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HUMAN HEARING AND
NATURE’S APPLICATIONS
Section 10.1 and 10.7
For a prize?
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What does SONAR stand for?
SOund NAvigation and Ranging
Echolocation
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Using echoes to locate an object
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Use a variety of frequencies (40 kHz – 130 kHz)
Dolphins
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Nasal sacs make high-frequency sounds.
Sounds pass through the “melon”
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Oval-shaped sac that is filled with acoustical lipids that focus the sound
waves
Echo is received by a
fat-filled cavity in lower jaw
Only good for ~ 5m - 200m
(High frequency sound)
Vibrations are conducted to
an auditory nerve and are
perceived by dolphin much the
same as sound in humans.
video
Elephants
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Extremely intelligent
Large portion of their brain devoted to hearing.
Large pinnae
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Used mostly for cooling and
threat display
Have hearing receptors
in trunks and feet
Produce sound from
15Hz – 35Hz up to 117dB
Long distances
 video
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Bats
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Of the some 900 species of bats, more than half
rely on echolocation to detect obstacles in flight,
find their way into roosts and forage for food.
Most bats produce echolocation sounds by
contracting their larynx (voice box).
A few species, though, click their tongues.
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sounds are generally emitted through the mouth, but
Horseshoe bats (Rhinolophidae) and Old World
leaf-nosed bats (Hipposideridae) emit their
echolocation calls through their nostrils: there they
have basal fleshy horseshoe or leaf-like structures
that are well-adapted to function as megaphones.
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calls are usually ultrasonic--ranging in frequency
from 20 to 200 kilohertz (kHz)
human hearing normally tops out at around 20 kHz.
In general, echolocation calls are characterized by
their frequency; their intensity in decibels (dB); and
their duration in milliseconds (ms).
Video – what does this sound like?
pitch
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bats produce echolocation calls with both constant
frequencies (CF calls) and varying frequencies that
are frequently modulated (FM calls).
Most bats produce a complicated sequence of calls,
combining CF and FM components.
Although low frequency sound travels further than
high-frequency sound, calls at higher frequencies
give the bats more detailed information--such as
size, range, position, speed and direction of a
prey's flight.
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bats emit calls as low as 50 dB and as high as 120
dB, which is louder than a smoke detector 10
centimeters from your ear.
That's not just loud, but damaging to human hearing.
The Little brown bat (Myotis lucifugus) can emit such
an intense sound.
The good news is that because this call has an
ultrasonic frequency, we are unable to hear it.
Too cool!
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The ears and brain cells in bats are especially tuned to the
frequencies of the sounds they emit and the echoes that result. A
concentration of receptor cells in their inner ear makes bats
extremely sensitive to frequency changes: Some Horseshoe bats can
detect differences as slight as .000l Khz. For bats to listen to the
echoes of their original emissions and not be temporarily deafened
by the intensity of their own calls, the middle ear muscle (called the
stapedius) contracts to separate the three bones there--the malleus,
incus and stapes, or hammer, anvil and stirrup--and reduce the
hearing sensitivity. This contraction occurs about 6 ms before the
larynx muscles (called the crycothyroid) begin to contract. The
middle ear muscle relaxes 2 to 8 ms later. At this point, the ear is
ready to receive the echo of an insect one meter away, which takes
only 6 ms.
Owls
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An Owl's range of audible sounds is not unlike that
of humans, but an Owl's hearing is much more acute
at certain frequencies enabling it to hear even the
slightest movement of their prey in leaves or
undergrowth.
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Some owl species have asymmetrically set ear
openings (i.e. one ear is higher than the other) - in
particular the strictly nocturnal species, such as the
Barn Owl or the Tengmalm's (Boreal) Owl.
These species have a very pronounced facial disc,
which acts like a "radar dish", guiding sounds into
the ear openings. The shape of the disc can be
altered at will, using special facial muscles!
Barn owl
Boreal Owl
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Also, an Owl's bill is pointed downward, increasing
the surface area over which the soundwaves are
collected by the facial disc. In 4 species (Ural,
Great Gray, Boreal/Tengmalm's & Saw-whet), the
ear asymmetry is actually in the temporal parts of
the skull, giving it a "lop-sided" appearance.
Northern Saw-whet Owl
Great gray owl skull
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Owls listen for prey movements through ground cover
such as leaves, foliage, or even snow.
When a noise is heard, the Owl is able to tell its
direction because of the minute time difference in which
the sound is perceived in the left and right ear - for
example, if the sound was to the left of the Owl, the
left ear would hear it before the right ear.
The Owl then turns its head so the sound arrives at both
ears simultaneously - then it knows the prey is right in
front of it.
Owls can detect a left/right time difference of about
0.00003 seconds (30 millionths of a second!)
House Cats
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Excellent hearing (from 55 Hz – 79 kHz)
Large, moveable pinnae
 Amplification
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and directionality of sound.
Make up for poor
vision with their
excellent hearing.
 Seeing
well in the
dark sacrifices
some colour
vision
On the offense?
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hard to believe that animals can in fact use auditory
signals to harm other animals.
The bottlenose dolphin uses echolocation
frequencies that can be over ten times our upper
hearing of 20 kHz. Some high-intensity click sounds
(230 dB) by bottlenose dolphins, beaked whales,
and sperm whales may serve to debilitate prey by
overloading fish lateral lines, ears, or shattering
bony ossicles and other tissue.
10.7 Summary
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Natural phenomena can be explained with reference to the
characteristics and properties of sound waves.
Dolphins, sperm whales, and orca whales use echolocation to
navigate and detect prey in dark, murky waters.
Bats also use echolocation to detect prey.
Elephants produce infrasound waves, which travel partially
through the ground. They can detect these sounds with their
feet and trunks pressed against the ground.
Cats use their large movable pinnae to amplify sound and
to detect the direction from which sounds are coming.