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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 right side. View on left side. Convergence of many ICc neurons onto a single ICx neuron creates ITD sensitivity. (Takahashi).

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Week 6: (March 15, 2011) Auditory Maps and orienting: need for Coordinate Transformations

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  1. Week 6: (March 15, 2011)Auditory Maps and orienting: need forCoordinate Transformations

  2. The Barnowl (tyto alba): Ears are placed asymmetrically View on right side View on left side

  3. Convergence of many ICc neurons onto a single ICx neuron creates ITD sensitivity (Takahashi)

  4. Neurons in the owl’s ventral lemniscus are sensitive to the interaural level difference (ILD)! (equivalent to the LSO in mammals) (Takahashi)

  5. Formation of a space-specific neuron in the owl’s ICx: Convergence of ITD and ILD sensitive neurons (Knudsen/Konishi)

  6. The neural map of auditory space in the owl’s ICx The formation of this computational map depends critically on the quality of the owl’s visual system through feedback connections from the SC (later.....).

  7. I subcortical pathways ACOUSTIC General Organization of the Mammalian Auditory System

  8. The Direct Sound-Localization and Orienting Pathway: Superior Colliculus: eye-head orienting Brainstem: acoustic cue processing Inferior Colliculus: sound direction

  9. Orienting of eyes, head, body (and pinnae) involves the midbrain Superior Colliculus (SC): motor ‘sensory’ EYE VISION SC HEAD AUDITION SC: - Multisensory - Sensorimotor ‘interface’ - Topographic map of saccadic gaze shifts

  10. Vert. Eye Pos Hor. Eye Pos Hor. Eye Pos Firing rate Independent of eye position time SC: Topographic map of gaze - shifts: saccade vectors

  11. Making an eye movement towards a sound requires a coordinate transformation: This transformation necessiates a signal about eye position re. head, E

  12. C A Eye and Head Aligned Eye and Head Not Aligned AV’ V -20 20 20 E H A’ V’ B D rostral rostral up up 2 2 5 AV 5 V E H 10 A V 10 A 20 30 20 30 down 0 down 40 -30 40 0 -60 -30 caudal -60 caudal

  13. Jay and Sparks (1984/1987): Auditory respon- ses in SC are in eye-centered coordinates. Hypothesis: The midbrain IC could convey this signal. Question: How do these cells get their information?

  14. Tuning of an IC neuron to eye position. 1. FR increases for rightward eye fixations. 2. FR increases only during the acoustic response: “GAIN FIELD”

  15. Eye position HRTF/ILD sound at (AZ,EL) IC SC Up Hor freq Down freq freq Brainstem pathways Tonotopic code of sounds Topographic code of eye-motor error Activity of model IC neurons: are randomly distributed across the IC population (240 IC neurons, 12 freq bands; 100 SC neurons in map). Neural Network Model of IC-SC mapping Peak Sound level and sound position modulation Eye position modulation Gaussian Tuning Curve

  16. Example of a typical IC model neuron: ‘gain field’

  17. M F T H E O M = H-E Simulation result for TH =(+20,+30)deg and EH =(-30,+30)=> ME = (50,0)

  18. Vision: Target re. Eye OMR Eye Vision is Eye-Centered + Eye re. Head Target Head + Audition: Target re. Head Audition is Head-Centered Head re. Body Somatosensation: Target re. Body + Body Eye movements require oculocentric error signals Head movements require craniocentric error signals Reference frames: including the head and body

  19. In head-free orienting(human): Eyes(Go)and head(Ho)indeed move both toward a visual or auditory target. Goossens & Van Opstal, Exp. Brain Research, 114 (1997)

  20. 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

  21. Studying coordinate transformations - I Double-Step Paradigm Pure-Tone Localization Paradigm Goossens & Van Opstal, J Neurophysiol 1999

  22. Elevation S S GS GH ∆G F Azimuth Gaze shift V The sound-localization system should be able to account for intervening movements of the eyes and head: (S) TH (V) GS=TH - ∆G GH=TH

  23. Sound localization responses are spatially accurate (Goossens and Van Opstal, 1999)

  24. Pure-Tone Localization Behaviour: do head movements help?

  25. Pure-Tone Localization: (in)dependent of head orientation?

  26. Pure-Tone Localization: depends on head orientation AND on tone frequency!

  27. Sounds appear to be represented in a spatial (body-centered) reference frame (TSPACE = THEAD+HSPACE): Computation WITHIN the (tonotopic) auditory system

  28. Dynamic coordinate transformations for multisensory orienting:

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