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pt 2: sensory input ch 2: echolocation in bats bat behavior decoding the acoustic environment hunting bats neural m

PART 2: SENSORY WORLDS #05: ECHOLOCATION IN BATS I. pt 2: sensory input ch 2: echolocation in bats bat behavior decoding the acoustic environment hunting bats neural mechanisms moth responses to predation summary . PART 2: SENSORY WORLDS #05: ECHOLOCATION IN BATS I.

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pt 2: sensory input ch 2: echolocation in bats bat behavior decoding the acoustic environment hunting bats neural m

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  1. PART 2: SENSORY WORLDS #05: ECHOLOCATION IN BATS I • pt 2: sensory input • ch 2: echolocation in bats • bat behavior • decoding the acoustic environment • hunting bats • neural mechanisms • moth responses to predation • summary

  2. PART 2: SENSORY WORLDS #05: ECHOLOCATION IN BATS I • pt 2: sensory input • ch 2: echolocation in bats • bat behavior • decoding the acoustic environment • hunting bats • neural mechanisms • moth responses to predation • summary

  3. SENSORY INPUT 2: SENSORY INPUT 3: CENTRAL PROCESSING 4: MOTOR OUTPUT BEHAVIOR

  4. SENSORY INPUT 2: SENSORY INPUT 3: CENTRAL PROCESSING 4: MOTOR OUTPUT BEHAVIOR

  5. SENSORY INPUT • behavior driven by sensory stimuli • external • internal • survival needs • foraging (feeding, predation) • shelter (environment, predators) • reproduction • nervous system evolution  specialization for each environment  adaptive behavior

  6. SENSORY INPUT • pt 2: sensory worlds... • how nervous systems process sensory information (2 modalities, 3examples) • auditory • ch 2: echolocation in bats • ch 3: prey location in barn owls • visual • ch 4: feature analysis in toads

  7. SENSORY MODALITIES • somatosensory • visceral • special

  8. SENSORY MODALITIES • somatosensory • touch • temperature • pressure • pain • proprioception • visceral • special

  9. SENSORY MODALITIES • somatosensory • visceral • osmolarity • pressure • specific chemicals • temperature • special

  10. SENSORY MODALITIES • somatosensory • visceral • special • olfaction • gustation • audition • vision • pheromone

  11. SENSORY MODALITIES • somatosensory • visceral • special • olfaction • gustation • audition • vision • pheromone

  12. ECHOLOCATION IN BATS • Mammalian order Chiroptera (2nd most numerous) • only true flying mammals (flying squirrels glide) • most nocturnal • 2 suborders • Megachiroptera: ~ 150 spp, “big” (eg, flying fox) • Microchiroptera: ~ 800 spp, “small” • near cosmopolitan distribution • many foraging specializations, reflecting... • wide range of diet, many insectivorous

  13. ECHOLOCATION IN BATS • foraging specializations of insectivorous bats • outstanding fliers: agile, fast

  14. ECHOLOCATION IN BATS • foraging specializations of insectivorous bats • outstanding fliers: agile, fast • eat a LOT (100s) of insects / day

  15. ECHOLOCATION IN BATS • foraging specializations of insectivorous bats • outstanding fliers: agile, fast • eat a LOT (100s) of insects / day • echolocation, 2 types • passive: listen only (stealthy) • active: emit ultrasonic pulses, analyze reflection

  16. ECHOLOCATION IN BATS • documented observations for centuries • Spallanzini (1794) studied mechanism of navigation • deprived vision  no problems • deprived hearing  failed to navigate

  17. ECHOLOCATION IN BATS • Griffin (+ colleagues, 1938...) “bat detector” • listening device for high frequency sound • flying bats emit pulses (field & lab), use to • navigate & capture prey... “echolocation” • navigate a web of nylon fishing line in dark lab • block auditory signal (2 ways) impaired function • discriminate thrown edible items from non-edible • pulse frequency (Hz) 1/ object range • flight: 10 – 30 kHz,  object: 50 – 250 kHz

  18. ECHOLOCATION IN BATS • echolocating bat capturing a prey item (meal worm)

  19. DECODING THE ACOUSTIC ENVIRONMENT • bats use echolocation to discriminate object... • position • size • texture • movement • ~ we use vision • how is this achieved ? • what features of sound are used ?

  20. ... Y-axis ... X-axis }  db  t  DECODING THE ACOUSTIC ENVIRONMENT • physical aspects of sound & sound modulation • amplitude ( = volume, decibels [ db ] ) • frequency ( = pitch, cycles/s [ kHz ] ) • pulse duration ( time [ t ] ) • interpulse interval ( time [ t ] ) • ~ light and vision

  21. DECODING THE ACOUSTIC ENVIRONMENT • 2 functions necessary for active echolocation • sending • receiving • 2 mechanisms linked by... • purpose (why) • co-evolution or independent events ? • nervous system (how)

  22. DECODING THE ACOUSTIC ENVIRONMENT • bats emit 2 types of ultrasonic signals • frequency-modulated (FM) sweep • constant frequency (CF)

  23. DECODING THE ACOUSTIC ENVIRONMENT • bats emit 2 types of ultrasonic signals • frequency-modulated (FM) sweep or broadband • short pulse (<5 ms) • range of frequencies (100 Hz –25 kHz) • eg, big brown bat (Eptesicus)

