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The sense or perception of sound. The normal human ear can detect sounds with frequencies ranging from about 20 Hz to 20,000 Hz but is most sensitive to sounds in the 1500-Hz to 3000-Hz frequency range, which is the range most often used in speech. Hearing deficits occur when sound waves are not conducted properly to the cochlea, when lesions interrupt the workings of the cochlear nerve, or when central nervous system pathways involved in the processing of auditory stimuli are injured.
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Hearing acuity can be determined by measuring the distance at which a person can hear a certain sound, such as a water tick, by using audiometers, and by bone conduction. In audiometers, electrically produced sounds are conveyed by wires to a receiver applied to the subject's ear. Intensity and pitch of sound can be altered and are indicated on the dials. Results are plotted on a graph known as an audiogram. In bone conduction tests, a device such as a tuning fork or an apparatus that converts an electric current into mechanical vibrations is applied to the skull. This is of value in distinguishing between perceptive and conductive deafness. Conductive hearing loss may be diagnosed with the Weber test. Having the patient hum produces no difference in the sound heard if hearing is normal. The sound is perceived as louder in the ear with conductive hearing loss.

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