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Auditory Neuroscience 1Spatial Hearing
Systems Biology Doctoral Training ProgramPhysiology course
Prof. Jan [email protected]
HowYourBrainWorks.net
Hearing: an impossible task!
http://auditoryneuroscience.com/foxInSnow
Interaural Time Difference (ITD) Cues
ITD
ITDs are powerful cues to sound source direction, but they are ambiguous (“cones of confusion”)
Front-Back Ambiguity and Phase Ambiguity
http://auditoryneuroscience.com/ear/bm_motion_2
Interaural Level Cues (ILDs)
Unlike ITDs, ILDs are highly frequency dependent. At higher sound frequencies ILDs tend to become larger, more complex, and hence potentially more informative.
ILD at 700 Hz
ILD at 11000 Hz
Spectral (Monaural) Cues
Adapting to Changes in Spectral Cues
Hofman et al. made human volunteers localize sounds in the dark, then introduced plastic molds to change the shape of the concha. This disrupted spectral cues and led to poor localization, particularly in elevation.
Over a prolonged period of wearing the molds, (up to 3 weeks) localization accuracy improved.
EI neuron
Phase locking improves in the cochlear nucleus
Sphericalbushy
cell
Sphericalbushy
cell
Endbulbof Held
Endbulbof Held
Auditory nervefiber
Auditory nervefiber
EE neuron
The Jeffress model: mapping ITDs in the brain?
http://auditoryneuroscience.com/topics/jeffress-model-animation
ITD tuning varies with sound frequency: no map?
McAlpine and colleagues
The Auditory Pathway
M GB
IC
NLL
SOC
CN
Cor
tex
C och lea
M GB
IC
NLL
SOC
CN
Cortex
C och lea
Bra
inst
emM
idbr
ain
CN, cochlear nuclei; SOC, superior olivary complex; NLL, nuclei of the lateral lemniscus; IC, inferior colliculus; MGB, medial geniculate body.
Lesion Studies Suggest Important Role for A1
Jenkins & Merzenich, J. Neurophysiol, 1984
Binaural Frequency-Time Receptive Field
Linear Prediction
of Responses
-5 0 5 10
1
4
16
dB
1
4
16
Fre
qu
enc
y [k
Hz]
r(t) = i1(t-1) w1(1) + i1(t-2) w1(2)+ ...+ i2(t-1) w2(1) + i2(t-2) w2(2)+ ...+ i3(t-1) w3(1) + i2(t-2) w3(2)+ ...
Latency
FTRF “w matrix”
Input“i vector”
01002000
0.5
1re
spo
nse
ms
01002000
0.5
1
resp
on
se
ms 0 100 2000
200
rate
(H
z)
ms
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1
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dB
1
4
16
Left and Right Ear Frequency-Time Response
FieldsVirtual Acoustic Space Stimuli
Fre
qu
en
cy
[kH
z]
a
c
d
e
f
b
C81
-180 -120 -60 0 60 120 180Azim [deg]
-60
0
60
Ele
v [d
eg]
Ele
v [
deg
]
Predicting Space from Spectrum
Schnupp et al Nature 2001Schnupp et al Nature 2001
“Higher Order” Cortical Areas
In the macaque, primary auditory cortex(A1) is surrounded by rostral (R), lateral (L), caudo-medial (CM) and medial “belt areas”.
L can be further subdivided into anterior, medial and caudal subfields (AL, ML, CL)
Are there “What” and “Where” Streams in Auditory Cortex?
Some reports suggest that anterior cortical belt areas may more selective for sound identity and less for sound source location, while caudal belt areas are more location specific.
It has been hypothesized that these may be the starting positions for a ventral “what” stream heading for inferotemporal cortex and a dorsal “where” stream which heads for postero-parietal cortex.
AnterolateralBeltAnterolateralBelt
CaudolateralBeltCaudolateralBelt
A “Panoramic” Code for Auditory Space?
Middlebrooks et al.found neural spike patterns to vary systematically with sound source direction in a number cortical areas of the cat (AES, A1, A2, PAF).
Artificial neural networks can be trained to estimate sound source azimuth from the neural spike pattern.
Spike trains in PAF carry more spatial information than other areas, but in principle spatial information is available in all auditory cortical areas tested so far.
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dB/a/ /e/ /u/ /i/
200 Hz
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dB
336 Hz
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565 Hz
0 5000 10000-100
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50
dB
Hz0 5000 10000
Hz0 5000 10000
Hz0 5000 10000
Hz
951 Hz
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200 Hz
-100
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50
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336 Hz
-100
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565 Hz
0 5000 10000-100
-50
0
50
dB
Hz0 5000 10000
Hz0 5000 10000
Hz0 5000 10000
Hz
951 Hz
Artificial Vowel Sounds
Bizley et al J Neurosci 2009 29:2064Bizley et al J Neurosci 2009 29:2064
Responses to Artificial Vowels in Space
Pit
ch (
Hz)
Vowel type (timbre)
Bizley et al J Neurosci 2009 29:2064Bizley et al J Neurosci 2009 29:2064
Azimuth, Pitch and Timbre Sensitivity in Ferret Auditory Cortex
Bizley et al J Neurosci 2009 29:2064Bizley et al J Neurosci 2009 29:2064