Carolyn Kunin is not necessarily describing the so-called "MPD": she states that Shade suffered a stroke that created his delusional state as Kinbote. This is not MPD. ...
Actually Jansy, I do think that VN had the phenomenon of multiple personality in mind - - and his use of the word "automatic man" to describe Gradus is one of the clues. In my reading on multiple personality I found frequent references to automatic writing and other automatisms such as sleep walking in the literature on the subject.
The gun Gradus carries, by the way, is also an "automatic."
Carolyn