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Hearing (or audition) is one of the traditional five senses, and refers to the ability to detect the vibrations of particles against the ear drum. 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]

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 and electrocochleography (EchoG). Technical advances in these tests have allowed hearing screening for infants to become widespread.

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]

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 in order to communicate with each other and hearing in these species is particularly important for survival and reproduction. In species using 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. 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.

1. ^ Kung C., "A possible unifying principle for mechanosensation," Nature, 436(7051):647–54, 2005 Aug 4.
2. ^ (Shupak A. Sharoni Z. Yanir Y. Keynan Y. Alfie Y. Halpern P. Underwater hearing and sound localization with and without an air interface. [Journal Article] Otology & Neurotology. 26(1):127-30, 2005 Jan.)

• Audiograms in mammals
• Audiometry
• Auditory illusion
• Auditory brainstem response (ABR) test
• Auditory scene analysis
• Auditory system
• Cochlear implant
• Equal-loudness contour
• Hearing impairment
• Missing fundamental
• Music
• Music and the brain
• Presbycusis
• Tinnitus

• Egopont hearing range test