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Post-lingual hearing impairments are far more common than pre-lingual impairments. Typically, hearing loss is gradual, and often detected by family and friends of the people so affected long before the patients themselves will acknowledge the disability.
In cases where the causes are environmental, the treatment is to eliminate or reduce these causes first of all, and then to fit patients with a hearing aid, especially if they are elderly. When the loss is due to heredity, total deafness is often the end result. On the one hand, persons suffering from gradual deterioration of their hearing are fortunate in that they have learned to speak. On the other, they often suffer from social isolation, because they can no longer understand their friends, who cannot communicate effectively with them. Ultimately, unless the affected person becomes skilled in speech-reading ( lip-reading ), or receives a cochlear implant, he/she will depend on sign language for communication.
In some cases, the loss is extremely sudden. Most often, the cause is unknown. Sometimes, it can be traced to specific diseases, such as meningitis, or to ototoxic medications, such as Gentamicin. In both cases, the final degree of loss varies. Some suffer only partial loss, while others become profoundly deaf. In the former case, hearing aids can be used with varying degrees of success, depending on the exact nature of the loss. In the latter, ultimately the affected person will depend on speech-reading and/or sign language for communication.
People who are hard-of-hearing have moderate amounts of hearing loss but not enough to be considered deaf.
The phrase hard-of-hearing, normally used as an adjective or adverb, can also be used as a noun, referring to people with hearing impairment as the hard-of-hearing.
Hearing impaired persons with partial loss of hearing may find that the quality of their hearing varies from day to day, or from one situation to another. They will also, to a greater or lesser extent depend on both hearing-aids and lip-reading, similarly to more severely disabled people. They may perhaps not always be aware of it, but they do admit to it being important to see the speaker's face in conversation.
Many people with hearing loss have better hearing in the lower frequency ranges (low tones), and cannot hear as well or at all in the higher frequencies. Some people may merely find it difficult to differentiate between words that begin with consonantal sounds such as the fricatives or sibilants s, z, or th, or the plosives d, t, b, or p. They may be unable to hear thin, high-pitched or metallic noises, such as birds chirping or singing, clocks ticking, etc. Often, they are able to hear and understand men's voices better than women's.
Others will find their condition so much worse if circumstances in their immediate environment affect the way they are able to use their hearing-aids, or prevent them from employing their lip-reading skills. A room with a high ceiling and a lot of reverberation will affect the sound of a speaker's voice adversely. The position of the listener, too, sitting at a right angle to the speaker at a long seminar table, thus being able to hear only with one, maybe the ineffectual ear, can make a difference. Difficulties can also arise for the listener trying to lip-read, if the speaker is sitting with his back against the light-source and is in this way obscuring his face.
The speaker's accent; the topic under discussion, possibly with many unfamiliar words; the softness of his voice; possibly his having a speech impediment; a habit of holding a hand in front of his mouth or turning his face away at times: all these tendencies cause problems to the hard-of-hearing, especially when they have to rely on lip-reading. The rustling of papers, and notebook pages being turned are precisely the noises that will be the first thing hearing-aids pick up.