I imagine it would probably result in a very loud but incomprehensible burst of static whenever he does that. I'm guessing he doesn't really spend more than a few seconds (hours) at a time slowed down, so it would most likely result in him thinking like a normal guy most of the time, with occasional jump-cuts which make him skip over to a completely different train of thoughts. Memory readers could probably decode what happened by analyzing him for some time, while thought readers would just get confused at his sudden shift in focus, unless they also have [I]extremely[/i] enhanced intellect, in which case they might catch a word or two.

But I'm not really a GM, nor the writer of a telepathic character, so it's not really my place to say, I'm just throwing that out there.