auditory spatial processing (copy)

egocentric representation

where is the sound in relation to me

allocentric representation

where is the sound in relation to other sounds

why may internal representations be inaccurate?

• limited information

• spatial biases

• conflicting cues

locking objects using sound

locating sound sources is not limited to frontal space as we have two ears

vision is limited to frontal space

binaural

listening with two ears

localisation

judging sound source location on terms of left-right direction, distance or elevation

azimuth cues

Interaural time difference (ITD) differences and interaural level differences (ILD) are primary cues for locating sounds.

inter-aural level difference cues

low frequency sounds are not attended to

ILD cues are better for localising high frequency sounds

intramural time difference cues

for azimuth localisation

takes .6ms for sound to travel across the head

duplex theory

the perceived azimuth of low frequency sounds is dominated by ITD

for high frequency stimuli- ILD is weighed more when determining azimuth

discriminating ITD and ILD thresholds

using headphones

ILD discriminations are smallest for..

frontal sounds

auditory level cue

lower level sounds are perceived as further away

reverberation cue

sounds that bounce of walls and ceilings before reaching ears- they are judged as more distant

critique of reverberant

dependant on the evnironement we are in, e.g. field vs small room

in a field the ground absorbs echos so there is no echo

judging distance systematic bias

an increase in underestimation as distance from sound increases

auditory elevation cues

the Pina (outer ear) have convolutions which shape the sound we hear, resulting in direction- dependant shaping

head related transfer function

the shaped frequency from spatial location- spectrum of white noise measured at the eardrum

dealing with ambiguity

moving head round helps us

HRTF

virtualisation techniques

where sounds are heard using headphones

headphones remove pinna cues- making the sound interlaised

HRTF can make the sounds externalised again

free-field presentation

where sounds are heard from speakers are different locations around the room

the precedence effect

so when two identical versions of sound are heard with a brief delay- a single sound is heard

spatial position is determined by the first sound

first sound dominates perception

echo suppression

two sounds are heard as one sound

the precedence effect depends on

• sound level (e.g. if sound is greater than the other)

• stimulus dependant (doesn’t apply to ongoing tones)

biases- looming sounds

sounds which are coming towards us

we have a preference for if it is rising in intensity and coming towards it

e..g. hearing a bus - allows us time to prepare

biases- threatening stimuli

e.g. rattlesnakes rattling- strong decrease in perceveived distance so we think its closer than it is

reverberation cues

echoes from walls

room size judgements are

underestmiated

reverberant rooms tend to be judged as later than anechoic rooms

anechoic

level cues only

reverberant

level and reverberant cues

hearing impairment

difficulty using ITD and ILD cues