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

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

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

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

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

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

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.

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

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

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

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

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.

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.

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

Best terrestrial frequencies?

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

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

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

0.5 - 5 kHz is where noise is lowest

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

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

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

Ideal receiver What does an ideal receiver want to detect?

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

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

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

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

Sound sensing hairs arista Male mosquito Drosophila arista http://www.entomology.umn.edu/museum/links/coursefiles/Brachycera%20characters.html Male mosquito antennae http://www.flickr.com/photos/sweety1/5266126094/ Spider trichobothria: http://www.findaspider.org.au/info/spiderNS.htm Male mosquito

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)

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

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

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

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

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

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

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

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 0.006 msec time differences.

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

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)

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)

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

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

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

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;208:157-168 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, 22.76 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

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

Cochlea has hair cells supported by basilar membrane http://www.pc.rhul.ac.uk/staff/J.Zanker/PS1061/L5/inner_ear.gif Basilar membrane responds to high, med and low freq as move down the cochlea - tonotopic map

Frequency response Frequency response differs down membrane http://www.blackwellpublishing.com/matthews/ear.html Frequency response differs down membrane Place sensory cells at different locations to sense different frequencies

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

Neuronal firing rate increases with logarithm of sound intensity Neuronal firing rate (spikes / sec http://www.deafnessresearch.org.uk/4391/how-we-hear/the-whisper-and-the-siren.html 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!

Neurons adapt to overall sound intensity Neuronal firing rate (spikes / sec http://www.deafnessresearch.org.uk/4391/how-we-hear/the-whisper-and-the-siren.html 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.

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

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.

Water strider Detects substrate (water) vibrations with subgenual organ located in tibia (legs) Frequencies 25-100 Hz Discriminate ± 1.5 Hz Evolutionary predecessor of insect ears

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

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

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 10-30 dB

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 10-30 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)

Cricket call Frequency 5 kHz with 5 chirps per second

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

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

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)

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

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

Butterfly fish Webb et al 2006 Swim bladder of Chaetodon octofasciatus. A shows X ray picture but not sure why horns don’t show up

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

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

Bull frog ear Amphibian papillae (AP) Responds to frequencies of 100-1000 Hz Basilar papillae Responds to freq of 1-5 kHz Saccule macula Responds to 20-100 Hz

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

Auditory transduction http://www.youtube.com/watch?v=PeTriGTENoc&feature=related

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