Auditory Perception II: Space Perception

Question 1

How do we use two ears to infer information about depth and distance

Answer 1

differences in the arrival of sound at the two ears allow us to use the ONSET of a sound to localize

– time difference in onset of sound allows us to infer direction (arrives first in left, must come from left)

Question 2

What are the difference sources of spatial information in auditory perception?

Answer 2

ITD
IPD
ILD

Question 3

Interaural Time Difference (ITD)

Answer 3

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

• • amount of time delay gives us info about location
• • more useful at low frequencies, not good at high frequencies

Question 4

Azimuth

Answer 4

An imaginary circle that extends around us, in a horizontal plane; allows us to measure direction of sound (organized by degrees)

Question 5

What location in space would give us 0 ITD

Answer 5

right in front, right behind us

• • equal distance from both ears
• • 0 degrees, 180 degrees

Question 6

What location in space would give us maximum ITD

Answer 6

directly on one side (right or left)

• • longest path to travel from one ear to the other
• • 90 degrees, -90 degrees

Question 7

What units are used to describe ITD?

Answer 7

microseconds (1000th of 1 millisecond)

– extremely small time differences

Question 8

Interaural Phase Difference (IPD)

Answer 8

Differences in the PHASE of soundwaves arriving at the two ears can be used for localization

Question 9

What is the maximum time difference from one ear to another?

Answer 9

about 0.6 milliseconds

Question 10

Interaural level difference (ILD)

Answer 10

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

• • sounds are more intense at the ear closer to sound source
• • generally correlates with angle of sound source (like ITD), but correlation is not quite as great as it is with ITDs

Question 11

Where is ILD highest?

Answer 11

90 degrees and –90 degrees

Question 12

Where is ILD lowest?

Answer 12

0 degrees and 180 degrees

Question 13

_____ and _____ differences play a complementary role

Answer 13

PHASE and INTENSITY

Question 14

How do phase and intensity differences complement each other?

Answer 14

1) Phase differences work for low frequency sounds.
2) Intensity differences work for high frequency sounds.
3) The combination allows us to localize most sounds.

Question 15

Phase differences work best for ____ frequency sounds

Answer 15

low frequency

Question 16

Intensity differences work best for ___ frequency sounds

Answer 16

high frequency

Question 17

Cone of Confusion

Answer 17

The limitation to time and intensity differences for finding location

There are symmetries that give the same ITD and ILD cues for both ears (up/down and front/behind)

Question 18

How do we deal with the Cone of Confusion?

Answer 18

• head movements (tilting head)

- shape of the pinnae, primarily for high- frequency sounds

Question 19

How do the pinnae in the outer ear help with resolving ambiguities in sound location

Answer 19

pinnae funnel certain sound frequencies better than others, and the intensity of each frequency varies depending on the direction of the sound

Question 20

What is the simplest cue for listeners to judge distance of sounds?

Answer 20

Relative intensity of sound

Question 21

Inverse-square law

Answer 21

As distance from a source increases, intensity decreases faster such that decrease in intensity is distance squared

*our brain knows and uses this to estimate distance based on intensity

Question 22

Spectral composition of sounds

Answer 22

Higher frequencies decrease in energy more than lower frequencies as sound waves travel from source to one ear

• the further something is, the less high frequency content we have
• if a sound has a lot of high frequency content, it is probably closer by

Question 23

Direct vs. reverberant energy

Answer 23

Direct: sound directly coming from the source
Indirect/reverberant: sound coming from bouncing off environment

• the closer you are, the greater ratio of direct sound you have
• the brain judges the ratio of direct to reverberant in order to determine how close or far something is

Question 24

Inverse accoustics

Answer 24

our brain inverts the laws of physics for sound in order to perceive them accurately

Question 25

What happens when you remove the first harmonic/fundamental frequency?

Answer 25

the brain fills it in somehow, and we still perceive the same pitch

Question 26

Missing-fundamental effect

Answer 26

when you remove the first harmonic/fundamental frequency, the brain fills it in somehow and we still perceive the same pitch --brain may be looking at the peaks, which corresponds to the fundamental harmonic

Question 27

Timbre

Answer 27

quality of sound; psychological sensation by which a listener can judge that two sounds that have the same loudness and pitch are dissimilar - -> conveyed by harmonics - -> influenced by ONSET (attack)

Question 28

Cocktail party problem

Answer 28

How does auditory system sort out multiple sound sources occurring simultaneously? AKA source segregation or auditory scene analysis

Question 29

What are the strategies for sound source segregation?

Answer 29

``` – Spatial separation between sounds – Grouping on basis of sounds’ spectral or temporal qualities – Auditory stream segregation – Grouping by frequency – Grouping by timbre – Grouping by onset ```

Question 30

Auditory stream segregation

Answer 30

strategy for sound source segregation; the perceptual organization of a complex acoustic signals into separate auditory events for which each stream is heard as a separate event

Question 31

Grouping by onset

Answer 31

sounds that start together/end together tend to get grouped together note: similar to gestalt law of common fate

Question 32

Filling in/Restoration

Answer 32

brain fills in missing sounds so that they are continuous | ** interpolation, described as principle of continuity in gestalt