I would like to make a distinction, and clear up a potentially confusing misconception that could be brought about by this sentence, written by the original poster.occurin wrote: This is a pity, because I really need to memorize pieces, so I can internalize the music and develop my "mental play".
Mental play has more in common with aural skills (hearing the music in your head and being able to translate that to the piano through your fingers) than memorisation. While memorising and mental play are somewhat related, they are also totally different. Memorisation does not necessarily involve mental play (it doesn't have to involve mental play at all, actually), but mental play complements and solidifies memorisation. If you had to choose only one of them to work on, then choose mental play. That is far more important to overall musical development than memorising. I will define what memorising and mental play are in this post.
Before I do that though, let me say that you can memorise music using Synthesia alone, but it is a lot more difficult and much slower to do without musical theory knowledge. There are threads I made in the "General" section of the forum, in which I have posted videos of two of the three pieces I performed for my previous piano exam, along with how I used Synthesia to help me prepare the pieces for the exam. However, I did have some familiarity with the pieces already (before drilling them with Synthesia) because I had to learn them from sheet music first.
I would define mental play as "hearing the music in your head, with notes and expression intact - hearing the music as if you performed it perfectly to your own liking". I would define memorisation as more of a visualisation thing, sort of like this: you know how there are YouTube tutorials for songs, where you are looking straight down from above at the piano keyboard, and seeing someone's hands and fingers on the notes as they play? Memorisation is like that - it is as if you are viewing yourself playing the piano, looking down on yourself from above. Synthesia is perfect for this, because you already have the keyboard in front of you on the screen! The only thing you do not have is your hands and fingers on the keys of the keyboard. Therefore, you can see that memorising and mental play are different, but related concepts. One deals with the physical, the other deals with the sound. This is why they are complementary.
Nicholas has been playing with the idea of live video feeds in Synthesia anyway. If that feature ever makes it in, Synthesia will be an amazing memory aid.
Anyway, I hope that sheds some light on why memorising and mental play are two different, but complementary things.