1. Finish Ch 5 Sound propagation Ch 6 : Sound reception 2/10/11
Lecture #5
Finish Ch 5 Sound propagation
Ch 6 : Sound reception
2/10/11

2. Next few classes Finish sound today Next week Start light and vision
Tuesday I am away - Adam Smith will give intro light lecture
Problem set is due Thursday 2/17

3. Ch. 5 Sound propagation Distortions altering frequency domain
Distortions altering time domain
What’s a signaller to do?

4. Distortions modifying frequency spectrum
Global attenuation
Pattern loss
Differential medium absorption
Scattering
Boundary reflections
Refraction
Addition of noise

5. B. Distortions modifying time domain
Global attenuation
Same as for frequency - decreases with distance
Pattern loss
Addition of noise
Alters temporal pattern of sound

6. Pattern loss from reverberations
Multiple paths between sender and receiver
Echoes from boundaries and scattering
Especially a problem in forests
Low freq (<1 kHz) reflect off canopy, ground
High freq (>3 kHz) reflect off foliage
So what is best freq for communication?
Best is freq btn 1 and 3 kHz - so that is often range used by birds

7. Reverberations Echoes arrive later and with lower amplitude
Even worse in water than air because sound travels farther
Sender’s signal Received signal
In air, reverberation is 1/2 signal after 100 ms. So don’t want to modulate faster than 10 Hz as need time for reverb to decrease.

8. Pattern loss from added modulations
Wind and density gradients can modulate amplitudes
In open grasslands, occur at freq < 10 Hz
So animal wanting to modulate its signal should do so > 10 Hz

9. Pattern loss from added modulations
Wind and density gradients can modulate amplitudes
In open grasslands, wind modulates at freq < 10 Hz
So animal wanting to stand out should modulate its signal > 10 Hz
> 100 ms
Wind
Animal

10. Pattern loss from added modulations
Reverberations in forest
Reverberation takes ~100 ms to fade
So animal wanting to stand out should modulate its signal < 10 Hz
Want to wait till after reverberation dies out so slow modulation is best
> 100 ms
Animal

11. How to design the perfect terrestrial signal
Global attenuation
Reflection / Refraction

12. Boundary reflections Avoid lower frequencies which are in the notch
fd=c/(2D)
Avoid lower frequencies which are in the notch
Boundary wave can be sound absorbed by ground, travels along and then reradiates
Can also be surface wave just on surface of ground
All sounds combine additively at receiver. Can get constructive and destructive interference.

13. Pattern loss from refraction
Temperature gradients cause air density gradients - Sound will bend
Day Night
On right, at night, ground temp cools quickly leaving warmer layer of air up above. Then sound velocity and Z is low close to ground and sound will cross into higher Z as it goes up. As a result, sound will be bent back towards the ground. This creates a sound channel close to the ground so sound does not penetrate the upper air layers.
Also occurs in closed forest where canopy warmed by sun creates a warm layer.

14. How to design the perfect terrestrial signal
Global attenuation
- increase amplitude
- emit from location with max propagation
Reflection / Refraction
- Call early when low wind and temps
Call from open location in high location
Call between ground and canopy to utilize sound channel

15. Best terrestrial frequencies?

16. Best terrestrial frequencies?
Complex frequency signals will have each freq range distorted differently so want simple frequency
High freq are lost due to absorption and scattering
Close to ground, low frequency notch cuts out frequencies

17. Best terrestrial frequencies?
Another consideration
Wavelengths > 2-5 body size are hard to generate
For high intensity, want wavelength less than this
Body Max  Min freq
Frog 10 cm 20 cm 1.7 kHz
Bird 20 cm 40 cm 850 Hz

18. Tradeoffs Easier to generate high frequency (short wavelength)
Easier to propagate low frequency
So best compromise is in middle 1-6 kHz

19. 0.5 - 5 kHz is where noise is lowest

20. How do animals distinguish their sound?
Species specific modulation
In forests, modulate < 10 Hz
In grasslands, modulate > 10 Hz

