Many people have partial or complete loss of hearing, a condition known as deafness. There are many causes of deafness. Deafness that is congenital or from early infancy often interferes with the ability to learn spoken language, although signed language is not affected. Deafness that comes later in life usually does not result in poor speech, but may induce the deaf person to become isolated, affecting mental wellbeing. One out of three persons over the age of 65 experiences hearing loss as a part of ageing.
Sounds become muffled, causing the listener to ask people to speak louder.
The hearing-impaired may speak in a monotone or cup the ear to hear better. If someone has become hearing-impaired in this way, it is easiest to communicate by looking directly at the person while using normal facial gestures, enabling the person to read lips. The outer ear, or pinna, focuses sound waves on the eardrum, which changes differences in air pressure into movement of bones . This movement shakes a liquid, which causes fine hairs to vibrate, a vibration that is felt by nerves and transmitted to the brain . Hearing, then, is a complex process that can go wrong at various places along the way.