Lecture #25 Chapter 25 : Autocommunication 5/5/11 Key dates Final exam questions will be posted Friday by noon Wiki projects are due Tuesday, May 10th at midnight Last class on Tuesday Final exam Thursday, May 12th 8
am Today Echolocation basics Echolocation in bats Open-site foragers Gleaners Hawkers and fishers Echolocation in cetaceans Autocommunication
Echolocation = biosonar Emit pulses of sound Electrolocation Determine environmental information about nearby objects What is its size and shape? What is it doing? Where is it now and where might it be going? Autocommunication Not technically communication
Shaped by same design factors such as??? Autocommunication Not technically communication Shaped by same design factors Shape signals to adjust for - Efficient emission - Propagation and distortion - Reception Why is environmental signaling
simple or absent much of time? Do senders rarely reap benefits of communicating more complex information (benefits go to receivers)? OR Is it too difficult and expensive to encode and extract information? Autocommunication should represent perfect communication
Sender and receiver are the same individual - NO CONFLICT Receiver should be ideal receiver extract as much information as possible Sender should pack as much information in as possible Autocommunication should be perfect test case So are autocommunication signals
more complex than those between individuals? (no game) Or are they just as simple because it is too difficult to encode and extract info? Echolocation Simple echolocation Oilbird Lesser tenrec
Shrew More sophisticated echolocation Echolocation information Environmental information: Object location (range, angle) Object identity (shape, texture composition) Relative velocity and trajectory
May be trade offs btn object properties Accuracy about one may require uncertainty in another Detecting targets at distance Outgoing signal must be loud enough to produce echo that is above ambient noise Signal must be emitted enough of time that sound beam will strike target
Best if work at single frequency All energy at that frequency Tune receiver to that frequency Echo intensity 1/distance4 d Signal 1/distance 2
Echo 1/distance2 Scattering summary Fig 2.6 Other factors Want frequency that can emit with highest intensity Maximum reflection when wavelength < object For 1cm insect, minimum freq is 34
kHz For 10 cm fish, minimum freq is 3 kHz Echolocation signals Echolocation signals - optimal frequency is balance of production and propagation Pulse duration Send out pulse of sound
Need to leave silence to hear echo Time between pulses (trep) = 1 / frequency Duty cycle = fraction of time are calling per pulse = tpulse / trep tpulse trep Time for echo to return Sound velocity = distance / time Return time = distance / velocity
Distance = Velocity * time Distance to object 2 *Object_ distance Echo_ return_ time _ t = sound_ velocity Time for echo to return Signal Echo
techo 2 * object _ distance techo = sound_ velocity Minimum distance probed determined by pulse width Signal tpulse Echo
techo = tpulse Have to wait for outgoing pulse to end before can hear echo pulse_ width* sound_ velocity Min _ distance= 2 =tpulse*170m / s
Minimum distance probed determined by pulse width Signal tpulse Echo techo = tpulse pulse_ width* sound_ velocity
Min _ distance= 2 =tpulse*170m / s Pulse width Distance (m) 0.1 s 17 m
0.01 s 1.7 m 0.001 s 0.17 m Maximum distance probed determined by pulse repetition Signal tpulse
techo = trep Echo Max_ distance = =trep *170m / s Want to receive echo before next pulse begins repetition
_ time * sound_ velocity 2 Maximum distance probed determined by pulse repetition Signal tpulse techo = trep rep_ time * sound_ velocity Max_ distance= 2
=trep *170m / s Echo Freq (Hz) Pulse rep Distanc e
20 0.05 8.5 m 100 0.01 1.7
500 0.002 0.34 Determining target distance Can use echo amplitude Also affected by size and shape of target Can use delay time, techo
Possible that moth only reflect sound when its wings are perpendicular to sound (top and bottom of flap) So only get part of pulse returned If label pulse with frequency, will know which part of pulse is reflected Uncertainties Constant frequency pulse has errors tactual
tmeasured Frequency modulation is more accurate Can compare correlated part of the pulse tactual tmeasured Can decrease
range error from 2.7 to 0.16 cm #2 Doppler demonstration http://www.walter-fendt.de/ph14e/dopplereff.htm Doppler shift Perceived frequency depends on
relative velocity of predator and prey v fobs = fsource vvrel If moving towards, frequency is higher (minus sign) If moving away, frequency is lower (plus sign)
Doppler shifts As bat flies towards moth, echo will be doppler shifted higher Also will arrive sooner than if bat is stationary Can linearly modulate emitted pulse Frequency Period Inver
fre Determining target angle If focus outgoing beam to narrow angle, then know at what target angle get a response High resolution May miss insect Angle may vary with frequency Can also use directional sensitivity of ears
Arrival time delay Emitted beam has angular variation Compensate with angular response of ears!! Emitted beam Ear sensitivity Combination
