"What is Deaf culture? Has anyone studied it from a sociological perspective?"
Sociological perspective about any subject varies widely but it is all the same in a sense that people act the way they do with a list of reasons. Put a hearing persons life into a sociological perspective within our own "classification" of species, their are clics/groups of people that have formed based on what that group have come up with. For example, in high school there was the jocks, preps, and geeks. These groups formed by characteristics or personalities that have been established.Although deaf community is a different group of people in hearing peoples world, people who are deaf have groups within their culture as well.