Wherever communities of deaf people exist, sign languages have developed as useful means of communication and form the core of local Deaf cultures. Sign language should not be confused with body language, a type of nonverbal communication. This is supported by the fact that there is substantial overlap between the neural substrates of sign and spoken language processing, despite the obvious differences in modality. Linguists consider both spoken and signed communication to be types of natural language, meaning that both emerged through an abstract, protracted aging process and evolved over time without meticulous planning. Sign languages are not universal and are usually not mutually intelligible, although there are also similarities among different sign languages. Sign languages are full-fledged natural languages with their own grammar and lexicon. Sign languages are expressed through manual articulation in combination with non-manual markers. Sign languages (also known as signed languages) are languages that use the visual-manual modality to convey meaning, instead of spoken words. Preservation of the Sign Language, George W.
