Perception - Localisation and Auditory Scene Analysis Flashcards
What is the difference between localisation information in vision and audition?
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
What are two types of cues used for localising sounds?
Binaural
Monaural
What are binaural cues?
Require comparison of signals in left and right ears
What location do binaural cues help to localise?
Azimuth (left-right plane)
What are the two types of binaural cues?
Interaural time differences (ITDs)
Interaural level differences (ILDs)
What are ITDs?
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)
What is the maximum ITD in humans?
~600μs
What sounds are ITDs useful for?
Low frequency or abrupt-onset
What are ILDs?
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
What sounds are ILDs most useful for?
High frequency
What is the physiology of binaural cues?
Because required to compare between ears, can’t happen in ears
Processing starts within brainstem in superior olivary complex (superior olive)
What is the superior olive?
Where binaural cues start to be calculated
What are the two types of neuron in the superior olive?
Lateral SO
Medial SO
What binaural cue are the neurons in the lateral SO sensitive to?
ILDs
What binaural cue are the neurons in the medial SO sensitive to?
ITDs
What are the strengths of binaural cues?
Provide complementary information about azimuth location
ITDs work well for low frequency sounds
ILDs provide information about high frequency sounds
What are the weaknesses of binaural cues?
Don’t tell us about elevation or distance
Ambiguous whether sound front or behind
Range of locations that could produce ILDs and ITDs
What is the cone of confusion?
Set of points from which a sound source will produce identical ITDs and ILDs
What are monaural cues?
Work with one ear
What location do monaural cues help to localise?
Elevation (up-down plane)
Distance of sound
What is a monaural cue for working out elevation?
Filter properties of the pinnae
How do the filter properties of the pinnae help localise elevation?
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
What does artificially altering ear shape with plastic moulds do?
Impairs ability to localise sound elevation - although brain does adapt
What are two types of monaural cues for localising distance?
Relative intensity
Reverberation