21. Difference btn forest and grassland calls
A B chingalo sparrow - slower trills in forest
C D great tits - rapid freq mod in grasslands

22. Ch. 6 Sound reception Coupling sound to organisms
Modification and analysis of sound vibrations
Ears

23. Ideal receiver
What does an ideal receiver want to detect?

24. Ideal receiver Wide range of detectable frequencies
Frequency range
Wide range of detectable amplitudes
Dynamic range
Fine frequency resolution, f
Fine temporal resolution, t
Accurate measurement of amplitudes
Accurate localization of sound source in vertical and horizontal planes
Accurate determination of distance to source
Ability to detect rapid time domain changes - pattern recognition
Impossible to optimize detection of all sound features. Evolution favors one over another
Physical limit : because f = 1/t there is a trade off between these two

25. Coupling sound to organisms
Difficult to transfer sound from air to an organism
Need some coupling system to do that
Ideal coupler
Transfer a large fraction of sound energy to detector organs
Preserve amplitude, phase, frequency and directional information

26. Coupling sound to organisms
Three different ways
1. Particle detectors
2. Pressure detectors
3. Pressure-differential detectors

27. 1. Particle detectors
Fig 6.1
Long structure which is moved by sound pressure waves
This stretches and compresses sensory cells attached to base of structure
Antennal arista of fruit fly, B) trichoid sensilla on cockroach cercus (so fine airs are sound sensors-diff lengths to sense diff freqs)
C) Antenna of male mosquito; D) trichobothrium of spider

28. Sound sensing hairs arista Male mosquito
Drosophila arista
Male mosquito antennae
Spider trichobothria:
Male
mosquito

29. Particle detectors
Frequency response requires hairs to oscillate in phase with particles of media
Need to be light
Even smallest hairs can’t move faster than 1 kHz
Long hairs give good sensitivity
Long moment arm to detect small motion
Harder to use in water
Sometimes attach large masses to ends of hair
Mosquito antenna is as sensitive as human ear (0 dB SPL)

30. Particle detectors are directional
No hair motion for motion along it’s axis
Only detect motion perpendicular to hair
Can use multiple hairs pointing in diff directions to sense directionality of sound

31. Cartoon of cricket and cockroach antennal cerca
Detect wind motion along arrow directions

32. 2. Pressure detectors Use membrane (tympanum) to detect pressure
Tympanum stretched over hollow cavity
Bends away from higher pressure
Couple tympanum bending to sensory cell

33. Tympanum helps couple in sound
Light membrane has closer impedance to air than body
Captured sound = pressure * area
Large membrane captures more sound
Rapid response

34. Other structures Pinna - provides directionality to sound detection
Best for wavelengths smaller than size of pinna
Auditory meatus
Funnel shaped tube to more efficiently collect sound

35. Directionality Best if have two ears to determine sound direction
Use time difference in arrival of some key sound feature
Arrival time difference must be large enough that brain can resolve it

36. Arrival times of sound coming from different direction
Left ear Right ear

37. Arrival time depends on head size
Try class demo - identify 4 clickers. Have everyone else close their eye. Point to each of the 4 in turn and have them make a sound and then have class see if can tell where it came from.
Human time delay is 0.5 msec based on head size
Less time delay available in water because of faster sound velocity.
Owls devote enough neurons to resolve msec time differences.

38. Pressure-differential detectors
Sample sound on both sides of tympanum
Two sounds will be out of phase and tympanum will respond to pressure difference

39. Pressure-differential detectors
Force on the tympanum
is angle btn sound and tube, so strong angular dependence to response L
A = surface area of membrane  is wavelength cos  is angle between tube and sound direction
P is incident sound pressure L is extra distance sound travels (length of tube)

40. Pressure-differential detectors
Force on the tympanum
F is inverse with  so not great for low frequencies
A = surface area of membrane  is wavelength cos  is angle between tube and sound direction
P is incident sound pressure L is extra distance sound travels (length of tube)

