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A disruption in the normal hearing process that may occur in the outer, middle, or inner ear, which prevents sound waves from being converted to electrical signals and nerve impulses from being transmitted to the brain to be interpreted. Included are conductive hearing loss that results from abnormalities of the external ear and/or the ossicles of the middle ear; sensorineural hearing loss that results from malfunction of inner ear structures (i.e., cochlea); and central auditory dysfunction that results from damage or dysfunction at the level of the eighth cranial nerve, auditory brain stem, or cerebral cortex. Hearing loss may be present at birth (congenital) or become evident later in life (acquired); and may or may not preclude the normal development of language. The severity of hearing loss is measured in decibles (dB). The threshold or 0 dB mark for each frequency refers to the level at which typical young adults perceive a tone burst 50% of the time. Hearing is considered normal if an individual's thresholds are within 15 dB of normal thresholds. Severity of hearing loss is graded as mild (26-40 dB), moderate (41-55 dB), moderately severe (56-70 dB), severe (71-90 dB) and profound (90 dB).