Determining target properties Distinguish echoes from background (clutter) and target prey Echo amplitude related to target size -- if also know target range (time delay) All aerial targets will reflect No info on what target is made of Most aquatic targets will absorb and may resonate - can use to discriminate what target is made of Determining target velocity and
trajectory Hard to do with frequency modulated pulse Which outgoing frequency matches which incoming frequency?? Using constant frequency signals, can get better estimate of Doppler shifts Get more cycles of sound on target Tradeoff
Frequency modulation Best for estimating range Constant frequency Best for estimating velocity Tough to estimate both range and velocity at same time Decreased error for one increases error for other Animals must choose which to optimize
Echolocation in bats 800 species of bats Megachiroptera Eat fruit, nector or flowers Rely on nocturnal vision (one rudimentary echolocator) Microchiroptera Feed on insects, small verts, blood or fruit/flowers Use echolocation to forage and navigate Open-site foragers : insectivores
Not much clutter to worry about Emit broad beam of sound through mouth (60-90 deg) Loud intensities 100-120 dB SPL As intense as can be w/o collapse blood vessels Three phases of foraging Search Approach Buzz
Decreases pulse width as get closer to target Always stay below echo overlap pulse width When very close, stop echolocating (4-10 cm) Open-site foragers Range Pipistrelle is small bat Use 30-50 kHz to search Can detect prey > 0.2 mm
Maximum range 1.5-2 m Larger bats use lower frequencies Either to find larger prey Or to find prey at larger distance since not as agile Higher frequency is used at shorter range, requires shorter pulse duration Bats are pretty good at this
Time to catch an insect = 0.5-1 s Catch insect every 4 s Capture efficiency = 30-40% for moths = 60-70% for mosquitos Bat - Gleaners Forage from close to surfaces Foliage, barns Lots of clutter from larger
reflecting surface To prevent being overwhelmed use low sound intensity Whispering bats Narrow beam emitted from nose Insectivorous bats Mouth emission Frugivore Nose emission
Predators Nose emission Predators Nose emission Spiders, lizards Fishing Vampire
hawks insects doves, parro gleans insect Detect moving target against fixed background Need to determine angle of moving target Gleaners have high angular accuracy 1.5-2
Can also perceive fluttering motion in reflected spectrum Can also detect sounds from prey and odors Hawkers and fishers Hang in one location scanning for prey and then fly in to capture Patrol close to vegetation and capture moving insects Fishers detect disturbance on
water surface Need to then predict where fish will be when go to catch it (sonar does not enter water) Fishing bats and finding water Hawking by Rhinolophus Use high duty cycle constant freq pulses with FM
sweeps on end Use very high freq so can detect small targets Doppler shifted echoes from prey Cochlea has hair cells supported by basilar membrane
Basilar membrane responds to high, med and low freq as move down the cochlea - tonotopic map CF bat ears Normal mammalian cochlea has tonotopic map 100 90 80
70 60 50 40 30 20
10 CF bat cochlea has a fovea Region where tonotopic map is expanded 90 80 70
68 66 64 62 60 50
4 Bats are close to ideal receivers Design ideal signals FM sweeps which are Doppler-tolerant Likely use comparison of phase shifts in echoes vs emitted calls to further improve ranging (cross correlation) Gives minimal error possible 0.007 mm May help with target identification
Why is environmental signaling simple or absent much of time? Do senders rarely reap benefits of communicating more complex information (benefits go to Bats use receivers)? OR most complex signals
possible Is it too difficult and expensive to encode and extract information? Echolocation in cetaceans Predatory species echolocate Toothed whales Porpoises Challenges of aquatic habitat Velocity 4.4x greater; Wavelengths
4.4x longer Need higher frequencies for same sized target (vs air) But since larger animals, targets are larger so its a wash Other constraints Faster sound velocities require shorter pulses to prevent pulse - echo overlap 0.05-0.1 ms This is even shorter than needed so dont
have to shorten as get closer to an object as bats do Low attenuation so good signal propagation Dolphin can detect 2 cm target at 73m Bat needs to be 2-4 m to detect it How do cetaceans create pulses? Porpoise emits
through head and detects through jaw Porpoise pulse and power spectrum Cetacean pulse production Sperm whale breathes through left nostril and makes pulses with right nostril Conclusion
Both bats and cetaceans are close to ideal receivers So rest of animals could send and extract more information than they do Likely conflicts of interest Within bats, they do not share their environmental info with other bats Have own personal frequencies One exception to all of this Humans
We share all kinds of environmental information (and other information) with each other Perhaps we will find other animals do better than we think: parrots, corvids, elephants, higher primates and cetaceans Congratulations!! I cant believe we read the WHOLE book There is still more to learn about
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