I mean, Vader still regularly recollected the memories of his past, but he [Vader] got to a point where he no longer thought of himself as ever having been Anakin Skywalker. As far as Vader was concerned, he and Anakin were two completely separate people -- he even referred to Anakin as "The Jedi"; never as himself.
Zahn confirmed this in an interview:
StarWars.com: Speaking of Anakin, Darth Vader has compartmentalized his own life, not even thinking of his past self as Anakin Skywalker, but as "The Jedi." What does this say about him?Timothy Zahn:
Vader doesn't even think of himself as once having been Anakin Skywalker. Those memories are somebody else's.