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A hearing aid or deaf aid is an electroacoustic device which is designed to amplify sound for the wearer, usually with the aim of making speech more intelligible, and to correct impaired hearing as measured by audiometry. In the United States, Hearing aids are considered medical devices and are regulated by the Food and Drug Administration (FDA). Ordinary small audio amplifiers or other plain sound reinforcing systems cannot be sold as "hearing aids". Earlier devices, known as ear trumpets or ear horns, were passive funnel-like amplification cones designed to gather sound energy and direct it into the ear canal. Similar devices include the bone anchored hearing aid, and cochlear implant. ==Uses== Hearing aids are incapable of truly correcting a hearing loss; they are an ''aid'' to make sounds more accessible. Two primary issues minimize the effectiveness of hearing aids: * When the primary auditory cortex does not receive regular stimulation, this part of the brain loses cells which process sound. Cell loss increases as the degree of hearing loss increases. * Damage to the hair cells of the inner ear results in sensorineural hearing loss, which affects the ability to discriminate between sounds. This often manifests as a decreased ability to understand speech, and simply amplifying speech (as a hearing aid does) is often insufficient to improve speech perception. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hearing aid」の詳細全文を読む スポンサード リンク
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