Now, this isn't necessarily a strange thing, because I've been playing for a long time and don't always have to pay conscious attention to every single note. But usually when I play Tiersen's work, I at least have to be partially thinking about what bit of the song comes next. On my upright, I didn't at all.
The reason I had such a hard time with this was: I didn't learn his music on my upright. I learned it on my digital piano. Shouldn't any song come more easily to me on the piano on which it was learned? This seemed like some sort of bonkers anti-state-dependent memory at work. I mulled the topic of muscle memory around in my head for a while, and finally dug into Wikipedia a little today to help with some rough thinking:
I realize that there is a lot of research already done around fine motor memory, the psychology of music performance, etc. But this is where my thinking-out-loud-for-fun brain took me.
As I said, my mind went to muscle memory first. At the base level, once someone has played the piano enough, they can play any piano. Quite literally "Like riding a bike." But something I recently read in Piano: The Making of a Steinway Concert Grand – that all pianos have their own personalities, tones, and feels – had me thinking about particulars. There's a reason why, even though I know how to ride a bike, I've always nearly broken my neck when attempting to ride bikes with bullhorn handlebars, yet felt like I could ride the ones with riser handlebars in my sleep. More than just muscle memory for the act of piano-playing, it was THIS piano (my upright) that I spent the most time with; THOSE keys, with their particular width, spacing and weight; THAT bench's distance from the ground and piano itself.
The other circle in that chart, state-dependent memory, represents that piano's environment. It's in the same place in my parents' house that it's always been in – off of the kitchen and under the Verona painting. Also, I'm much more used to the feel of the house I grew up in than I am in an apartment I've been renting for just 2 years (on top of that: my digital piano is in its 5th environment, or apartment, by this point).
So, muscle memory is how pianos can be played interchangeably. And the particulars of muscle memory with a side of state-dependent memory – that piano in that position of that house – is what made my playing the most fluid. Here's another way of looking at it:
I can play almost any instrument with a basic piano keyboard setup – from an accordion to a Schroder-style toy piano. But I'm not very good. I'm better with a proper piano – either acoustic or digital. By "proper," I mean all 88 keys that are weighted. Next comes any acoustic piano. As awesome as brands like Casio and KORG have gotten at simulating acoustic pianos with their digital versions (I have a Casio, and I love it), there is just no substitution for the feeling of hitting a key that subsequently makes a tiny hammer hit a string. And finally, my most familiar piano. This is why I think it doesn't matter at this point which piano I actually learned a song on: I'll always be better at it on that one upright.
For your supplementary fun:
Muscle memory (Wikipedia)
State-dependent learning (Wikipedia)
A page on sight-reading and memory (from The science & psychology of music performance)
My favorite Yann Tiersen-related video ever: Dave Thomas playing La Noyee on accordion
