localisation and auditory scene analysis

Question 1

where is the visual information for the relative location of objects ?

Answer 1

Within the retinal image

Question 2

What does our ability to ascribe a spatial position rely on?

Answer 2

binaural and monaural cues

Question 3

What are binaural cues?

Answer 3

Require comparison of signals in left and right ears

Question 4

Why are binaural cues important?

Answer 4

Vital for signalling location of a sound in azimuth (left right plane)

Question 5

What is monaural cues?

Answer 5

Work with one ear to localise the elevation (up down) and distance of a sound

Question 6

What does monaural cues do with the pinna?

Answer 6

It filter properties of pinna

Works with intensity and reverbration

Question 7

What is an ITD?

Answer 7

This is where the relative time at which a sound arrives at the two ears depends on its location in azimuth

Question 8

What happens if the sound source is straight ahead? - ITD

Answer 8

The distance to each ear is the same and there is no difference in time

Question 9

What if the source is positioned to one side? - ITD

Answer 9

The sound will reach the nearer ear first

Question 10

What does the range of ITDS depend on?

Answer 10

Speed of sound (330ms through air)
Distance between two ears (larger heads create bigger ITD range)

Question 11

What is the maximum ITD in humans?

Answer 11

600 (0.6ms)

Question 12

When is ITD most useful?

Answer 12

Low frequency or abrupt onset sounds

Question 13

What is interaural level differences (ILD)

Answer 13

The relative sound pressure level reaching the two ears depends of location of source in azimuth

Question 14

How does a reduction in sound level occur?

Answer 14

Due to the acoustic shadow created by the head for high frequency sounds

Question 15

Where does processing of ITD and ILD start?

Answer 15

Within the brainstem in superior olivary complex

Question 16

Where are the neuron’s sensitive to the ILDS found?

Answer 16

LSO

Question 17

Where are the neurons sensitive to ITDS found?

Answer 17

MSO

Question 18

Whats the strengths of binaural cues?

Answer 18

ITDS and ILDS provide complementary information about azimuth location

ITDS good for low freq sounds

ILDS good for high freq sounds

Question 19

What are the limitations of binaural cues?

Answer 19

Ambiguous information about elevation and nothing about distance
Cone of confusion : Set of points from which a sound source will produce identical ITDS and ILDS

Question 20

What happens when sound reflects of the external ear?

Answer 20

Intensity of relative frequencies sound waves changes which changes the sound source elevation

Question 21

How do individuals filter the frequency content ?

Answer 21

Through having the different ear shapes

Question 22

How does relative intensity link to monaural localisation cues such as distance?

Answer 22

Sound intensity decreases with distance so closer objects will tend to have greater amplitudes than farther ones

Question 23

What impairs the ability to localise sound elevation?

Answer 23

Artificially altering ear shape with plastic moulds

Question 24

How does reverberation link to monaural localisation cues?

Answer 24

The way in which sound reflects off objects provides a cue to distance

Multiple reflections combine to produce a persistance of sound called reverberation

The distance of a source alters the relative intensity and timing of direct and reverberant sounds

Question 25

What is the precedence effect?

Answer 25

This is where similar sounds arrive in quick succession from different locations that are localised according to the direction of the first sound

Question 26

What is auditory scene analysis?

Answer 26

This is where the auditory system needs to segregate the components of sound that come from different sound sources by grouping the components of the sound that come from the same sound source

Question 27

What principles does grouping in auditory system follow?

Answer 27

Common fate, proximity, similarity and continuity

Question 28

What is spectral grouping?

Answer 28

Combining different frequency sound components that occur at the same time

Question 29

What is sequential grouping?

Answer 29

Combining sequences of sounds over time

Question 29

How does common frequency change link to spectral grouping?

Answer 29

Analogous to principle of common fate
Frequency components that change together tend to group together

Question 29

How does harmonicity link to spectral grouping?

Answer 29

If a component is mistuned to other components it will be heard as a separate sound

Question 29

What is auditory stream segregation?

Answer 29

The process of organising sounds over time in separate perceptual events

Question 30

Similarity of pitch and sequential grouping?

Answer 30

Sounds with similar pitch are produced by same source
Increasing frequency difference promotes stream segregation

Question 30

What happens if we change the characteristics of sounds?

Answer 30

Either group the sequence or segregate into multiple streams

Question 31

Temporal proximity and sequential grouping?

Answer 31

Sounds that occur in rapid progression tend to be produced by same source
Increasing presentation rate also promotes stream segregation

Question 32

Similiarity of timbre and sequential grouping?

Answer 32

Sound sources have distinct timbre providing a good cue for segregation

Question 33

Continuity and sequential grouping?

Answer 33

Sounds that stay constant or change smoothly are produced by same source

Perceived as continuous even when interrupted by noise

Question 34

What is phonemic restoration?

Answer 34

Effect not restricted to tones