Just to add to that, Erwin Nyiregyhazi is one of the only pianists I've ever heard who can make a sound where he seems to be able to truly control how a sound continues after notes were already struck. Barenboim speaks of such things in masterclasses, but I've never once heard him make any truly out of the ordinary pianistic illusions. From a combination of self experimentations and observations of what Nyiregyhazi does, I've come to the conclusion that he doesn't necessarily make a pure illusion, but exercises some literal control over how notes last (by retaining so many overtones at first, that further fluttering or half pedals can substantially change what is being heard in the overtone series). In his case, he makes few traditional clean pedal changes and almost always carries overtones between pedal changes via half-pedalling. I don't think it's any coincidence that not only does he merge a lot of overtones, but that he can also seem to control sounds after they already occurred. The two are inseparable for me, if we're talking about using pedalling to manipulate sounds that are already happening. Play a chord and wait a couple of seconds and depressing the pedal scarcely changes anything at all. You can do whatever you like after a certain point and nobody will be any the wiser. Only early on after sounding a note does depressing the pedal make it seem to truly "grow" into something, via the new overtones. As soon it's clear and notably decayed, few new overtones arise when the pedal goes down- which means that the pedal can neither add nor subtract anything that will substantially affect what is already there. Play a chord into the pedal however, and any half pedalling or flutter pedalling that happens early on can make a HUGE literal difference to how the sound continues to resonate. If you accept murkiness for a while, you can subtly continue to cleanse overtones in a way that will be perfectly audible, long after the notes were sounded.
If Nyiregyhazi spoke of vibrato, I'd at least humour him (whether it were necessarily real or purely imagination on his part) for no other reason than the remarkable the way in which he seems to control sounds long after the hammer hits strings. However, sorry for being cynical, but having both tried it myself and never witnessed audible vibrato from any other pianist, I'm not going to casually accept that fluttering on a chord that has already been cleaned up (eliminating all scope for significant control over overtones) is going to make any notable difference that exists in reality. If you've found something remarkable, it's for a listener to judge whether the results are genuinely out of the ordinary, not for the pianist doing the experiment. Upload something.