A hearing impairment exists when an individual is not sensitive to the sounds normally heard by its kind. In human beings, the term hearing impairment is usually reserved for people who have relative insensitivity to sound in the speech frequencies.
Hearing loss can be inherited.
Both dominant and recessive genes exist which can cause mild to profound impairment. If a family has a dominant gene for deafness it will persist across generations because it will manifest itself in the offspring even if it is inherited from only one parent.
People who are hard of hearing have varying amounts of hearing loss but usually not enough to be considered deaf. Many people who are deaf consider spoken language their primary language and consider themselves "hard of hearing".
People with unilateral hearing loss (single sided deafness/SSD) can hear normally in one ear, but have trouble hearing out of the other ear. Problems with this type of deficit is inability to localize sounds.
Those who lose their hearing later in life, such as in late adolescence or adulthood, face their own challenges. For example, they must adjust to living with the adaptations that make it possible for them to live independently. They may have to adapt to using hearing aids or a cochlear implant, develop speech-reading skills, and/or learn sign language.
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