Spatial Hearing

Spatial hearing and sound localization mechanisms in the brain Henri Pöntynen February 9, 2016

Outline •  Auditory periphery: from acoustics to neural signals - Basilar membrane - Organ of Corti •

Spatial cues and neural processing - ILD - ID - !onaural cues

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"eferences

Auditory periphery

Auditory periphery: organs of hearing

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Outer ear: protection# amplification# locali$ation cues

!iddle ear: amplification %impedance matching&# protection

Inner ear: transduction of acoustic energy into neural signals

Cochlear anatomy ●

Coiled structure 'ith three li(uid filled chambers

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ransduction by the basilar membrane and the organ of Corti

Basilar membrane ●

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Sound pressure )ariations coupled to the inner ear )ia the tympanic membrane and the ossicular chain he mechanical properties of the basilar membrane )ary along its length * +ide and fle,ible ape, * Stiff and narro' base

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"esonance position depends on stimulus fre(uency * onotopy Comple, stimuli decomposed into fre(uency bands by mechanical fre(uency analysis

Cochlear transduction in the Organ of Corti

Localization cues

Localization cues ●

Direction-dependent features in acoustic signals

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.ori$ontal locali$ation )ia binaural cues * Signal sampled at / spatial locations# i0e0# at the / ears * Interaural le)el difference %ILD& * Interaural time difference %ID&

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1le)ation )ia monaural cues * Spectral features of the sound pressure signal at the eardrum

Brain circuit for spatial cues

Binaural cues: ITD ●

Difference in signal arri)al times at the t'o ears is determined by hori$ontal coordinate of the source0

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Delays 2 3ms

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1ffecti)e at lo' fre(uncies

edial superior oli!e "SO#

Coincidence detector model of SO ●

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ID processed in the !SO by coincidence detection principle uned detector neurons sho' highest acti)ity 'hen left4right signals are present simultaneously0  A,on length compensates for ID to align the signals at some detector neuron IDs represented as acti)ation of corresponding coincidence detectors0

Binaural cues: ILD ●

Diffraction 'hen 'a)elength 5 dimensions of the head * Sound 'a)es are unaffected by the acoustic obstacle presented by the head * Sound pressure le)el is the same at both ears0

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 At high fre(uencies# the head forms an acoustic shado' * Lo'er sound pressure le)el at the contralateral ear  * he degree of shado'ing depends on the hori$ontal coordinate of the source * !a,imum ILD at 6789# minimum ILD at 89  3;89

Lateral superior oli!e "LSO#

$eural processing of ILD ●

LSO in the superior oli)e

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!<B = medial nucleus of the trape$oidal body

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I1 neurons in the LSO perform binaural substraction to estimate the le)el difference0 * 1,citatory input from ipsilateral cochelea# * Inhibitory input from contralateral cochlea * Spi>e rate of LSOs in both hemispheres determined by ILD

onaural cues ●

Spectral features formed by constructi)e and destructi)e interference of direct sound and delayed reflections * Shoulder reflections * "eflections 'ithin pinna ca)ities

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 All source locations produce a uni(ue reflection pattern * .ead-related transfer function %."?& * @ni(ue to each subect

onaural cues

$eural processing of monaural cues ●

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 A3:
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ype I output proected to type O neurons in the IC  A/:
Summary

Summary ●

Stimuli di)ided into fre(uency bands by the basilar membrane

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Lo'-le)el locali$ation mechanisms in the midbrain

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.ori$ontal coordinate resol)ed mainly 'ith binaural cues * interaural time difference at lo' fre(uencies %!SO& * Interaural le)el difference at higher fre(uencies %LSO&

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!onaural cues: hori$ontal and )ertical coordinates * Spectral features formed by acoustic reflection patterns * rocessed by neurons sensiti)e to spectral notches

%elated literature Blauert# ens0 Spatial hearing: the psychophysics of human sound locali$ation0 !I press# 377E0 Schnupp# an# Israel en# and Andre' Fing0 Auditory neuroscience: !a>ing sense of sound0 !I ress# /8330 lac># Christopher 0 he sense of hearing0 sychology ress# /83G0 +illiam !0 .artmann0 Signals# sound# and sensation0 Springer Science  Business !edia# 377E0 ul>>i# ille# and !atti Faralainen0 Communication Acoustics: An Introduction to Speech# Audio and sychoacoustics0 ohn +iley  Sons# /83H0 Bear# !0 ?0# Connors# B0 +0# aradiso# !0# Bear# !0 ?0# Connors# B0 +0#  ins0  Ah)eninen# yr>i# elKinen0 sychophysics and neuronal bases of sound locali$ation in humans0 .earing research G8E %/83M&: ;-7E0 Nrothe# Benedi>t# !ichael ec>a# and Da)id !cAlpine0 !echanisms of sound locali$ation in mammals0 hysiological "e)ie's 780G %/838&: 7;G-383/0 a>anen# !ar>o# et al0 1)aluation of sound field synthesis techni(ues 'ith a binaural auditory model0 Audio 1ngineering Society Conference: HHth International Conference: Spatial Audio0 Audio 1ngineering Society# /83M0 a>anen# !ar>o# Olli Santala# and ille ul>>i0 isuali$ation of functional count-comparison-based binaural auditory model output0 .earing research G87 %/83M&: 3ME-3G0 a>anen# !ar>o O0# Olli Santala# and ille ul>>i0 Combining the outputs of functional models of organs responsible for binaural cue decoding0 roceedings of !eetings on Acoustics0 ol0 370