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

PART 2: SENSORY WORLDS #07: PREY LOCATION IN BARN OWLS I. 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 #07: PREY LOCATION IN BARN OWLS I • 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 #07: PREY LOCATION IN BARN OWLS I • 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. AUDITORY CUES Intensity differences high frequency ... short wavelength Timing differences low frequency ... long wavelength

  4. BARN OWL BIOLOGY • Tyto alba, hunt using auditory cues • height: 1-1.5 ft • wing span: 3 ft • velocity: 4-8 m/s • forms pair bonds • hunting nocturnal & crepuscular • small rodents > other small animals • prey of great horned owls  restricts barn owl hunting to deep night

  5. BARN OWL BIOLOGY • Tyto alba, hunt using auditory cues • locates prey in space • horizontal • vertical • relative to self • prey capture... FIG 1 • how to determine the cues? • not visual (test in dark) • heat, olfactory, auditory ? • early mouse/paper expt. p.63 fig.3.1

  6. BARN OWLS IN THE LABORATORY • 1st important behavioral observation... • owls turn their heads rapidly toward sound • bring source to center • tested experimentally... p.63 fig.3.1

  7. 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

  8. BARN OWLS IN THE LABORATORY • features of barn owl auditory system • face covered with rows of stiff feathers... facial ruff • sound-collecting surface  auditory canals • ears asymmetrical • right ear & opening directed , sensitivity  head • left ear & opening directed , sensitivity  head

  9. BARN OWLS IN THE LABORATORY • 2D mapping of sound dimensions • azimuth  horizontal • elevation  vertical • can target sound within 1°-2° • 3x human accuracy in vertical dimension p.65 fig.3.3

  10. BARN OWLS IN THE LABORATORY • 2D mapping of sound dimensions • most sensitive to sound in front • frequency range 100 Hz - 12 kHz • azimuth: accurate within 1 - 9 kHz • elevation: accurate within 3 - 10 kHz p.65 fig.3.3

  11. BARN OWLS IN THE LABORATORY • experiments identified 2 critical auditory cues... • sound intensity cues  elevation dimension • sound timing cues  azimuth dimension

  12. SOUND INTENSITY CUES • attenuated sound, blocking ears with 2 types of plugs • soft  modest • hard  severe • sound location... • recall that the ears are asymmetrical... • right ear & opening directed , sensitivity  head • left ear & opening directed , sensitivity  head • interaural intensity differences to target elevation, also called interaural level differences (ILD)

  13. SOUND INTENSITY CUES • attenuated sound, blocking ears with 2 types of plugs • soft  modest • hard  severe • sound location error... • elevation • some azimuth • not sufficient to explain accuracy p.67 fig.3.4

  14. SOUND INTENSITY CUES • removed facial ruff • sound location error... • mostly elevation (head oriented @ horizontal plane) • azimuth OK • ruff amplifies directional asymmetry of ears

  15. SOUND TIMING CUES • sounds arrive @ different times to each ear • difference in time = temporal disparity • barn owls can distinguish 10 ms temporal disparity • interaural time difference (ITD) • use ITD for azimuthal sound source determinations p.68 fig.3.5a

  16. p.68 fig.3.5b SOUND TIMING CUES • sounds arrive @ different times to each ear • 2 types of temporal disparity • transient (onset / offset) • ongoing • can use both • which is used ?

  17. SOUND TIMING CUES • implanted miniature speakers  decouple disparities • measured orientation ~ ongoing temporal disparity • range of 10 - 80 s • head movement to target represented by disparity • orientation not ~ transient disparity p.69 fig.3.6

  18. NEURAL PATHWAYS FOR SOUND LOCALIZATION • anatomical structures • basilar mem. / inner ear • frequency coding • phase locking • intensity coding • cranial nerve VIII • cochlear nuclei • NA • NM p.71 fig.3.7

  19. NEURAL PATHWAYS FOR SOUND LOCALIZATION • anatomical structures • cochlear nuclei • NA • NM • NL • LL • higher auditory centers • ICC (~ mam. IC) • ICX p.71 fig.3.7

  20. AUDITORY SPACE • external nucleus (ICX) neuron response • frontal sound • ICX space- specific neurons p.72 fig.3.8a

  21. AUDITORY SPACE • external nucleus (ICX) neuron response • frontal sound • ICX space- specific neurons • map p.72 fig.3.8b

  22. AUDITORY SPACE • external nucleus (ICX) neuron response • frontal sound • ICX space-specific neurons • map • 2nd roving speaker • excitatory (peaks) & inhibitory (trough) regions p.73 fig.3.9

  23. • ITD ~ 32 s  • ILD ~ 11 dB •  2D field p.74 fig.3.10 AUDITORY SPACE • space-specific neurons are binaural • driven by bilateral stimuli • response ILD & ITD specific • eg, neuron peak response...

  24. AUDITORY SPACE • cochlear nuclei  ICX • NM  time info • ITD  azimuth • phase sensitive • intensity sensitive • NA  intensity info • ILD  elevation • intensity sensitive p.71 fig.3.7

  25. AUDITORY SPACE • cochlear nuclei  ICX... parallel pathways ? • inject reversible local anesthetics, record from space-specific ICX neuron, sound target stimuli •  NM • disruption selectivity for time disparity • no effect on level disparity •  NA • disruption selectivity for level disparity • no effect on time disparity

  26. INTERAURAL TIME DIFFERENCES • Jeffress’s neuronal circuit model for encoding time • coincidence detector  C • fires best with L & R coincident signals • delay line  L (eg) • codes R delay p.77 fig.3.11

  27. INTERAURAL TIME DIFFERENCES • Konishi model built on Jeffress for encoding ITD • coincidence detector • neuron arrays • variable delays • features • encodes ITD • neurons encode different ITDs • but... = output • ITD place code p.78 fig.3.12

  28. DELAY LINES & COINCIDENCE DETECTORS • does the owl use this mechanism ? ... evidence • anatomy... • NM  NL (putative neural substrate for model) • ipsilateral & contralateral innervation of NL • innervation parallel p.79 fig.3.13

  29. DELAY LINES & COINCIDENCE DETECTORS • does the owl use this mechanism ? ... evidence • physiology... • NL neurons phase-lock to binaural stimuli • delay  asymmetry • delay ~ temp. disparity • NL neurons = coincidence detectors p.79 fig.3.13

  30. DELAY LINES & COINCIDENCE DETECTORS • does the owl use this mechanism ? ... evidence • anatomy + physiology... • each ITD encoded by different delays • space-specific neurons • NL position info  ICX p.80 fig.3.14

  31. DELAY LINES & COINCIDENCE DETECTORS • does the owl use this mechanism ? ... evidence • anatomy + physiology... • each ITD encoded by different delays • space-specific neurons • NL position info  ICX p.71 fig.3.7

  32. DELAY LINES & COINCIDENCE DETECTORS • ILD (intensity) processing ? ... • poorly understood • v. nuc. lat. lemniscus • spatial organization ~ ICX • bicoordinate signatures not yet elucidated p.71 fig.3.7

  33. sensory  motor • br stem tegmentum • 3D map of head position • distinct circuits sensory motor AUDITORY SPACE • integration with other sensory input • ICX  optic tectum sensory space maps • optic tectum  brain stem p.84 fig.3.16

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