Localistion & auditory scene analysis

Question 1

define sound localisation

Answer 1

ability to identify location of sound

Question 2

how do we localise sound? 2 cues

Answer 2

1. binaural cues: require comparison of signals in left and right ears and are vital for signalling location of a sound in azimuth
   - interaural time differences
   - interaural level differences
2. monaural cues> work with one ear can help localise the elevation and distance of a sound

Question 3

azimuth

Answer 3

left-right plane

Question 4

interaural time differences

Answer 4

difference in time at which a sound arrives at 2 ears depends on its location in azimuth
- if sound is straight ahead there is no difference in time but at the side the sound will reach the nearer ear first

Question 5

phase locking

Answer 5

mechanisms where auditory system keeps track of times of occurrence of sound fluctuations

Question 6

range of ITDs encountered depends on

Answer 6

• speed of sound

- distance between the 2 ears

Question 7

interaural level differences

Answer 7

• the relative sound pressure level reaching the 2 ears also depends on the location of the source in azimuth
• reduction in sound level for far ear is due to acoustic shadow created by head
• high frequency = large shadow,, low frequency = smaller shadow

Question 8

where does processing ITDs and ILDs take place in brain

Answer 8

superior olivary complex

• the lateral superior olive (LSO): contains neurons that are sensitive to ILDs
• the medial superior olive (MSO): contains neurons that are sensitive to ITDs

*needed to code info form both ears

Question 9

strengths and weaknesses off binaural cues

Answer 9

• ITDs and ILDs provide complementary info on azimuth location
• ILDs work well for low frequency sounds
• ILDs provide info about high frequency sounds
• however, they don’t tell us about other dimensions

Question 10

cone of confusion

Answer 10

= area of pace you can’t differentiate due to binaural cues

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

Question 11

monaural localisation cues - elevation

Answer 11

when sound reflects off the nooks and crannies of your external ear, the relative intensity of different frequencies sound waves changes

• this changes with sound source elevation
• individuals have different ear shapes and will filter the frequency content of complex sounds in lightly different way
• artificially altering ear shape with plastic moulds impairs the ability to localise sound elevation found people were impaired but overtime learnt

Question 12

monaural localisation cues - distance
relative intensity
reverberation

Answer 12

relative intensity
- sound intensity decreases with distance, so closer object will tend to have greater amplitudes than farther ones

reverberation
= the way in which sound reflects off objects also rpvodes a cue to distance
- brain can use reverberation to infer something about distance

direct energy = increased amplitude
reverbrent energy = delayed and decreased amplitude

Question 13

define precedence effect

Answer 13

only receive 1 sound source when there are multiple reverberations

Question 14

filter properties of the pinnae

Answer 14

provide info about elevation

Question 15

auditory scene analysis

Answer 15

= how we go about grouping objects

- needs to segregate other sound sources and group components from same source

Question 16

strategies for grouping and segregating

Answer 16

1. spectral grouping = combining different frequency sound components that occur at the same time
   - Harmonicity: if component is mistuned it will be heard
   - common frequency change: frequency components that change together tend to group together
2. sequential grouping = combining sequences of sound over time
   - Auditory stream segregation: organising sounds overt into separate preceptual events
   - similarity of pitch
   - temporal proximity (timing)
   - similarity of timbre (diff timbre = segregation)
   - continuity - when sounds stay constant