3 Sign languages

This session has been exploring the acquisition of sounds as if this was the only medium that can carry language, but of course this overlooks the many signed languages of the world.

Figure 2 There are about 200–300 signed languages that exist today, which in the case of Indo-Pakistani Sign Language represents at least 7 million native signers (Eberhard et al., 2023).

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A photograph of an adult and a child communicating using sign language.

Figure 2 There are about 200–300 signed languages that exist today, which in the case of Indo-Pakistani Sign Language represents at least...

Signed and spoken languages share many properties: both signs and words are conventional, largely arbitrary form-meaning pairings that must be learned from generation to generation. Signed and spoken languages combine smaller units of language into bigger units of meaningful language. For example, signed languages combine hand shape, hand orientation, location in the signing space, movement and non-manual expression into larger meaningful combinations.

Because signed and spoken languages go through the same process of cultural transmission, they can evolve to be mutually unintelligible from one another, as is the case with American Sign Language (ASL) and British Sign Language (BSL). They are also independent of their spoken ‘counterparts’, for example ASL grammar has more in common with spoken Japanese than it does with the speech of Americans.

Signed languages also follow a similar developmental sequence to spoken language, provided infants receive enough high-quality communicative interactions. For instance, infants who experience early sign language from caregivers begin to babble with their hands. Manual babble occurs around a similar age as vocal babble, from 6 to 12 months (Mayberry and Squires, 2006). The first 10 signs are produced around 12 months of age, and the first 50 signs emerge at 24 months and older (Anderson and Reilly, 2002). Just as in spoken language, these first words reflect what is important to the child: for instance words for people, animals and food.

Children learn to combine signs once they have a vocabulary of around 100 signs, typically between 18 and 24 months of age. By 30 months they have command of the basic word order of the language including how to use this flexibly in certain communicative contexts and around 42 months they are beginning to master more complex grammatical features (Lillo-Martin and Henner, 2021).