tl;dr No. Cultural studies are focused on specific cultural phenomena, including literature. Theory is at a level of abstraction from those phenomena.
Culler makes the following statements here:
- Culture, broadly defined, is "'signifying practices', the production and representation of experience, and the constitution of human subjects".
- Cultural studies is the study of culture thus defined.
- Theory is an abstraction that draws upon insights and techniques from a wide range of fields to discuss the mechanisms of signification, cultural production and representation, and subject-formation.
We could map the relationships and explain them with this analogy:
theory : cultural studies : culture ::
theoretical sciences : applied sciences : nature
Consider the term "applied sciences". We know roughly what the term means, and how those sciences differ from theoretical sciences. But is it easy to define "applied sciences" exactly? At best, we could come up with a broad definition that would tell us very little about what exactly is entailed in the actual practice of an applied science. Even the subject of study is not particularly well-defined: "nature" and "culture" are extremely wooly terms. If "applied sciences" is difficult to define, so is "cultural studies", and for the same reason. They're umbrella terms that cut across disciplinary boundaries.
Literature is, of course, a cultural phenomenon, in the sense that Culler defines culture. That is to say, it involves "signifying practices"; "the production and representation of experience"; and "the constitution of human subjects".
- As a linguistic expression, literature is a signifying practice. Insofar as literary language is thought of as a special use of language, literature is even its own signifying practice. As a very basic example, a poet who writes a sonnet is relying on a whole tradition of sonnet-writing. The meaning of her sonnet depends on the fact that it is a sonnet, and readers know what to look for: is it a Shakespearean or a Petrarchan sonnet? Something else? Where is the volta? Is there a couplet at the end? Is it a stand-alone sonnet or part of a sequence? These sorts of questions arise simply because the choice of this particular form signifies something. It's not arbitrary, but it makes meaning for the writer and the reader.
- Literature depicts aspects of experience, and the act of reading itself is an experience. So literature is involved with "the production and representation of experience".
- "The constitution of human subjects" is difficult to explain easily. One example might be that if a child reads a book about someone in a wheelchair who leads a full life, or about another child who has two parents of the same sex, that child becomes a certain sort of person—one who does not see disability as a limitation, or who accepts same-sex parents as being as unremarkable as opposite-sex parents. Literature shapes what kind of person we are. A more sophisticated way of thinking about this is to consider the reading subject. Let’s say someone asks two people how they're spending their time in quarantine. If one person says, "I've been watching a lot of TV" and the other says "I've been reading a lot of poetry", we draw certain conclusions about the kind of person each of those individuals is. More tellingly, the speakers might present themselves as specific sorts of individuals: for example, “I’m just not a poetry person”.
These are all very reductive ways of explaining literature as a cultural practice in Culler's sense, but they're at least a starting point. To study literature in this way—as a signifying practice, as producing and representing experience, as constitutive of the human subject—is to make literary studies a part of cultural studies. This approach breaks down the barriers between the "literary" and the "non-literary". Someone studying, say, Charlotte Brontë's Shirley, which deals with the Luddite revolt, from a cultural perspective might spend as much time on these as on the specifics of Brontë's novel:
- the representation of craftsmanship as opposed to mass production in the Victorian era
- the way in which “women’s work” such as spinning and weaving became part of men’s labor in the factories
- what was said about the Luddites in sermons, newspapers, or pamphlets
- the government’s response to the Luddites.
Shirley becomes, in this sort of reading, a cultural artifact that responds to and shapes the discourse around the Industrial Revolution. Its value lies in how it illumines its specific historic moment rather than on some aesthetic criteria peculiar to literature.
But this is to study literature from a perspective informed by theory. It isn't theory per se, which involves a layer of abstraction from the object of study. For example, a theoretically informed reading of Shirley might say that its characterization of textile workers laid off due to industrialization as "good" or "bad" individuals permits systemic causes of inequality to be disguised as character defects. (Note: I'm not making this argument, I'm saying it could be made about that novel.) A theoretical argument, on the other hand, would be something like:
Dominant cultural discourses represent the dispossessed in a way that disguises social iniquities as character flaws. They do so by positioning the subject as an autonomous agent capable of moral choice rather than as a constrained position determined by economic forces.
(Again, I'm not making this argument, I'm saying it theoretically could be made.) Such an argument would require insights from economics, particularly Marxist-inflected; psychology; moral philosophy; and semiotics, or the study of representation. None of these far-ranging fields is specifically literary. Just as there is no barrier between literary studies and cultural studies, there is no specifically literary theory that can be set off from wider theoretical arguments about cultural forces generally.
With regard to Roland Barthes, calling him a "literary theorist" simply acknowledges that the focus of some of his best known writings (e.g., The Death of the Author) was literature. However, Barthes's writings do not assume that the literary is a separate realm. They work to undermine the tenets of traditional literary criticism, such as the notion that the author's intention determines the meaning of the work. Barthes is a transitional figure whose work marks the movement from a purely literary theory to the broader realm that we now call simply "theory".
To sum up: Cultural studies is an applied field, where theoretical insights are brought to bear on specific cultural phenomena. Literary works, both individually and collectively, are among the phenomena that fall under the remit of cultural studies. They do not have a special status within cultural studies. Theory is a more abstract field. It draws upon insights and techniques from a wide range of subjects: philosophy, economics, psychoanalysis, sociology, linguistics, anthropology, for example. There is no specifically literary theory that is set apart from this amorphous and flexible set of insights and techniques that fall under the umbrella of "theory".