I have long maintained that with the invention of the piano notation should have changed to reflect the vastly expanded world of resonance released and revealed by the new instrument. Along with that statement I am quick to add that, had composers actually changed their syntax to match the sound, no one would have known how to deal with it and the instrument would most likely have died the unnatural premature death of the arpeggione and other instrumental novelties of the day, of which there were many.
Along came Schumann. Probably more than any other composer he found ways to require the pianist to connect with sound in an altogether new set of dimensions. He did this by literally stretching beats to occur over long periods of time, with pre-bar bass notes, grace notes, rolled chords, and other devices (mostly annoying to the novice and to the unimaginative) that cannot simply be played but which demand observation, one tone -- sometimes one partial -- at a time.
Also he explored the difference in resonance between black and white key basses: Just look at the Symphonic Etudes. Whole pages can be played with full pedal over a low bass, the vibrations cleaning themselves as the music builds.
Add to that his radical dynamics: long pianissimos, sudden fortes, markings that direct the player's attention to the sound not the execution.
Even Chopin did not go this far into the new territory.
