Nobel Prize Novel Opens With Two Friends Who, Apparently, Are Alternate Personalities, in a Scenario Typical of Cases of Multiple Personality (Dissociative Identity)

The novel I referred to in the post of January 1, 2014 begins with the meeting of two friends. Ms. A says, “But do you know something? I discovered while you were away that for a lot of people you and I are practically interchangeable?”

“You’ve only just understood that?” said Ms. B.

They go on to discuss how distinctly different they are from each other in personality and personal appearance. Yet a woman they both know, who is more connected to Ms. B, has, in the latter’s absence, been talking with Ms. A, as if Ms. A and Ms. B were “interchangeable.”

This is a typical experience for two alternate personalities of a person with multiple personality. To them, they are obviously different from each other, and they can’t understand why other people don’t seem to see it. For example, they think they look quite different from each other, and they don’t realize that other people see the same body for both of them.

Where did the author learn this about alternate personalities in multiple personality? After all, when this novel was written, around 1960, there were few readily available nonfiction books that would have described it. So was the author describing her own alternate personalities?