Sutton SignWriting for a master's degree in linguistics. The dissertation "The Writing of Grammatical Non-Manual Expressions in Sentences in LIBRAS Using the SignWriting System" by João Paulo Ampessan states that "the data indicate the need for [non-manual expressions] usage in writing sign language". Sign perception For a native signer, sign perception influences how the mind makes sense of their visual language experience. For example, a handshape may vary based on the other signs made before or after it, but these variations are arranged in perceptual categories during its development. The mind detects handshape contrasts but groups similar handshapes together in one category. Different handshapes are stored in other categories. The mind ignores some of the similarities between different perceptual categories, at the same time preserving the visual information within each perceptual category of handshape variation. In society Deaf communities and Deaf culture When Deaf people constitute a relatively small proportion of the general population, Deaf communities often develop that are distinct from the surrounding hearing community. These Deaf communities are very widespread in the world, associated especially with sign languages used in urban areas and throughout a nation, and the cultures they have developed are very rich. One example of sign language variation in the Deaf community is Black ASL. This sign language was developed in the Black Deaf community as a variant during the American era of segregation and racism, where young Black Deaf students were forced to attend separate schools than their white Deaf peers. Use of sign languages in hearing communities On occasion, where the prevalence of deaf people is high enough, a deaf sign language has been taken up by an entire local community, forming what is sometimes called a "village sign language" or "shared signing community". Typically this happens in small, tightly integrated communities with a closed gene pool. Famous examples include: Martha's Vineyard Sign Language, United States Al-Sayyid Bedouin Sign Language, Israel Kata Kolok, Bali Adamorobe Sign Language, Ghana Yucatec Maya Sign Language, Mexico In such communities deaf people are generally well-integrated in the general community and not socially disadvantaged, so much so that it is difficult to speak of a separate "Deaf" community. Many Australian Aboriginal sign languages arose in a context of extensive speech taboos, such as during mourning and initiation rites. They are or were especially highly developed among the Warlpiri, Warumungu, Dieri, Kaytetye, Arrernte, and Warlmanpa, and are based on