41. Modification to couple vibrations
Connect tympanum to air with horn
Increase sound capture
Pinna extends horn out beyond body
Use light membrane with air behind
Low impedance to match air

42. Amplification Motion of tympanum transferred to smaller oval window
Concentrates pressure at tympanum onto smaller area
Better excites motion of liquid in fluid filled cochlea

43. Analysis of sound vibrations
Peripheral frequency analysis
Place principle analysis
Different frequencies displace different parts of substrate
Tonotopic map
Spatial relationship of nerve cells and frequencies

44. Locust ear Ear on abdomen Thin membrane
PV high frequency mechanoreceptors
Thick membrane
FB for low frequency mechanoreceptors
Windmill, J. F. C. et al. J Exp Biol 2005;208: Measuring tympanal vibrations in the locust S gregaria
Fig. 2. Measuring tympanal vibrations in the locust S. gregaria. (A) Anatomical position of the ear on the abdomen of the locust. TM, tympanal membrane; W, wing; A1, first abdominal segment; A2, second abdominal segment; T3, third thoracic segment. (B) SEM of locust ear. Thin membrane outlined in red, thick membrane outlined in green; PV, insertion point of the pyriform vesicle (high frequency mechanoreceptors, highlighted in blue); FB, insertion point of the folded body (low and mid frequency mechanoreceptors, highlighted in green). (C) Capture of the video image from the laser Doppler vibrometer illustrating the viewing angle of the TM during measurements and the lattice of laser scanning points (N=488 points; scanning mesh size: 70 µm, dot positioning accuracy: ~1 µm). (D) Coherence maps of the tympanal vibrations at 3.3, 6.1, 12.21, kHz. For each scan, coherent data (>85%) could be taken on ~350 data points across the entire surface of the TM. Because only the tympanum moves in a coherent way with sound, coherence drops beyond its edge
Windmill et al 2005

45. Each frequency differentially excites the tympanum
Motion in different locations sensed by different patches of receptors
Frequency = location
Probably more accurate to say frequency is linked to a set of locations
Windmill et al 2005

46. Cochlea has hair cells supported by basilar membrane
Basilar membrane responds to high, med and low freq as move down the cochlea - tonotopic map

47. Frequency response Frequency response differs down membrane
Frequency response differs down membrane
Place sensory cells at different locations to sense different frequencies

48. Organ of Corti
Tectorial membrane
But hair cells are also tuned to different frequencies so there is more to tonotopic map than just resonances of basilar membrane
Hair cells are deflected at location on basilar membrane
Fain Fig 6.18

49. Neuronal firing rate increases with logarithm of sound intensity
Neuronal firing rate (spikes / sec
So if silent room, then might turn on at 20 dB and go up to 60 dB or in loud concert, start at 60 dB and go up to 100 dB.
Sound intensity (dB)
So neuronal firing is linear with sound intensity on dB scale
-the reason we put up with decibels!

50. Neurons adapt to overall sound intensity
Neuronal firing rate (spikes / sec
So if silent room, then might turn on at 20 dB and go up to 60 dB or in loud concert, start at 60 dB and go up to 100 dB.
Sound intensity (dB)
Neuron turns on at 40 dB and response increases linearly up to 80 dB. Neurons also adapt to background noise, determining when they turn on.

51. Comparisons of Ear Designs
How have designs been adapted to animal size and habitat
Insect ears
Fish ears
Terrestrial vertebrate ears

52. Insect ears can be based on subgenual organ
Accessory cell causes deflection of cilia
Neural output to motion
Scolopale cell - supporting cell
Secretes extracellullar membrane
Detect vibrations transmitted from cuticle through accessory cell
Tympanal organs
Johnston’s organ
Scolopale cell is equivalent to cap in other two cell types.
This is also considered a chordotonal organ - senses body position or vibrations for hearing.

