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.
Sign language has been studied by linguists in more recent years and it is clear that even with all the variations in culture and style, they are rich in expression, grammar, and syntax. They follow Noam Chomsky's theory of 'Universal Grammar'. This theory proposes that children will be able to acquire language when brought up under normal conditions and distinguish between nouns, verbs, and other functional words. Before the development of schools for the deaf around the world, deaf children were not exposed to "normal conditions." The similarities between signed language acquisition and spoken language acquisition, discussing process, stages, structure, and brain activity were explored in several studies L.A. Petitto, et al. For example, babbling is a stage of language acquisition also seen in signed language. Additionally, lexical units affect the learning of all languages, as proposed by B.F. Skinner related to behaviorism, which are used in both spoken and signed languages. Skinner theorized that when children made connections in word-meaning association, their language developed through this environment and positive-reinforcement.
Background Human languages can be spoken or signed. Typically developing infants can easily acquire any language in their environment if it is accessible to them, regardless of whether the language uses the vocal mode (spoken language) or the gestural mode (signed language).
Because hearing loss exists along a spectrum and because families address the development of their children in a variety of ways, children who are deaf or hard of hearing proceed along a variety of paths toward acquiring their first language. Deaf children who are exposed to an established sign language from birth learn that language in the same manner as any other hearing child acquiring a spoken language. Acquisition of a signed language like American Sign Language (ASL) from birth is rare from a language acquisition perspective as only 5-10% of deaf children are born to deaf, signing parents in the United States. The remaining 90-95% of deaf children are born to hearing, non-signing parents/families who usually lack knowledge of signed languages. A small percentage of these families learn sign language to varying levels and their children will have access to a visual language at varying levels of fluency. Many others choose to pursue an oral mode of communication with their children with use of technology (such as hearing aids or cochlear implants) and speech therapy.
These circumstances cause unique features of sign language acquisition not usually observed in spoken language acquisition. Due to the visual/manual modality, these differences can assist in distinguishing among universal aspects of language acquisition and aspects that may be affected by early language experience.
Acquisition of signed language Children need language from birth. Deaf infants should have access to sign language from birth or as young as possible, with research showing that the critical period of language acquisition applies to sign language too. Sign languages are fully accessible to deaf children as they are visual, rather than aural, languages. Sign languages are natural languages with the same linguistic status as spoken languages. Like other languages, sign languages are much harder to learn when the child is past the critical age of development for language acquisition. Studies have found that children who learned sign language from birth understand much more than children who start learning sign language at an older age. Also, studies indicate that the younger a child is when learning sign language, the better their language outcomes are. There is a wide range of ages at which deaf children exposed to a sign language and begin their acquisition process. Approximately 5% of deaf children acquire a sign language from birth from their deaf parents. 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.
Sign languages have natural prosodic patterns, and infants are sensitive to these prosodic boundaries even if they have no specific experience with sign languages. Six-month-old hearing infants with no sign experience also preferentially attend to sign language stimuli over complex gesture, indicating that they are perceiving sign language as meaningful linguistic input. Since infants attend to spoken and signed language in a similar manner, several researchers have concluded that much of language acquisition is universal, not tied to the modality of the language, and that sign languages are acquired and processed very similarly to spoken languages, given adequate exposure. 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. At the same time, researchers point out that there are many unknowns in terms of how a visual language might be processed differently than a spoken language, particularly given the unusual path of language transmission for most deaf infants.
Language acquisition strategies for deaf children acquiring a sign language are different than those appropriate for hearing children, or for deaf children who use spoken language with hearing aids and/or cochlear implants. Because sign languages are visual languages, 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. Deaf parents are adept at ensuring that the infant is visually engaged prior to signing, and use specific modifications to their signing, referred to as child-directed sign, to gain and maintain their children's attention. To attract and direct a deaf child's attention, caregivers can break the child's line of gaze using hand and body movements, touch, and pointing to allow language input. Just as in child-directed speech (CDS), child-directed signing is characterized by slower production, exaggerated prosody, and repetition. Due to the unique demands of a visual language, child-directed signing also includes tactile strategies and relocation of language into the child's line of vision. 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. Deaf signing parents capitalize on moments of joint attention to provide language input. Deaf signing children learn to adjust their eye gaze to look back and forth between the object and the caregiver's signing. To reduce the child's need for divided attention between an object and the caregiver's signing, a caregiver can position themselves and objects within the child's visual field so that language and the object can be seen at the same time.