1. #05: ECHOLOCATION IN BATS I
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. #05: ECHOLOCATION IN BATS I
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, 3 examples)
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. 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 ] ) }
... Y-axis
... X-axis
 t   db 
~ 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
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)