In the 1980s deaf children in Nicaragua invented a completely new sign language of their own.
It was a remarkable achievement, which allowed experts a unique insight into how human communication develops.
"What we learnt from Nicaragua about language still isn't over," says American linguist Judy Shepard-Kegl, who documented the emergence of Nicaraguan Sign Language.
Witness History: The stories of our times told by the people who were there.
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