53. Water strider
Detects substrate (water) vibrations with subgenual organ located in tibia (legs)
Frequencies Hz
Discriminate ± 1.5 Hz
Evolutionary predecessor of insect ears

54. Johnston’s organ Located in antennae Sense vibrations
May be important in “hearing” mates

55. Sound causes segment 3 to rotate relative to segment 2
Johnston organ
Sound causes segment 3 to rotate relative to segment 2
Responds w/in 1.2 ms
Hear with antennae
Christensen and Corey

56. Some insect ears are based on tympanum connected to air spaces
Locust Cicada
Katydid Cricket
Acoustical coupling of two ears
Pressure differential detectors
Gives them directionality for lower frequencies
Muller’s organ (locust) and auditory capsule (cicada)
contain the sensory cells
When ears are acoustically coupled, they act as pressure differential detector - directionality but at higher frequencies the coupling breaks down and they become pressure detectors Locust - Muller’s organ contains sensory cells
Katydid - ears in tibia of front legs. Connected to tracheal tube which 1) amplifies intensity of sound dB

57. Insect ears are based on tympanum connected to air spaces
Locust Cicada
Katydid Cricket
Katydid - ears in tibia of front legs. Connected to tracheal tube which 1) amplifies intensity of sound dB 2) makes tympanum a pressure differential detector - directionality
Cricket gets sound from 4 places: 1) directly from tympanum, 2) from spiracle on same side body, 3) from spiracle on other side body (35%) and 4) other tympanum (10-20% of direct signal)

58. Cricket call
Frequency 5 kHz with 5 chirps per second

59. Insect accomplishments
Degree of directionality
Detected best for 60 deg in front of animal
Good frequency resolution
If enough sensory cells
May sacrifice resolution to tune ears to narrow species specific frequency
Sensitive above 40 dB SPL
Low sensitivity is result of insects’ small size relative to wavelengths (freq) which most useful in their environment

60. Fish ears Hard to capture sound
Entire body vibrates with incident sound
Fast velocity means long wavelengths
Fast velocity means small temporal differences in sound localization

61. 3 chambers to detect sound along 3 orthogonal axes
Otolith in each chamber which is dense and so inertially slower; stimulates hair cells in response to low frequency vibrations (<200 Hz)

62. Ears of deep sea fish Deng et al 2011 (Dr Popper)

63. Swim bladder can also couple sound to the ears
Converts high pressure, low particle displacement into low pressure, high particle displacement to increase sensitivity
As pressure sensor - no directionality info
Resonances in kHz range so this can extend sound sensitivity above 1 kHz given by otolithic sensor
Swim bladder can have horns (extensions) which are air sacs
Or connections can be small bones

64. Butterfly fish
Webb et al Swim bladder of Chaetodon octofasciatus. A shows X ray picture but not sure why horns don’t show up

65. Improvements from different kinds of swim bladder connections
Example
Increase in sensitivity
Frequency range
Swim bladder touches auditory area
Squirrel fish
20 dB
1 kHz
Fingerlike projection of swim bladder
Soldierfish, herring
Even better
4 kHz
Bones connect swim bladder to ear
Goldfish, minnow, catfish
50 dB
Temporal patterns encode species identify, sex and social function

66. Terrestrial ears
Couple sound through light tympanum through bones to liquid filled tube where hair cells reside
In amphibians, hair cells are embedded in wall of inner ear
Amphibian ear

67. Bull frog ear Amphibian papillae (AP)
Responds to frequencies of Hz
Basilar papillae
Responds to freq of 1-5 kHz
Saccule macula
Responds to Hz

68. Terrestrial ears
Hair cells sandwiched btn tectorial membrane and basillar membrane
Sensitivities up to 150 kHz
Freq sensitivities may be at loss of some time resolution
Higher vertebrate ear

69. Auditory transduction

70. Other ears B) Owl dish shaped face
C) Assymetric placement of ear openings in barn owl
D) Echolocating bat have large pinna to collect certain frequencies
D) Nose leaf of Phyllostomatidae provides a narrow beam of sound going out for echolocation