@dabbler, best we can really say is that we just don’t know if he did or not.
You seem to reach your conclusion that if the man had been dreaming visually, then he’d be better able to interpret the new visual information coming in from his repaired sight. But I think it possible – if not really likely – that maybe the internal visual language in his mind was so radically different than the new information coming from his eyes that it was difficult for him to make the translation.
One analogy I can think of is when I attended Gymnasium (high school) in Germany. I was learning to speak German on the fly, while at the same time attending classes in algebra. Ever try to learn a new language (like math) through a foreign language (like German)? I found it to be nigh impossible.
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My personal opinion is that he probably did not dream visually before having his sight restored as his unconscious had no references to draw upon. It’s just that I think it a fallacy to try and reach that conclusion based upon his performance after the surgery. I wonder if anyone asked that gentleman what his dreams consisted of both pre- and post-op?