Dana Dragunoiu has also written about VN's monism in the context of
Berkeley, both in a Nabokov Studies article (“Dialogues
with Berkeley: Idealist Metaphysics and Epistemology in
Nabokov’s Bend Sinister.” Nabokov Studies 5 (1998/1999): 47-62) and
in her dissertation, " 'The Universe Embraced by Consciousness':
Nabokov's Philosophical Domain. " (U of Toronto, 2000).
The original quotation is a few pages before the one mentioned in
Michael Glynn's message--precisely, on page 85.
I don't have time just now to provide a review of all the materials;
Dragunoiu's dissertation survey is more comprehensive than my own brief
treatment (in Jane Grayson et al., Nabokov's World, Palgrave
2002). It is a very rich topic.
Stephen Blackwell