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Auditory Neuroscience 1
Spatial Hearing
Systems Biology Doctoral Training Program
Physiology course
Prof. Jan Schnupp
[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)
ILD at 700 Hz
ILD at 11000 Hz
Unlike ITDs, ILDs are highly frequency dependent. At higher sound
frequencies ILDs tend to become larger, more complex, and hence
potentially more informative.
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
Spherical
bushy
cell
Endbulb
of Held
Auditory nerve
fiber
EE neuron
The Jeffress model: mapping ITDs in the brain?
http://auditoryneuroscience.com/to
pics/jeffress-model-animation
ITD tuning varies with sound frequency: no map?
McAlpine and colleagues
x
Corte
x
Corte
MGB
Brainstem Midbrain
The
Auditory
Pathway
MGB
IC
IC
NLL
CN, cochlear nuclei;
Cochlea
SOC, superior olivary complex;
NLL, nuclei of the lateral lemniscus;
IC, inferior colliculus;
MGB, medial geniculate body.
NLL
SOC
CN
SOC
CN
Cochlea
Lesion Studies Suggest Important Role for
A1
Jenkins & Merzenich, J. Neurophysiol, 1984
Binaural Frequency-Time
Receptive Field
Linear
Prediction
of Responses
Input
“i vector”
16
Frequency [kHz]
4
1
16
4
1
Latency
response
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)+ ...
FTRF
“w matrix”
1
0.5
0
200 ms
100
0
-5 0 5 10
dB
Predicting Space from
Spectrum
Left and Right Ear
Frequency-Time Response
Fields
a
Virtual Acoustic
Space Stimuli
16
Frequency [kHz]
4
1
d
Elev[deg]
[deg]
Elev
4
1
c
Schnupp et al Nature 2001
-5 0 5 10
dB
1
0
-60
-180 -120 -60
100
0
e
0.5
0
200 ms
60
rate (Hz)
response
b
C81
16
0
f
60 120 180
Azim [deg]
200
0
0
100
ms 200
“Higher Order” Cortical Areas
In the macaque, primary
auditory cortex(A1) is
surrounded by rostral
(R), lateral (L), caudomedial (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?
Anterolateral
Belt
Caudolateral
Belt
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 posteroparietal cortex.
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.
Artificial Vowel Sounds
/a/
/e/
/u/
/i/
dB
50
200 Hz
0
-50
-100
dB
50
336 Hz
0
-50
-100
dB
50
565 Hz
0
-50
-100
dB
50
951 Hz
0
-50
-100
0
5000
Hz
10000
0
5000
Hz
10000
0
5000
Hz
10000
0
5000
Hz
10000
Bizley et al J Neurosci 2009 29:2064
Responses to Artificial Vowels in Space
Pitch (Hz)
Vowel type (timbre)
Bizley et al J Neurosci 2009 29:2064
Azimuth, Pitch and Timbre Sensitivity in
Ferret Auditory Cortex
Bizley et al J Neurosci 2009 29:2064