Week 6: (March 15, 2011) Auditory Maps and orienting: need for Coordinate Transformations
Week 6: (March 15, 2011) Auditory Maps and orienting: need for Coordinate Transformations.
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Transcript of Week 6: (March 15, 2011) Auditory Maps and orienting: need for Coordinate Transformations.
Week 6: (March 15, 2011)
Auditory Maps and orienting: need for
Coordinate Transformations
The Barnowl (tyto alba):
Ears are placed asymmetrically
View on left side View on right side
(Takahashi)
Convergence of many ICc neurons onto a single ICx neuron
creates ITD sensitivity
(Takahashi)
Neurons in the owl’s
ventral lemniscus
are sensitive to
the interaural level
difference (ILD)!
(equivalent to the
LSO in mammals)
(Knudsen/Konishi)
Formation of a space-specific neuron in the owl’s ICx:
Convergence of ITD and ILD sensitive neurons
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.....).
General Organization of the Mammalian Auditory System
ACOUSTIC
subcorticalpathways I
The Direct Sound-Localization and Orienting Pathway:
SuperiorColliculus:
eye-headorienting
InferiorColliculus:
sounddirection
Brainstem:
acousticcue
processing
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
SC: Topographic map of gaze - shifts: saccade vectors
time
Firingrate
Hor. Eye Pos
Vert. Eye Pos
Hor. Eye Pos
Independent of eye position
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
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 ’’
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.
Tuningof an IC neuronto eye position.
1. FR increases for rightward eye fixations.
2. FR increases only during the acoustic response:
“GAIN FIELD”
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
Example of a typical IC model neuron: ‘gain field’
Simulation result for TH =(+20,+30)deg and EH =(-30,+30) => ME = (50,0)
M
HE
M = H-E
T
O
F
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
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)
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
Studying coordinate transformations - I
Goossens & Van Opstal, J Neurophysiol 1999
Double-StepParadigm
Pure-ToneLocalizationParadigm
(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
Sound localization responses are spatially accurate
(Goossens and Van Opstal, 1999)
Pure-Tone Localization Behaviour: do head movements help?
Pure-Tone Localization:
(in)dependent of head orientation?
Pure-Tone Localization:
depends onhead orientation
AND
on tonefrequency!
Sounds appear to be represented in a spatial(body-centered) reference frame (TSPACE = THEAD+HSPACE):
Computation WITHIN the (tonotopic) auditory system
Dynamic coordinate transformations for multisensory orienting: