I'm impressed more all the time by what seems to me the inescapable fact that literature - because it's made of the common stuff of language - seems more refractory to change in general than the other arts. I think this is true most specifically of prose fiction, probably because of its historical roots in the popular culture. Tchaikovsky would have a great deal of difficulty digging John Cage or any other serious composers since the first World War - much more trouble than Dostoevsky would have understanding Saul Bellow or even, for that matter, Nabokov. Dostoevsky would have trouble understanding Finnegans Wake, but then we who come after Joyce do, too.
He goes on to cite major novelists of the period - Heller, Ellison, Roth, Bellow, Updike and point to the fact that they are not especially innovate in terms of form and technique. I would agree in broad terms, although only broadly. Think of Updike's The Centaur, for example, or The Witches of Eastwick. He then qualifies his own remarks by referring to the stylists - Robbe-Grillet, Calvino, John Hawkes, Gass, Barthelme - but even these writers, he argues, show differences in sensibility and attitude, rather than means. I don't know, I think Barth is having his cake and eating it here. He rightly points to the irrealism of these latter writers as a break from the realism of the pre-modernist era. Surely that is a major shift in literature, within a generation?
And I think that literature has changed again, too, in the near forty years since Barth said this. Literature today is very different from that of the sixties, or the early sixties at any rate. The metaphysical has been replaced by the psychological, nature by the individual, externalism by internalism. There is a shift going on in literature.
I think the difficulty is - and it's one we didn't have in the sixties and seventies - that there are comparatively fewer good novelists. What may be thought of as lack of innovation nowadays is actually more a reflection of lack of ability.