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studying barn owls in the laboratory sound intensity cues sound timing cues

PART 2: SENSORY WORLDS #08: PREY LOCATION IN BARN OWLS II. studying barn owls in the laboratory sound intensity cues sound timing cues neural pathways for sound location auditory space interaural time differences delay lines & coincidence detectors

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studying barn owls in the laboratory sound intensity cues sound timing cues

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  1. PART 2: SENSORY WORLDS #08: PREY LOCATION IN BARN OWLS II • studying barn owls in the laboratory • sound intensity cues • sound timing cues • neural pathways for sound location • auditory space • interaural time differences • delay lines & coincidence detectors • visual calibration of the auditory world • summary

  2. PART 2: SENSORY WORLDS #08: PREY LOCATION IN BARN OWLS II • studying barn owls in the laboratory • sound intensity cues • sound timing cues • neural pathways for sound location • auditory space • interaural time differences • delay lines & coincidence detectors • visual calibration of the auditory world • summary

  3. VISUAL CALIBRATION OF THE AUDITORY WORLD • owls are auditory & visual animals • systems integrated  locate source of stimulus • recall experimental set up...

  4. BARN OWLS IN THE LABORATORY • monitor head orientation behavior • used “search coil”  weak electric field • signal magnitude + sign  head position • ~ sounds • no echoes • total darkness • sound & head positions correlated by computer p.64 fig.3.2

  5. BEHAVIORAL ANALYSIS • monaural occlusion experiments  location error • elevation • azimuth (minor) • 2 critical observations... • correction after weeks ? • young owls  yes • old owls  less • remove occlusion • error persists, but... • corrected / time p.67 fig.3.4

  6. BEHAVIORAL ANALYSIS • monaural occlusion experiments  location error • elevation • azimuth (minor) • other cues... vision ? • prisms  correct ~ visual offset p.67 fig.3.4

  7. normal • visual shift only • ...auditory shift • shift remains p.83 fig.3.15 VISUAL vs AUDITORY STIMULI • hypothesis: vision guides evaluation of auditory cues • raised young (sensitive) owls with prisms • do owls adjust auditory targeting ~ visual input ? • results:

  8. VISUAL vs AUDITORY STIMULI • developmental regulation of shift •  7 mo, shift ~ 20° • adults, shift only a few ° • results: • normal • visual shift only • ...auditory shift • shift remains p.83 fig.3.15

  9. NEURAL CORRELATES OF PLASTICITY • convergence: • azimuthal (ITD) & horizontal (ILD) info in ICX • auditory & visual information in optic tectum • receptive fields of optic tectum aligned in columns p.84 fig.3.16

  10. (A) multimodal space map in optic tectum (B) prisms shift visual receptive field (C) + 8 wks... auditory receptive field shifts p.85 fig.3.17 NEURAL CORRELATES OF PLASTICITY • receptive fields of optic tectum aligned in columns

  11. NEURAL CORRELATES OF PLASTICITY • what causes this shift in alignment ? • azimuthal plane... expect • horizontal shift in auditory perceptive fields • induced by abnormal visual cues • accompanied by ~ shift in ITDs of tectal neurons p.85 fig.3.17

  12. (A) optic tectum neurons • normal  visual tuning @ 0 s (center of field) • 8 wks of prism  visual tuning @ ~ 50 s p.86 fig.3.18 (B) optic tectum neuron arrays • shifts follow pattern of visual experience NEURAL CORRELATES OF PLASTICITY • adaptation of ITD map ~ visual experience

  13. p.87 fig.3.19 (A) initial: az.= 0°, ITD = 0 s (B) transition: az., ITD  (C) shift: az.= 23°, ITD = 40 s NEURAL CORRELATES OF PLASTICITY • ITD tuning curves in ICX neurons of prism-reared owls • shaded = normal & learned • 2 stages of ITD adjustment

  14. SENSITIVE PERIOD FOR CALIBRATION • visual experience modification of auditory localization • young < juvenile > adult  60 days 200  • monaural occlusion • displacement prisms • optic tectum ITD tuning (A) juveniles: sensitive to prisms (B) adults: naïve – insensitive to prisms () experienced – sensitive () p.88 fig.3.20

  15. SITES OF ADAPTIVE PLASTICITY • visual horizontal displacement  • auditory space maps • optic tectum ITD map • auditory space maps: ICC ICX  op.tectum p.90 fig.3.21

  16. SITES OF ADAPTIVE PLASTICITY • auditory space maps: ICC ICX  op.tectum • prism reared owls: • ICC map normal • ICX map shifted ~ optic tectum shift • anatomy • normal ICC-ICX input • additional ICC-ICX input to shifted ITD region • accounts for recovery during lifetime  normal • accounts for rapid readjustment  prisms again p.90 fig.3.21

  17. SITES OF ADAPTIVE PLASTICITY • cellular mechanisms ? • involves: • glutamate - excitatory neurotransmitter • glutamate receptor - NMDA receptor p.90 fig.3.21

  18. SUMMARY • experiments identified 2 critical auditory cues... • time info, ITD  NM  azimuthal information • intensity info, ILD  NA  elevation information • parallel processed, cochlear nuclei  ICX • ITD & ILD information  ICX space-specific neurons • each neuron  receptive field in auditory space • emergent / unique property (not signal addition) • coordinated auditory & visual world • visual tuning of auditory space • young / juvenile > adult

  19. SUMMARY • multimodal maps of sensory world in optic tectum • auditory maps can shift  register with visual • young < juvenile > adult • realignment by new ICC  ICX connections • connections persistent

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