Manual babbling is a linguistic phenomenon that has been observed in deaf children and children born to deaf parents and appears at the early stages of language acquisition. It is characterized by repetitive movements that are confined to a limited area in front of the body similar to the sign-phonetic space used in sign languages. In their 1991 paper, Pettito and Marantette concluded that between 40% and 70% of deaf children's hand movements can be classified as manual babbling.