Sentence Correction

Studies have found that deaf children from American families who identify themselves as culturally deaf, and use sign language, are generally on a par with hearing children in terms of reading and writing, because they have been exposed to language since birth.

and use sign language, are generally
using sign language, are generally
use sign language, and are generally
and using sign language are generally
and use sign language, generally

Can somebody explain why there is a comma after "deaf"?

Thanks