From the late seventeenth century through the mid-twentieth century, most residents of
Martha's Vineyard were
bilingual in both
English and the local
sign language.
The sign language used during that time were probably somewhat related to the sign language used in the English county of Kent in the 1600s. When the Puritans began moving to the New World, the deaf members of the community brought their sign language with them. This developed into Chilmark Sign Language (named for the Martha's Vineyard town of Chilmark, which had a large deaf population), which was used from the late seventeenth century until the mid-to-early eighteenth century, when it began to change once more.
While MVSL was similar in many respects to American Sign Language, it is more likely that ASL first borrowed signs and structure from MVSL than the other way around. Today's ASL is partly based on French Sign Language, which was introduced here by Laurent Clerc in 1817, but some of it was creolized with existing sign languages - including, most likely, MVSL. But the island's indigenous sign language probably took on more characteristics of ASL after its children began to attend the American School for the Deaf around 1850; when they returned home to Martha's Vineyard they introduced more of ASL to the isolated island's deaf population. This new Martha's Vineyard Sign Language was used in the nineteenth and twentieth centuries until the number of deaf residents dwindled to virtually none.
Some families from the island moved to the Sandy River area in Maine, and the sign language that was used there was probably strongly related to MVSL.
Source: Groce, Nora Ellen. Everyone Here Spoke Sign Language. Pages 73-74.