Persons whose deafness cannot be relieved by medical or surgical means may be greatly helped by various types of electronic hearing aids. Those with hearing loss that cannot be relieved even by mechanical devices (i.e., those with sensorineural deafness) can have special training in speechreading (see lip reading). When deafness is present at birth or develops before a child has learned to speak, it is necessary also to provide specialized speech training and education in sign language, in which fingers and hands are the instruments of expression and communication. Schools and trained teachers for the hearing-impaired are now found in every large city in the world. Other aids for the hearing-impaired include specially trained "hearing dogs," customized telephones, and closed-caption television.