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Language acquisition is a natural process in which infants and children develop proficiency in the 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 following 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.

Sign Language Acquisition
Sign languages are natural languages with the same linguistic status as spoken languages. Sign languages are fully accessible to deaf children as they are visual, rather than aural, languages. Approximately 5% of deaf children are born to deaf parents who sign. These babies acquire sign language from birth and their language acquisition progresses through predictable developmental milestones. Babies acquiring a sign language produce manual babbling, akin to vocal babbling, produce their first sign, and produce their first two-word sentences on the same timeline as hearing children acquiring spoken language. Deaf children with hearing parents often have a delayed process of sign language acquisition, beginning at the time when the parents start learning a sign language or when the child attends a signing program.

Because sign language is a visual language, eye gaze and eye contact are critical for language acquisition and communication. Studies of deaf parents who sign with their deaf children have shed light on paralinguistic features that are important for sign language acquisition. The use of child directed signing, akin to child directed speech, involves modifying signs in a way to make them visually salient to children especially in situations without direct eye contact. Another important feature of language acquisition that affects eye gaze is joint attention. In spoken languages, joint attention involves the caregiver speaking about the object that the child is looking at. When using sign languages, children learn to adjusts their eye gaze to look back and forth between the object and the caregiver’s signing.

Spoken Language Acquisition
Because 90-95% of deaf children are born to hearing parents, many deaf children are encouraged to acquire a spoken language. Deaf children acquiring spoken language use assistive technology such as hearing aids or cochlear implants, and work closely with speech language pathologists. Due to hearing loss, the spoken language acquisition process is delayed until such technologies and therapies are used. For children using hearing aids, spoken language outcomes in deaf children are correlated with the amount of residual hearing the child has. For children with cochlear implants, spoken language outcomes are correlated with or the amount of residual hearing the child had before implantation. Spoken language outcomes in deaf children with cochlear implants are highly variable.

For a detailed description of spoken language acquisition in hearing children see: Language acquisition.

Bilingual Language Acquisition
Some deaf children acquire both a sign language and a spoken language. This is called bimodal bilingual language acquisition. Bimodal bilingualism is common in hearing children of deaf adults (CODAs). One group of deaf children who experience bimodal bilingual language acquisition are deaf children with cochlear implants who have deaf parents. These children acquire sign language from birth and spoken language after implantation. Other deaf children who experience bimodal bilingual language acquisition are deaf children of hearing parents who have decided to pursue both spoken language and sign language. Some parents make the decision to pursue sign language while pursuing spoken language so as not to delay exposure to a fully accessible language, thereby starting the language acquisition process as early as possible. While some caution that sign language might interfere with spoken language, other research has shown that early sign language acquisition does not hinder and may in fact support spoken language acquisition.

Language Deprivation
Language deprivation occurs when a child is not immediately exposed to an easily and naturally accessible language during the critical period of language acquisition. The majority of children with some form of hearing loss cannot easily and naturally acquire spoken language. Naturally, this puts deaf children at a real disadvantage compared to hearing peers and places them at risk for serious developmental consequences such as neurological changes, stunted socio-emotional development, delays in academic achievement, limited employment outcomes, and poor mental and physical health.

(For Methods Section)

For a review of educational methods including signing and spoken language approaches, see: Deaf education