The use of sign language has a long history. Indeed, humans' first languages may have been expressed through sign. Sign languages have been found around the world, even in communities without access to formal education. In addition to serving as a primary means of communication for Deaf communities, sign languages have become one of hearing students' most popular choices for second-language study. Sign languages are now accepted as complex and complete languages that are the linguistic equals of spoken languages. Sign-language research is a relatively young field, having begun fewer than 50...