance?

Answer 10

The relative amounts of direct versus reverberant energy provide a cue for auditory distance because when a sound source is close to the listener, most of the energy reaching the ear is direct, whereas reverberant energy provides a greater proportion of the total when the sound source is farther away.

Question 11

What is a fundamental frequency?

Answer 11

A fundamental frequency is the lowest-frequency component of a complex periodic sound.

Question 12

Describe the phenomenon of the “missing fundamental.”

Answer 12

The “missing fundamental” is the phenomenon in which listeners will still hear the pitch of a missing fundamental frequency of a harmonic sound even if it is not present in the actual sound wave.

Question 13

What is timbre?

Answer 13

Timbre is the psychological sensation by which a listener can judge that two sounds that have the same loudness and pitch are dissimilar. Timbre quality is conveyed by harmonics and other high frequencies.

Question 14

What is the difference between the attack and the decay of a sound?

Answer 14

The attack of a sound is the part during which amplitude increases. The decay of a sound is the part during which the amplitude decreases.

Question 15

How does source segregation help us to distinguish various sounds in our environment?

Answer 15

Source segregation is the processing of an auditory scene consisting of multiple sound sources into separate sound images. This process helps us ultimately distinguish between the different sound sources in our environment.

Question 16

Describe the idea of auditory stream segregation.

Answer 16

Auditory stream segregation is the perceptual organization of a complex acoustic signal into separate auditory events for which each stream is heard as a separate event.

Question 17

What happens when a sequence of notes that have increasing and decreasing frequencies is presented and tones deviate from the rising/falling pattern?

Answer 17

These deviating tones are heard to “pop out” of the sequence because they do not share the same timbre as the rest of the notes in the group.

Question 18

How is “hearing through” an interruption consistent with the Gestalt principle of good continuation?

Answer 18

“Hearing through” an interruption is consistent with the Gestalt principle of good continuation because in this case, the listener is able to “make up” for the missing sound piece due to the interruption. The Gestalt principle of good continuation also states that the perceiver will make up for a lost piece by filling in for it.

Question 19

Explain the idea of restoration of complex sounds.

Answer 19

Restoration of complex sounds can occur when listening to speech or music, which are complex sounds. The missing notes or segments of speech are filled in by the listener, and the whole piece is thus restored.

Question 20

attack

Answer 20

The part of a sound during which amplitude increases (onset).

Question 21

auditory stream segregation

Answer 21

The perceptual organization of a complex acoustic signal into separate auditory events for which each stream is heard as a separate event.

Question 22

azimuth

Answer 22

The angle of a sound source on the horizontal plane relative to a point in the center of the head between the ears. Azimuth is measured in degrees, with 0 degrees being straight ahead. The angle increases clockwise toward the right, with 180 degrees being directly behind.

Question 23

cone of confusion

Answer 23

A region of positions in space where all sounds produce the same time and level (intensity) differences (ITDs and ILDs).

Question 24

decay

Answer 24

The part of a sound during which amplitude decreases (offset).

Question 25

directional transfer function (DTF)

Answer 25

A measure that describes how the pinna, ear canal, head, and torso change the intensity of sounds with different frequencies that arrive at each ear from different locations in space (azimuth and elevation).

Question 26

fundamental frequency

Answer 26

The lowest-frequency component of a complex periodic sound.

Question 27

interaural level difference (ILD)

Answer 27

The difference in level (intensity) between a sound arriving at one ear versus the other.

Question 28

interaural time difference (ITD)

Answer 28

The difference in time between a sound arriving at one ear versus the other.

Question 29

inverse-square law

Answer 29

A principle stating that as distance from a source increases, intensity initially decreases much faster than distance increases, such that the decrease in intensity is equal to the increase in distance squared. This general law also applies to optics and other forms of energy.

Question 30

lateral superior olive (LSO)

Answer 30

A relay station in the brain stem where inputs from both ears contribute to detection of the interaural level difference.

Question 31

medial superior olive (MSO)

Answer 31

A relay station in the brain stem where inputs from both ears contribute to detection of the interaural time difference.

Question 32

source segregation or auditory scene analysis

Answer 32

Processing an auditory scene consisting of multiple sound sources into separate sound images.

Question 33

timbre

Answer 33

The psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar. Timbre quality is conveyed by harmonics and other high frequencies.