Auditory spatial processing

What is retinitis pigmentosa

partial vision

What is allocentric representations of sound

where is the sound in relation to other sounds

What is egocentric representations of sound

Where is the sound in relation to me

Why might internal representations be inaccurate

limited information

spatial biases

conflicting cues

hard to track multiple moving objects

what are azimuth cues

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

where are the ITD and ILD located

ITD: medial superior olive (MSO)

ILD: lateral superior olive (LSO)

How long does it take for ITTD cues to travel across the head

approx 0.6ms

what frequency are ILDs better for

High frequency sounds because low frequency sounds are not substantially attenuated by the head

how can you measure the smallest values for discriminating ITD and ILD

headphones

what is discrimination

involves more than one sound e.g. minimum audible angle (MAA), the smallest detectable difference between the azimuth of 2 source sounds

what are the ITD and ILD discrimination thresholds

For sinewaves, a change in ITD of 10 microseconds is detectable at 900 Hz

ITDs cannot be detected about 1500 Hz

ILDs thresholds are the smallest for frontal sounds, where ILDs of approximately 1-2 dB are detectable

What is duplex theory

the perceived azimuth of low-frequency sounds is dominated by ITD

For high-frequency stimuli the auditory system weights the ILD more when determining the azimuth

ITD for low frequencies, ILD for high frequencies

Sound localisation is poorest where neither ITD and ILD cues work well

What are the 2 auditory distance cues

1. auditory level

2. reverberation

What is auditory level

lower level sounds are perceived as further away

sound level falls by 6 dB for each doubling of the source distance

what is reverberation

reverberant sounds are judged as more distant

dependent on absorption by the surrounding walls, floor and ceiling

what is systematic bias

an increase in underestimation as distance increases

unless the sound is fairly close, we are not particularly good at judging distance

what is the precedence effect

When two identical versions of a sound are heard, with a brief delay between them, a single sound is heard. the spatial position is determined by the first sound

how does the precedence effect work

when listening in a room, sound arrives at the ear direct from the source or reverberant

despite the reflections we perceive only a single source and can locate the sound accurately

what is echo suppression

two sounds are heard as one sound if the interval between them is brief

what does the precedence effect depend on

depends on sound level - if the sound is greater than 10-15 dB than the first, then the precedence effect no longer applies and 2 sounds are heard

stimulus dependent - the precedence effect does not apply to ongoing tones

how do hearing aids alter auditory spatial cues

automatic gain control disrupts level cues for distance

automatic gain control and directional microphones alter the direct-to-reverberant sound energy ration

independent automatic gain control at two ears may disrupt binaural localisation cues especially when the head is moved

why do hearing aids disrupt the perception of externalised sounds

loss of pinna cues