Home sign (or kitchen sign) is the gestural communication system developed by a deaf child who lacks input from a language model in the family. This is a common experience for deaf children with hearing parents who are isolated from a sign language community. Home sign (or kitchen sign) is the gestural communication system developed by a deaf child who lacks input from a language model in the family. This is a common experience for deaf children with hearing parents who are isolated from a sign language community. While not developing into a complete language (as linguists understand the term), home sign systems show some of the same characteristics of signed and spoken languages, and are quite distinguishable from the gestures that accompany speech. Words and simple sentences are formed, often in similar patterns despite different home sign systems being developed in isolation from each other. Comparisons are often made between home sign and pidgins. There is great disparity among families with respect to the extent to which family members attempt to learn or participate in the signing of the deaf child. In many cases, no one but the deaf child attempts to sign more than minimally. When two or more children in a family are deaf, however, a more sophisticated private language develops. Linguists have been interested in home sign for the insights it offers into the uniquely human ability to generate, acquire, and process language in general, and particularly as it pertains to such topics as the origins of language, notions of linguistic universals, the hypothesized critical period for language acquisition, children's natural tendency to invent language (language acquisition device), and the relationship between gesture and language. The experience of home signers is contrasted with that of feral children who, with no human social interaction, develop no language at all. Nancy Frishberg set out a framework for identifying and describing home-based sign systems in 1987. She states that home signs differ from sign languages in that they: For example, the alleged Rennellese Sign Language of the Solomon Islands was used by a single deaf individual and his friends and family, and ended with his death. Home sign is often the starting point for new deaf sign languages that emerge when deaf people come together. For example, following the establishment of the first deaf schools in Nicaragua in the 1970s, the previously isolated deaf children quickly developed their own sign language, now known as Nicaraguan Sign Language, from the building blocks of their own diverse home sign systems. For several reported sign languages, it's not clear if they are a collection of home sign used by various families, with similarities due to the common system of gestures used by the hearing population augmented by mime, or an incipient coherent sign language. Such systems include Marajo Sign Language in Brazil, described primarily between deaf mothers and their young children, Maxakali Sign Language, also in Brazil, which is at the least is a very young language, and Mehek Sign Language in northwestern Papua New Guinea, in which signs are quite variable between families, with only a few dozen held in common, all of which are highly mimetic. Home sign also played a part in the formation of American Sign Language, which is a blend of home sign, Old French Sign Language, Martha's Vineyard Sign Language and Plains Indian Sign Language. According to Anne Sullivan, Helen Keller had developed over sixty home signs long before she was taught to communicate through finger spelling.