Hearing (sense)

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Hearing (or audition) is one of the traditional five senses. It is the ability to perceive sound by detecting vibrations via an organ such as the ear. The inability to hear is called deafness.

In humans and other vertebrates, hearing is performed primarily by the auditory system: vibrations are detected by the ear and transduced into nerve impulses that are perceived by the brain. Like touch, audition requires sensitivity to the movement of molecules in the world outside the organism. Both hearing and touch are types of mechanosensation.[1]

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[edit] Hearing tests

Main article: Hearing test

Hearing can be measured by behavioral tests using an audiometer. Electrophysiological tests of hearing can provide accurate measurements of hearing thresholds even in unconscious subjects. Such tests include auditory brainstem evoked potentials (ABR), otoacoustic emissions (OAE) and electrocochleography (EchoG). Technical advances in these tests have allowed hearing screening for infants to become widespread.

[edit] Hearing underwater

Hearing threshold and the ability to localize sound sources are reduced underwater, in which the speed of sound is faster than in air. Underwater hearing is by bone conduction, and localization of sound appears to depend on differences in amplitude detected by bone conduction.[2]

[edit] Hearing in animals

Not all sounds are normally audible to all animals. Each species has a range of normal hearing for both loudness (amplitude) and pitch (frequency). Many animals use sound to communicate with each other, and hearing in these species is particularly important for survival and reproduction. In species that use sound as a primary means of communication, hearing is typically most acute for the range of pitches produced in calls and speech.

Frequencies capable of being heard by humans are called audio or sonic. The range is typically considered to be between 15Hz and 20,000Hz.[3] Frequencies higher than audio are referred to as ultrasonic, while frequencies below audio are referred to as infrasonic. Some bats use ultrasound for echo location while in flight. Dogs are able to hear ultrasound, which is the principle of 'silent' dog whistles. Snakes sense infrasound through their bellies, and whales, giraffes and elephants use it for communication.

[edit] References

  1. ^ Kung C. (2005 Aug 4). "A possible unifying principle for mechanosensation". Nature 436 (7051): 647–654. doi:10.1038/nature03896. 
  2. ^ Shupak A. Sharoni Z. Yanir Y. Keynan Y. Alfie Y. Halpern P. (2005 Jan.). "Underwater Hearing and Sound Localization with and without an Air Interface". Otology & Neurotology 26 (1): 127–130. doi:10.1097/00129492-200501000-00023. 
  3. ^ Frequency Range of Human Hearing. The Physics Factbook.

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