Psycholinguistics, Milestones in

American Sign Language (ASL) is a language used by more than 2 million Americans who are deaf. It has the linguistic properties of spoken languages. Through studies of deaf children’s language acquisition, psycholinguists have found that babies can learn ASL from birth and acquire it in almost the same stages and patterns as children acquiring spoken language.

Several researchers have found that this early exposure to language activates the same brain areas regardless of modality—signed or spoken. Importantly, when a language is learned later, different patterns of activation in the brain are seen. An important finding made by Petitto and Marenette is that the plasticity in the brain allows language to be perceived and expressed by the tongue or hands; the brain is not hardwired for speech or sounds. Brains are, however, hardwired to identify aspects of language patterning. Therefore, statistically regular patterns can be found in both spoken language phonology and visual language phonology. The only difference is the modality of language input and the components of the phonology.

Deaf children acquire language in the same way as do hearing children. Newport and Meier reported that language acquisition is facilitated by mothers who use sign language and who make signs on their deaf babies’ bodies, move the babies’ hands, use exaggerated facial expressions, and sign in the baby’s line of vision. This behavior is similar to how mothers behave with their hearing babies. Their vocal tone is varied and facial expression exaggerated, and they use shorter phrases and repeat words.

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Figure 1 An Example of Babbling

Deaf infants do babble before signing a first word. ASL babble uses gestures that resemble signing but does not show full lexical signs, just as hearing children’s babbling sounds like words without using clear adult words. (See Figure 1 for an example of babbling.)

For deaf babies who are exposed to sign language from birth, the first signs typically emerge at about 8.5 months. This is earlier than spoken language emerges, with the first word usually occurring at 10 to 13 months. (See Figure 2 for some examples of signed words.) Studies show that the size and scope of vocabulary words used by deaf children and hearing children are identical. Both children learn one word or sign at a time until they reach their first 50 words. Then they start combining words, generating rapid vocabulary growth.

Visual language phonology includes the handshape, palm location, movement, and physical location of the sign. According to the findings of Crume, these manual phonemes follow a proximal-to-distal trajectory. Here, children’s earliest signs are most accurate in sign location as more proximal joints (shoulders, arms, and elbows) develop first. Next, sign movement becomes more accurate as the elbows and wrists develop more control. Finally, handshape becomes more accurate as children gain more fine-motor muscle control over their hands and fingers. This pattern is also seen in the order of handshapes usage. A study shows that early handshapes include an open or closed whole hand and a pincer grasp (e.g., S, L, baby O, G, and C handshapes). Then one sees children use handshapes that require the outside three fingers (e.g., I, P, 3, V, H, and W). The last manual phonemes to develop are the ones that require bending or crossing of the fingers, including X, R, and T.

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