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Uncalled, a memory floated into his mind. He saw a candle-lit room with a vast white counterpaned bed, and himself, a boy of nine or ten, sitting on the floor, shaking a dice-box, and laughing excitedly. His mother was sitting opposite him and also laughing.
He pushed the picture out of his mind. It was a false memory. He was troubled by false memories occasionally. They did not matter so long as one knew them for what they were. Some things had happened, others had not happened […]. (3.6.34-36)
After being brainwashed, Winston experiences overactive crimestop and doublethink, as evidenced by the occasional "false memories" he never used to doubt.
"Do you realize that the past, starting from yesterday, has been actually abolished? If it survives anywhere, it's in a few solid objects with no words attached to them, like that lump of glass there. Already we know almost literally nothing about the Revolution and the years before the Revolution. Every record has been destroyed or falsified, every book has been rewritten, every picture has been repainted, every statue and street and building has been renamed, every date has been altered. And that process is continuing day by day and minute by minute. History has stopped. Nothing exists except an endless present in which the Party is always right. I know, of course, that the past is falsified, but it would never be possible for me to prove it, even when I did the falsification myself. After the thing is done, no evidence ever remains. The only evidence is inside my own mind, and I don't know with any certainty that any other human being shares my memories. Just in that one instance, in my whole life, I did possess actual concrete evidence after the event – years after it." (2.5.14, Winston to Julia)
Winston feels confident that, despite the Party’s control of information, and thus, the past, he alone had possession of evidence to prove the Party’s wrong – at least in his memory.
Winston could not definitely remember a time when his country had not been at war, but it was evident that there had been a fairly long interval of peace during his childhood, because one of his early memories was of an air raid which appeared to take everyone by surprise. Perhaps it was the time when the atomic bomb had fallen on Colchester. He did not remember the raid itself […]. (1.3.12)
No matter how hard he scrutinizes his memory, Winston is uncertain whether a time existed when Oceania was not at war with someone.