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A system of object detection, location, identification, and ranging by means of echolocation, the emission of sound or ultrasound and the analysis of returning echoes. It has evolved independently in two groups of bats and also in dolphins, whales, oilbirds (Steatornis caripensis) of South America and Trinidad, and cave swiftlets of the Asian genus Collacalia, and is also used in a primitive form and to a small extent by shrews, rats, seals, and blind human beings (see facial vision). In its most sophisticated form as used by dolphins, whales, and some bats, the time delay of an echo provides information about the distance of the target object; transient disparities, phase delays, and sonic shadows enable the target's direction to be pinpointed; the amplitude of an echo indicates the target's overall size; the amplitudes of the echo's component frequencies provide clues as to the sizes of the target's features; and the Doppler effect indicates whether the target is coming closer or moving away. The bottlenose dolphin (Tursiops truncatus) can detect a steel ball the size of a walnut under water at a range of 64 metres (210 feet). [From Greek bios life + English sonar an acronym for so(und) na(vigation and) r(anging)]

Subjects: Psychology.

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