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Echolation
Echolation is recognized as a method utilized by a variety of aquatic, nocturnal, and cave-
dwelling zoological subjects to localize objects and perceive the environment by means ofreflection of ultrasonic sounds, where sound pulses are emitted by the auditory system and
reflected from objects in the environment as waves, which may be interpreted by the auditory
system, similar to the visual system.
The process was termed, "echolocation" by Donald Griffin, who pioneered a breakthrough in
studies of the auditory system upon discovering the use of ultrasonic by bats in order to avoid
obstacles, although echolocation used by bats was observed in the early 19th
century by
Lazzaro Spallanzani, an Italian scientist.
The use of echolocation provides for an increase in independence from strict use of the visual
system, aiding in navigation, orientation, and location of prey in poor light or the dark.
Species to use echolocation include bats and dolphins, primarily, but not exclusively, as
birds, rodents, insectivores, Megachiroptera, fish, seals, cetaceans, large aquatic mammals,
the platypus, and blind humans have been found to use echolocation.
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Animal Echolocation
Animal Echolocation makes use of active sonar, using sounds made by an animal. Ranging
is done by measuring the time delay between the animal's own sound emission and anyechoes that return from the environment. The relative intensity of sound received at each ear
provides information about the horizontal angle (azimuth) from which the reflected sound
waves arrive. Unlike some sonar that relies on an extremely narrow beam to localize a target,
animal echolocation relies on multiple receivers. Echolocating animals have two ears
positioned slightly apart. The echoes returning to the two ears arrive at different times and at
different loudness levels, depending on the position of the object generating the echoes. The
time and loudness differences are used by the animals to perceive distance and direction.
With echolocation, the bat or other animal can see not only where it is going but also how big
another animal is, what kind of animal it is, and other features.
[Cacaphony of Dolphins ... Spectrogram of their Clicks,Whistles, and whines]
[Spectrogram of Pipistrellus Bat as it closes in on prey]
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Echolocation in Bats
Bats are also known specifically for their use of echolocation to navigate and catch prey in
the darkness: they are constantly releasing ultrasonic waves during the whole time they areawake, using it to enhance their sight, which exceeds the sight ofhomo sapiens on its own.
By emitting and receiving ultrasonic sound waves, they retain the ability to see further
distances than many other organisms and can derive information which is much more refined.
Bat sonar process: ultrasonic waves are emitted from the bat as cries which then travel and
are reflected back to the bat upon interacting with a moving or non-moving object of varied
density. By measuring the delay in time from the wave emission and the return of the echo,
the bat is able to determine the distance of the object, where amplitude is used as an
indication of the size and shape of the object. With that information, the bat is able to locate
precisely its prey with knowledge of how large or small it is, and thus it is able to hunt for itsprey.
The sound waves emitted may be of varying frequencies, varying by species and individual,
and different sound waves used may collect more refined information. It has also been found
that the production of ultrasonic cries demands from the bat a large amount of energy,
particularly if the bat is flying, which would suggest that the hunt for food is an exhausting
activity. However, it has been found that to bypass the affects of participating in the two
activities at once, bats who use sonar inhale oxygen to use their flight muscles and exhale air
pulses in order for the ultrasonic waves to be transmitted.
Bats possess a mechanism called automatic gain control (AGC), which provides the bat with
the perception of a fixed echo intensity level as it approaches its target: where echoes will
change based on the change in distance and echo strength, contractions of muscles in the
bats middle ear diminishes after ultrasound emission, which produces changes in the bats
hearing and balances the echo changes due to distance. Amplitude would also change as the
bat moves; however, it is believed that the AGC regulates the amplitude as well.
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Human Echolocation
Human echolocation is the ability of humans to detect objects in their environment by
sensing echoes from those objects. This ability is used by some blind people to navigatewithin their environment. They actively create sounds, such as by tapping their canes, lightly
stomping their foot or by making clicking noises with their mouths. It can however also be
fed in to the human nervous system as a new sensory experience. Human echolocation is
similar in principle to active sonar and to the animal echolocation employed by some
animals, including bats and dolphins.
By interpreting the sound waves reflected by nearby objects, a person trained to navigate by
echolocation can accurately identify the location and sometimes size of nearby objects and
not only use this information to steer around obstacles and travel from place to place, but also
detect small movements relative to objects.
However, in the case of human clicking, since humans make sounds with much lower
frequencies and slower rates, such human echolocation can only picture comparatively much
larger objects than other echolocating animals.
To demonstrate the processes of deriving this conclusion, conceived from bat research, see
the timeline below:
1739: Diderot observed that a blind person could perceive presence and distance of objects.
Theories accumulated to explain this detection: skin sensitivity to temp/pressure; pressure on
tympanic membrane (vibrates sound waves in inner ear); magnetism, electricity, "sixth
sense".
1893: Dresslar experiments on detection of echoes reflected from obstacle surfaces:
eliminated different senses of blindfolded subjects and observed. 1st
condition: vision
eliminated. 2nd
: vision, thermal, and facial pressure eliminated by covering exposed skin but
not auditory meatus. Final: hearing eliminated by plugging ears but leaving face exposed,
eyes covered. It was concluded there was the ability to detect due to some auditory
mechanism but others disagreed with the results.
1941: Griffin, Galambos: 1941 gaggedbats to prevent emission of supersonic cries; plugged
ears to prevent echo reception to show the increase in collision frequency.
Cotzin, Dallenbach: after showing importance of hearing, found that in order for the blind to
avoid collisions with a wall, must hear changes in sound pitch with frequency above 10kHz.
