How does the study today of 'culture' differentiate itself from, say, the critical theory which sociologists developed in the sixties, if one takes sociology to be "the study of society"?

I don't believe that cultural studies is a social science. Either we're products of the reactionary turn or we're right. Sociology cannot be an ersatz for philology. If you abandon philology just because the philologies don't reflect upon their own medium, you don't necessarily have to abandon the one positive thing about philology, namely, its reference to a specific medium, to talk instead about a non-specific 'society' which no one can grasp. That's the reason why we're here at this Institute. The philological sciences work almost exclusively with books but don't write a single word on the book in the course of its historical transformations. Just because you broaden your analysis from the medium 'book' to include the numerous media that constitute a culture, you don't have to throw everything away. Even Luhmann is at wit's end. He is the best German thinker at the moment, but what 'society' is, no one can say. Luhmann declares it to be useless for his purposes.