  24. DECODING THE ACOUSTIC ENVIRONMENT • bats emit 2 types of ultrasonic signals • constant frequency (CF) • longer pulse (5 –30 ms) • ~ no frequency modulation • eg, horseshoe bat (Rhinolophus)

  25. DECODING THE ACOUSTIC ENVIRONMENT • bats emit 2 types of ultrasonic signals • frequency-modulated (FM) sweep or broadband • constant frequency (CF) • combined FM-CF pulses  3rd signal category

  26. DECODING THE ACOUSTIC ENVIRONMENT • bats use 2 additional features of emitted sound • fundamental frequencies + harmonics • pulse rate (rate  as distance )

  27. DECODING THE ACOUSTIC ENVIRONMENT • target information obtained through echolocation • distance • subtended angles (angular size) • absolute size • azimuth (lateral position ~ receiver) • elevation • velocity

  28. DECODING THE ACOUSTIC ENVIRONMENT • target information obtained through echolocation • distance • time between pulse emitted & echo received • rapid FM sweeps • gives other info as well • pulse-echo determination at >> frequencies

  29. DECODING THE ACOUSTIC ENVIRONMENT • distance information obtained through echolocation • test echo-delay theory • train bats to feed at different perches (A) • can discriminate very short distances (5 cm)

  30. DECODING THE ACOUSTIC ENVIRONMENT • distance information obtained through echolocation • test echo-delay theory • replayed phantom echos with variable delays (B) • correct choice of phantom target • discriminate 60 s ~ 10 – 15 mm • delay ~ distance  • very accurate !

  31. DECODING THE ACOUSTIC ENVIRONMENT • target information obtained through echolocation • subtended angle or angular size (size component) • loudness or amplitude of echo • amplitude can  when target • large but distant • small but near

  32. DECODING THE ACOUSTIC ENVIRONMENT • target information obtained through echolocation • absolute size • computed from • distance (pulse-echo delay) • angular size (amplitude)

  33. DECODING THE ACOUSTIC ENVIRONMENT • target information obtained through echolocation • azimuth • computed from binaural cues • compare delays received in both ears ~ triangulation • some information processed in each ear

  34. DECODING THE ACOUSTIC ENVIRONMENT • target information obtained through echolocation • elevation • computed from two cues, compare echos received when • ears are moved to various positions • ear flaps in pinnae are opened variably

  35. DECODING THE ACOUSTIC ENVIRONMENT • target information obtained through echolocation • velocity, absolute & relative to self • computed from Doppler shift of echo frequency • sound frequency perceived (by the bat) shifts •  on approach, waves “compress” •  on retreat, waves “expand”

  36. DECODING THE ACOUSTIC ENVIRONMENT • target information obtained through echolocation • velocity, absolute & relative to self • CF suited for Doppler analysis • long pulses (10 – 100 ms) • “narrow band” (not FM) • higher energy  locate distant targets • acoustic fovea  auditory system sensitive to narrow band width around CF signals

  37. DECODING THE ACOUSTIC ENVIRONMENT • Doppler analysis: Doppler shift compensation • Rhinolophus CF signal & acoustic fovea both tuned  ~ 83 kHz • Doppler shifted echo ~ 83  87 kHz in flight • Doppler shift compensation = bat lowers CF frequency  echo ~ 83 kHz • echo returns in sensitive range, more easily distinguished from call at less audible frequency

  38. DECODING THE ACOUSTIC ENVIRONMENT • Doppler analysis: Doppler shift compensation • mustached bat CF signal & acoustic fovea both tuned  ~ 61 kHz • bat on swing • DSC occurs when swinging forward only

  39. DECODING THE ACOUSTIC ENVIRONMENT • Doppler analysis: target flutter • generated by flying insects • accoustic glint from reflected signal @ 90° ~ insect wing • weak echo from  angles • echo subtle frequency & amplitude modulation • horseshoe bat can discriminate 30 cycles/s (eg 83,000 Hz vs 83,030 Hz)

  40. DECODING THE ACOUSTIC ENVIRONMENT • Doppler analysis: target flutter • stationary horseshoe bats  long CF for flutter only • then track position and capture prey  FM

  41. DECODING THE ACOUSTIC ENVIRONMENT • pulse-echo delay analysis: jitter • variation of playback expt. • train bat to detect target that appears to rapidly switch between 2 distances (jitters) • reduce intervals between jitters, measured threshold for perceiving such movements

  42. DECODING THE ACOUSTIC ENVIRONMENT • pulse-echo delay analysis: jitter • bats could perceive delay  10 – 12 ns... • ~ 2 m distances • bats may use such acute temporal resolution in signal perception to characterize fine-grained target texture

  43. HUNTING BATS • stroboscopic images of hunting bats • 3 stages of hunting and capture • search • approach • terminal

  44. HUNTING BATS • stroboscopic images of hunting bats • 3 stages of hunting and capture • search  habitat-dependent • FM in clutter, distance info • CF in open, long range

  45. HUNTING BATS • stroboscopic images of hunting bats • 3 stages of hunting and capture • approach • orient toward target •  pulse rate (~50/s) • CF  FM

  46. HUNTING BATS • stroboscopic images of hunting bats • 3 stages of hunting and capture • terminal •  pulse rate • FM bats (~200/s) • CF bats (~100/s)

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