(Higher frequencies allow better echo resolution reflected from small targets)
1944: Supa, Cotzin, Dallenbach: discovered stimulation of auditory system (not skin) was
necessary and sufficient to detect objects. When air-waves prevented from impinging on
exposed skin of blind/blindfolded, the subject could still detect obstacles by listening tofootsteps. When hearing was eliminated and skin left exposed, objects could not be detected.
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1947: Worchel, Dallenbach: found partially deaf and blind could not detect obstacles if
hearing was prevented. If skin of external ears covered but auditory meatus exposed,
obstacles could be detected. Therefore, auditory stimulation was the mechanism used to
detect obstacles in blind.
1953: Ammons, Worchel, Dallenbach: blindfolded subjects able to detect obstacles outdoors,revealing that subjects relied on/sought out non-auditory clues like odors and shadows- other
senses enhance obstacle detection
1962: Kellogg: blind subjects presented with two flat disks of same diameter. For each trial: a
pair of targets, where one was at constant distance with the comparison at variable distance.
Targets presented one after another in a pair in rapid succession. Subjects were to generate
any sound desired (acoustic signals: tongue clicks, hisses, whistles, voice, the latter which
was preferred by subject). Target size kept constant as distance changed: subject was to
report larger of targets by listening to echoes reflected off disks. Kellogg observed that
objects closer to observer thought to be larger than standard of same diameter, where objectsfurther away were perceived as smaller.
The blind have an ability to discriminate objects of different size, with up to 100% accuracy,
the smaller object of two different sized objects (placed at same distance). Performance
decreased as distance increased.
1965: Rice: percent correct detection was proportional to size and distance of object from
observer. At greater distance, objects needed to be larger to be detected. As object was placed
further, sound intensity of echo lowered and object detection became more difficult. As
object size increased, detection improved. Therefore sound intensity of echoes (size and
distance manipulated) affected ability to detect.
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Ultracane
The mobility aid system works on the simple principle of reflection of sound waves from the
obstacle or an object. For this set up, the system has a simple battery operated circuit, actingas an oscillator producing the required 40 KHz frequency for the operation of the ultrasound
generator. The ultrasound generator generates sound waves, which are higher in frequency
than the human audible range [ultrasound waves]. Thus generated, sound waves burst open
from an optimal point in the walking stick so that the ultrasound could cover the maximum
distance. The ultrasound generator is fixed inside a non-foldable walking stick and only the
transmitter is exposed to the outer world.
The transmitted sound waves spread and are transported widely in the area around. They
travel free in the free surface. During this time, the receiver senses lower than the frequency
threshold set by the user. In case of an obstacle ahead, the sound wave gets reflected from the
obstacle or objects and reflects back to transmitters direction.
In the walking stick, the receiver or the sensor is kept very close to the
transmitter. The sensor senses the sound waves and if the threshold is
exceeded, it amplifies that signal given to the alarm circuit depending
on the closeness of the cane to the object. Closer the object higher is the
intensity of the alarm.
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The alarm can be triggered using different techniques:
1. Beep Alert
A very simple electronic circuit is used for this purpose. The number of beeps for a specifictime period varies directly with the intensity of the sensed signal. If the object is closer, the
number of beeps is higher.
Advantages of beep alert:
Cost effective
Audible alert so easily sensible by the user, a very effective alert system
2. Vibrator Alert
Vibrator alert is employed for users who are both blind and deaf. It not only provides the user
with the comfort of a noise free alert system, but also facilitates use in a noisy environment.
The UltraCanes handle emits ultrasonic waves that bounce off objects as far as four meters
away and send signals to the user through two vibrating buttons on the handle. The strength
of the buttons pulses indicates the direction, height and distance of the objects. The same
part of the brain that a bat uses to orient its movementsthe superior colliculushelps a
human process the buttons pulses to build a spatial map in her minds eye of how the
obstacles are arranged, allowing her to walk more quickly and confidently than she could
with an ordinary white cane.
3. Speech Processor Chip
Speech processor chip can be incorporated with
the current Ultrasound system and recorded
voice alerts can be given to the users. It can be
very instrumental in cases where the direction
of the alert has to be provided. However, one
major drawback of this system is that the user
has to wear an earphone, which interrupts the
sounds from the surrounding environment. Thiswould actually worsen the mobility of the
visually challenged.
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Alternative Aids or Future Advancements
Development of an ultrasound head band for alerting the patient about theobstacles ahead
Smart goggles
Advanced systems based on radar principles
Smart wheel chair
Other Uses of Ultrasound or Similar Principles
SONAR: (SOund Navigation And Ranging)Warfare Civilian Scientific
Anti-submarine warfare Fisheries Biomass estimation
Torpedoes Echo sounding Wave measurement
Mines Net location Water velocity measurement
Mine countermeasures Ship velocity measurement Bottom type assessment
Submarine navigation Remotely Operated Vehicles
(ROV) and Unmanned
Underwater Vehicles (UUV)
Bottom topography
measurement
Aircraft Vehicle location Sub-bottom profiling
Underwater communications Synthetic aperture sonarOcean surveillance Parametric sonar
Underwater security
Hand-held sonar
Intercept sonar
RADAR: (RAdio Detection And Ranging)To identify the range, altitude, direction,
or speed of both moving and fixed objects such as aircraft, ships, spacecraft, guided
missiles, motor vehicles, weather formations, and terrain.
SONOGRAPHY: Medical Imaging: A-scan, B-scan, M-scan, Colour Doppler, etc.
Short Conclusion
Most common solution of our huge problems is lying in nature surrounding us. All
we need to explore ourselves to get it. We cant get human vision, and then at least
try our technology to provide sound as sight. We cant bring evolution at instance
but we can try to make out necessary adjustment to evolve....
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