Hearing is one of the traditional five senses, and refers to the ability to detect sound. The sense of hearing is sound perception and results from tiny hair fibres in the inner ear detecting the motion of a membrane which vibrates in response to changes in the pressure exerted by atmospheric particles. Basically, sound is detected by the ear and transduced into nerve impulses that are perceived by the brain as "sounds".



The visible portion of the outer ear in humans is called the auricle or the pinna. It is a convoluted cup that arises from the opening of the ear canal on either side of the head. The auricle helps direct sound to the ear canal. Both the auricle and the ear canal amplify and guide sound waves to the tympanic membrane or eardrum. In humans, amplification of sound ranges from 5 to 20 dB for frequencies within the speech range (about 1.5-7 kHz). Since the shape and length of the human external ear preferentially amplifies sound in the speech frequencies, the external ear also improves signal to noise ratio for speech sounds.

The eardrum is stretched across the front of a bony air-filled cavity called the middle ear. Just as the tympanic membrane is like a drum head, the middle ear cavity is like a drum body. Much of the middle ear's function in hearing has to do with processing sound waves in air surrounding the body into the vibrations of fluid within the cochlea of the inner ear. Sound waves move the tympanic membrane, which moves the ossicles, which move the fluid of the cochlea.

The cochlea is a snail shaped fluid-filled chamber, divided along almost its entire length by a membranous partition. The cochlea propagates mechanical signals from the middle ear as waves in fluid and membranes, and then transduces them to nerve impulses which are transmitted to the brain. It is responsible for the sensations of balance and motion.

Humans can generally hear sounds with frequencies between 20 Hz and 20 kHz. Human hearing is able to discriminate small differences in loudness (intensity) and pitch (frequency) over that large range of audible sound. This healthy human range of frequency detection varies significantly with age, occupational hearing damage, and gender; some individuals are able to hear pitches up to 22 kHz and perhaps beyond, while others are limited to about 16 kHz. The ability of most adults to hear sounds above about 8 kHz begins to deteriorate in early middle age.