Week 6: (March 15, 2011) Auditory Maps and orienting: need for Coordinate Transformations
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Week 6: (March 15, 2011)
Auditory Maps and orienting: need for
Coordinate Transformations
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The Barnowl (tyto alba):
Ears are placed asymmetrically
View on left side View on right side
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(Takahashi)
Convergence of many ICc neurons onto a single ICx neuron
creates ITD sensitivity
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(Takahashi)
Neurons in the owl’s
ventral lemniscus
are sensitive to
the interaural level
difference (ILD)!
(equivalent to the
LSO in mammals)
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(Knudsen/Konishi)
Formation of a space-specific neuron in the owl’s ICx:
Convergence of ITD and ILD sensitive neurons
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The neural map of auditory space in the owl’s ICx
The formation of thiscomputational map depends critically on the quality of the owl’s visual systemthrough feedbackconnections from the SC (later.....).
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General Organization of the Mammalian Auditory System
ACOUSTIC
subcorticalpathways I
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The Direct Sound-Localization and Orienting Pathway:
SuperiorColliculus:
eye-headorienting
InferiorColliculus:
sounddirection
Brainstem:
acousticcue
processing
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Orienting of eyes, head, body (and pinnae)involves the midbrain Superior Colliculus (SC):
SC
EYE
HEAD
VISION
AUDITION
SC:- Multisensory- Sensorimotor ‘interface’- Topographic map of saccadic gaze shifts
‘sensory’ motor
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SC: Topographic map of gaze - shifts: saccade vectors
time
Firingrate
Hor. Eye Pos
Vert. Eye Pos
Hor. Eye Pos
Independent of eye position
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Making an eye movement towards a sound Making an eye movement towards a sound requires a requires a coordinate transformation:coordinate transformation:
This transformation necessiates a signalThis transformation necessiates a signalabout about eye positioneye position re. head, re. head, EE
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C
HEV AV’
Eye and Head Not Aligned
20-2020HE
AV
Eye and Head AlignedA
2
5
10
20
400
-30
30
-60
up
down
rostral
caudal
VA
B
2
5
10
20
40 0-30
30
-60
up
down
rostral
caudal
VA
D
VV ’’
AA ’’
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Jay and Sparks(1984/1987):
Auditory respon-ses in SC arein eye-centeredeye-centeredcoordinatescoordinates.
Question:Question:How do these cells get theirinformation?
Hypothesis:Hypothesis:The midbrain IC could convey thissignal.
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Tuningof an IC neuronto eye position.
1. FR increases for rightward eye fixations.
2. FR increases only during the acoustic response:
“GAIN FIELD”
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Neural Network Model of IC-SC mapping
Sound level and sound positionmodulation
Activity of model IC neurons:
are randomly distributed across the IC population(240 IC neurons, 12 freq bands; 100 SC neurons in map).
Peak GaussianTuning Curve
Eye positionmodulation
Brainstem pathways
Topographic codeof eye-motor error
Tonotopic code of sounds
SCICHRTF/ILDsound at (AZ,EL)
freqfreq
freq
Eye position
Up
Down
Hor
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Example of a typical IC model neuron: ‘gain field’
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Simulation result for TH =(+20,+30)deg and EH =(-30,+30) => ME = (50,0)
M
HE
M = H-E
T
O
F
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OMR+
+
+BodyBody
HeadHead
EyeEye
TargetAudition: Audition: Target re. HeadTarget re. Head
Vision: Vision: Target re. EyeTarget re. Eye
Somatosensation:Somatosensation:Target re. BodyTarget re. Body
Eyere. Head
Headre. Body
Reference frames: including the head and bodyReference frames: including the head and body
Eye movements require oculocentric error signals
Head movements require craniocentric error signals
Vision is Eye-CenteredVision is Eye-Centered
Audition is Head-CenteredAudition is Head-Centered
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In head-free head-free orienting(human):
EyesEyes(Go)and headhead(Ho)indeedmove bothboth toward a visual or auditory target.
Goossens & Van Opstal, Exp. Brain Research, 114 (1997)
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Studying coordinate transformations - I:
Does the auditory system keep sounds in head-centered coordinates?
First, the rationale behind the underlying idea:
“the double-step paradigm and
pure-tone localization”
Goossens and Van Opstal, J Neurophysiol 1999
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Studying coordinate transformations - I
Goossens & Van Opstal, J Neurophysiol 1999
Double-StepParadigm
Pure-ToneLocalizationParadigm
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(V)
(S)
The sound-localization system should be ableto account for intervening movements of theeyes and head:
S
TH
S
F Azimuth
Elevation
Gaze shift
∆G
GSGH
V
GH=TH GS=TH - ∆G
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Sound localization responses are spatially accurate
(Goossens and Van Opstal, 1999)
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Pure-Tone Localization Behaviour: do head movements help?
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Pure-Tone Localization:
(in)dependent of head orientation?
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Pure-Tone Localization:
depends onhead orientation
AND
on tonefrequency!
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Sounds appear to be represented in a spatial(body-centered) reference frame (TSPACE = THEAD+HSPACE):
Computation WITHIN the (tonotopic) auditory system
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Dynamic coordinate transformations for multisensory orienting: