Perception - Localisation and Auditory Scene Analysis

Question 1

What is the difference between localisation information in vision and audition?

Answer 1

Visual information for relative location of objects contained within retinal image - in the input

Place activated by sound on cochlea doesn’t indicate location - auditory input has no spatial information

Question 2

What are two types of cues used for localising sounds?

Answer 2

Binaural

Monaural

Question 3

What are binaural cues?

Answer 3

Require comparison of signals in left and right ears

Question 4

What location do binaural cues help to localise?

Answer 4

Azimuth (left-right plane)

Question 5

What are the two types of binaural cues?

Answer 5

Interaural time differences (ITDs)

Interaural level differences (ILDs)

Question 6

What are ITDs?

Answer 6

If sound on one side, will arrive at one ear faster than the other

Relative time at which sound arrives at two ear depends on is location in azimuth

Requires precise signalling of timing (phase-locking)

Question 7

What is the maximum ITD in humans?

Answer 7

~600μs

Question 8

What sounds are ITDs useful for?

Answer 8

Low frequency or abrupt-onset

Question 9

What are ILDs?

Answer 9

Relative intensity/amplitude depends on location

Relative sound pressure level reaching two ears depends on location of source in azimuth

Reduction in sound level occurs for far ear, due to acoustic shadow created by head

Question 10

What sounds are ILDs most useful for?

Answer 10

High frequency

Question 11

What is the physiology of binaural cues?

Answer 11

Because required to compare between ears, can’t happen in ears

Processing starts within brainstem in superior olivary complex (superior olive)

Question 12

What is the superior olive?

Answer 12

Where binaural cues start to be calculated

Question 13

What are the two types of neuron in the superior olive?

Answer 13

Lateral SO

Medial SO

Question 14

What binaural cue are the neurons in the lateral SO sensitive to?

Answer 14

ILDs

Question 15

What binaural cue are the neurons in the medial SO sensitive to?

Answer 15

ITDs

Question 16

What are the strengths of binaural cues?

Answer 16

Provide complementary information about azimuth location

ITDs work well for low frequency sounds

ILDs provide information about high frequency sounds

Question 17

What are the weaknesses of binaural cues?

Answer 17

Don’t tell us about elevation or distance

Ambiguous whether sound front or behind

Range of locations that could produce ILDs and ITDs

Question 18

What is the cone of confusion?

Answer 18

Set of points from which a sound source will produce identical ITDs and ILDs

Question 19

What are monaural cues?

Answer 19

Work with one ear

Question 20

What location do monaural cues help to localise?

Answer 20

Elevation (up-down plane)

Distance of sound

Question 21

What is a monaural cue for working out elevation?

Answer 21

Filter properties of the pinnae

Question 22

How do the filter properties of the pinnae help localise elevation?

Answer 22

When sound reflects off the nocks and crannies of external ear, relative intensity of different frequencies sound waves changes with sound source elevation (and azimuth - front or back)

Individuals have different ear shapes and will filter frequency content of complex sounds in slightly different way

Question 23

What does artificially altering ear shape with plastic moulds do?

Answer 23

Impairs ability to localise sound elevation - although brain does adapt

Question 24

What are two types of monaural cues for localising distance?

Answer 24

Relative intensity

Reverberation

Question 25

How does relative intensity help to localise distance?

Answer 25

Sound intensity decreases with distance

Closer objects tend to have greater amplitude than farther ones

Question 26

How does reverberation help to localise distance?

Answer 26

Way sound reflects off objects provides a cue to distance

Multiple reflections combine to produce a persistence of sound called reverberation

Distance of source alters relative intensity and timing of direct and reverberant sounds