localisation

Question 1

Azimuth

Answer 1

Around you from 0 to 180 and then negative
Left and right, front and back also used

Question 2

Elevation

Answer 2

Plus 90 to negative 90

Question 3

Externalisation

Answer 3

Things are internalised in the head when using headphones

Question 4

Binaural cues

Answer 4

Two ears working together

Question 5

Interaural level differences

Answer 5

Head is an obstacle to sound, so when sound comes in from the side one ear is in an acoustic shadow
Interaural level difference is the difference in sound levels that our different ears get

Question 6

Interaural differences get larger with increasing frequency

Answer 6

Higher in frequency the less diffraction

Question 7

Interaural time delay - Klumpp (1956)

Answer 7

Sound takes up to 700 micro seconds to travel the extra few centimetres
The smallest detectable difference is 10 micro seconds

Question 8

Model of sound lateralisation - Jeffress (1948)

Answer 8

Medial superior olive
Exploits axonal transmission delays
Only fire if they are close in time frame
Coincidence detector tells them where they converge
The wiggly diagram with explosions

Question 9

Mammalian auditory systems

Answer 9

Use a population code that tells us if its on the left or the right with two channels tuned in those directions

Question 10

The Endbulb of Held

Answer 10

Communication of precise phase-locked action potentials to the central nervous system requires extraordinary synapses in the brainstem
So big (and ugly) because it tries to produce very precise timing to the output

Question 11

Pure tones and localisation

Answer 11

Mid frequency pure tones hard to localise because the interaural differences are hard to localise and interaural time delay is ambiguous
But it is rare to happen with natural sounds!

Question 12

Pinna cues

Answer 12

ILD and ITD are the same at all points on conical surface
Sound reflects from corrugations of the pinna and interferes with the sound directly entering the meatus
Interference changes the sound spectrum producing a direction dependent colouration
Important for showing where things are away from the mid area - Cardiff studies

Question 13

Pinnae shape

Answer 13

Everyone has slightly different pinnae and that affects how we hear things, particularly as we grow and change

Question 14

Pinnae shape - Gardner & Gardner (1973)

Answer 14

Lots of errors when pinnae filled with rubber
Less errors when cavities left open

Question 15

Head movements to discriminate front and back

Answer 15

Turning our head turns it into a binaural problem
Can tell using interaural time delay to see which ear leads

Question 16

Effects of room reverberation

Answer 16

Auditory system survives acoustic rays better than our visual system
Auditory system can listen to first sound and ignore reverb, no matter the loudness or distance
Known as precedence effect or law of first wavefront

Question 17

Precedence effect - Wallach (1949)

Answer 17

One loudspeaker adjusted in various ways (distance, intensity, delay)
Sound is heard to come from the speaker whose signal arrives earliest at the listener
Auditory system ignores location of echoes occurring milliseconds after the direct sound

Question 18

Externalisation and distance (how to make sound in headphones sound like its coming from outside)

Answer 18

Realistic individual pinnae cues (Measure the ears)
Reverberation (Different to each ear)
Source stability during head turn (Gives sense of sound staying outside of your head space)