Language acquisition is a natural process in which infants and children develop proficiency in the first language or languages that they are exposed to. The process of language acquisition is varied among deaf children. Deaf children born to deaf parents are typically exposed to a sign language at birth and their language acquisition follows a typical developmental timeline. However, at least 90% of deaf children are born to hearing parents who use a spoken language at home. Hearing loss prevents many deaf children from hearing spoken language to the degree necessary for language acquisition. For many deaf children, language acquisition is delayed until the time that they are exposed to a sign language or until they begin using amplification devices such as hearing aids or cochlear implants. Deaf children who experience delayed language acquisition, sometimes called language deprivation, are at risk for lower language and cognitive outcomes. However, profoundly deaf children who receive cochlear implants and auditory habilitation early in life often achieve expressive and receptive language skills within the norms of their hearing peers; age at implantation is strongly and positively correlated with speech recognition ability. Early access to language through signed language or technology have both been shown to prepare children who are deaf to achieve fluency in literacy skills.
History
Sign language has been cited in texts as early as the time of Plato and Socrates, within Plato's Cratylus. Socrates states, "Suppose that we had no voice or tongue, and wanted to communicate with one another, should we not, like the dumb, make signs with the hands and head and the rest of the body?" Western societies started adopting signed languages around the 17th century, in which gestures, hand signs, mimicking, and fingerspelling represented words. Before this time, people with hearing loss were categorized as to be "suffering" from the disease of deafness, not under any socio-cultural categories like they are today. Many believed that the deaf were inferior and should learn to speak and become "normal." Children who were born deaf prior to the 18th century were unable to acquire language in a typical way and labeled "dumb" or "mute", often completely separated from any other deaf person. Since these children were cut off from communication and knowledge, they were often forced into isolation or into work at a young age since this was the only contribution to society that they were allowed to do. Society treated them if they were intellectually incapable of anything.
The problem was lack of education and resources. Charles-Michel de l'Épée was a French educator and priest in the 18th century who first questioned why young deaf children were essentially forced into exile, declaring that deaf people should have the right to education He met two young deaf children and decided to research more on "deaf mutes", attempting to find signs that were being used in Paris so that he may teach these young children to communicate. His success resonated throughout France and he later began teaching classes for this new language he had pulled together. He soon sought out government funding and founded the first school for the deaf, the National Institute for Deaf Children of Paris around the 1750s & 1760s. This school continued to operate after his death in 1789 by his student, Abbe Roch-Ambroise Cucurron Sicard.
Sicard asked the question of the deaf, "does he not have everything he needs for having sensations, acquiring ideas, and combining them to do everything we do?" He explained in his writings that the deaf simply have no way of expressing and combining their thoughts. This gap in communication created a huge misunderstanding. With this new development of a system of sign, communication began to spread throughout the next century among the deaf communities around the world. Sicard had the opportunity to invite Thomas H. Gallaudet to Paris to study the methods of the school. Here, Gallaudet met with other faculty members, Laurent Clerc and Jean Massieu. Through their collaboration, Gallaudet was inspired to begin his teachings for a school of the deaf in the United States, later known as Gallaudet University, founded in 1864.