The Sonar
In order to understand how sound is utilized by humans and animals we must know that sound waves can be deviated and reflected. If we recall the compression and the expansion experienced by sound in an alternative way when passes through any element, whether air or water, we are prepared to incorporate a new concept: wave length. The distance between a compression and the next one, this distance is what we call wave length. The higher the frequency, the lower the wave length will be.
As we have learned to know the speed of sound in different materials, by knowing the frequency of sound, we can calculate the wave length.
A big object, when compared to the wave length of a sound will reflect a good portion of that sound. These reflections are called echo. The sounds surround the objects that are small in comparison to the wave length. The fact that objects reflect sounds have been used by men in navigation to locate icebergs or explore the bottom; in commercial fishing to find large banks of fish; and in military operations to determine the position of the submarines.
We know that materials of different densities reflect sound; therefore, in the ocean, the sound bounces against the surface, the bottom and the masses of water of different temperatures, besides animals and plants. The layers of water with different temperatures divert the sound waves that are not reflected. In this way, a sound wave traveling the ocean expands, it is absorbed, changes direction, is reflected and then scatters. The higher the frequency of the sound, the larger the effect will be. Because of that, the majority of far reach echo based sounding lines used by ships operate at a frequency below 5.000 Hz. To detect small objects at much less distance, sonars operate at a frequency which evades the human ear, in other words, above 20.000 Hz.
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For each human invention, there is an equivalent system in nature widely surpassing human’s in efficiency and possibilities. One of them is the animal sonar or echolocation. To obtain information about the environment, dolphins emit sounds which frequency varies below 2.000 and above 100.000 Hz.
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We can perceive those audible to us, as a series of pounds that may appear as individual sounds or like a succession of sounds linked between them.
The dolphins and other members of the suborder of odontoceti, or toothed cetaceans, may determine not just the distance and the course, but the size, the shape, the texture and the density of the objects. Besides, they may also receive more information than we by the simple fact of altering the tone of one of the pounds inside the succession, and since each pound that bounces is different, they may receive a different message. In this way, a single succession of echoes produces a complex mental image of an object.
There are at least four types of information in the echo: the direction from where it comes, the change of frequency, the amplitude of the sound and the time passed between the emission and the return.
While exploring, the dolphin determines the direction followed by the returning echoes, and in this way, the orientation of the object to examine. Changes in frequency speak about its size and shape. The amplitude of sound and the time passed give signals about distance.
Just recently we have begun to understand how these pounds are produced and emitted and the way dolphin perceives the echo: The emission of pounds is originated inside the dolphin’s head. Sounds are produced even when under water, with any loss of air, which suggests that it is recycled inside its respiratory system.
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Both sides of the dolphin’s head and its inferior jaw, with oily fat, are the areas receiving the echo. The protuberance on its forehead is, probably, the place where echolocation pounds are originated.
When a dolphin travels, it moves its head slowly from one side to the other, up and down. This movement is a kind of global scanning that allows the dolphin to see a broader path before it.
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With the use of the sonar, a dolphin with covered eyes may recover a ring.
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But if interested in a small objective, as for example a fish in the middle of dark water, head’s exploratory movements become fast and spasmodic: Low frequencies are far reach but non-directional, high frequency pounds are useful for short reach explorations but higher definition is obtained.
Different from high frequency sound, it is probable that low frequency vibrations are received first by the internal ear. In order to receive and interpret all these echoes, dolphin’s brain possesses a much bigger hearing lobe than ours.
Of course, there is no way to know what is the dolphin hearing. We are unable to imagine how shape and distance of the objects are heard. Dolphin’s system precision is surprising and provides much more information to the dolphin than what human may obtain from the sonar. For example, “Dolly”, is a dolphin trained by the U.S. Navy. It is capable to pick three coins thrown at the same time in three different directions; Dolly picks the first when still sinking, and find the second and the third from the sediments, in just few seconds later, despite a very poor visibility.
Language is the communication of thoughts and feelings. Humans are the only beings in the animal kingdom that are capable of communicating through the use of well defined oral specific patterns, as well as through the use of written transcriptions. The question is: are there other animals besides humans that have a language, according to what we understand as such?.
