Hearing (sense)
Hearing, or
audition, is one of the traditional five
senses and refers to the ability to detect
sound.
Hearing is performed by the auditory system in humans and other vertebrates.
Sound is detected by the
ear, and transduced into nerve impulses that are perceived by the
brain. Many animals use sound in order to communicate with each other, hearing in those species that communicate with sound is particularly important for survival and reproduction.
All sounds are not normally audible to animals. Each species has a range of normal hearing for both loudness (amplitude) and pitch (frequency). Human hearing is most sensitive in the so-called "speech frequencies", which range from about 500 to 2000 hz. In animals that use sound as a primary means of communication, hearing is typically most acute for the range of pitches produced in calls and speech. A common rule of thumb used to describe human sensitivity to pitch is
frequency of 20
Hz to 20
kHz. The normal human range of hearing 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. Frequencies capable of being heard by humans are called
audio or referred to as
sonic. Frequencies higher than audio are referred to as
ultrasonic, while frequencies below audio are referred to as
infrasonic.
Human beings develop spoken language within the first few years of life, and hearing impairment can not only prevent the ability to talk but also the ability to understand the spoken word. By the time it is apparent that a severely hearing impaired (deaf) child has a hearing deficit, problems with communication may have already caused issues within the family and hindered social skills, unless the child is part of a Deaf community where sign language is used instead of spoken language (see
Deaf Culture). In many developed countries, hearing is evaluated during the newborn period in an effort to prevent the inadvertant isolation of a deaf child in a hearing family.(Morton CC. Nance WE. Newborn hearing screening--a silent revolution. [Review] [47 refs] [Journal Article. Review] New England Journal of Medicine. 354(20):2151-64, 2006 May 18.) Most evidence points to early identification of hearing impairment as key if a child with very insensitive hearing is to learn spoken language.
Although sign language is a full means of communication, literacy depends on understanding spoken language. In the great majority of written language, the sound of the word is coded in symbols. Although an individual who hears and learns to speak and read will retain the ability to read even if hearing becomes too impaired to hear voices, a person who never heard well enough to learn to speak rarely is able to read proficiently.
Some organisms are able to hear ultrasound and/or infrasound. 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 there is evidence that
whales and
elephants may use it for communication. See
sound for hearing ranges of various organisms.
Hearing can be measured by behavioral tests using an
audiometer. Electrophysiologic tests of hearing can provide accurate measurements of hearing thresholds even in unconscious subjects.
Arthur Reber says, 'Explaining hearing adequately has proven a singularly difficult task. One would almost ensure oneself a
Nobel prize by presenting a theory explaining satisfactorily no more than the perception of
pitch and
loudness.' (A. S. & E. S. Reber,
The Penguin Dictionary of Psychology (3rd Edn., 2001))
Humans are able to hear a variety of sound frequencies, from 20Hz to 20kHz. Humans can hear the direction of the source of a sound, sometimes with surprising accuracy. Two mechanisms are known to be used.
* Bushy neurons can resolve time differences as small as the time it takes sound to pass one ear and reach the other (10 milliseconds).
* For high frequencies, frequencies with a wavelength shorter than the listener's head, more sound reaches the nearer ear.
Neither of these mechanisms work as well in water, in which the speed of sound is faster than in air.
The arrival time of a sound to a particular ear is given greater weight when localizing than relative intensity, according to an observation known as the
Law of the First Wavefront.
*
Auditory illusion*
Auditory system*
Hearing impairment*
Missing fundamental*
Music*
Music and the brain*
Tinnitus*
Auditory Brainstem Response (ABR) Test
*
Sensaura white papers on human hearing and emulating hearing in 3D
*
Sensaura tutorial on 3D sound*
"Protect Your - Hearing!", from
Awake! magazine (May 22, 2002)
