I bought a plastic mat to put underneath my desk chair, to protect the wooden floor from having bits of stone ground into it by the chair wheels. But it kept sliding when I stepped onto it, nearly sending me stumbling into my large, expensive, and fragile monitor. I decided to replace the mat as soon as I found a better one.
Before I found a better one, though, I realized I wasn't sliding on it anymore. My footsteps had adjusted themselves to it.
This struck me as odd. I couldn't be sensing the new surface when stepping onto it and adjusting my step to it, because once I've set my foot down on it, it's too late; I've already leaned toward the foot in a way that would make it physically impossible to reduce my angular momentum, and the slipping seems instantaneous on contact. Nor was I consciously aware of the mat anymore. It's thin, transparent, and easy to overlook.
I could think of two possibilities: Either my brain had learned to walk differently in a small, precise area in front of my desk, or I noticed the mat subconsciously and adjusted my steps subconsciously. The latter possibility freaked me out a little, because it seems like the kind of thing my brain should tell me about. Adjusting my steps subconsciously I expect; noticing a new object or environment, I expect to be told about.
A few weeks later, the mat had gradually moved a foot or two out of position, so I moved it back. The next time I came back to my desk, hours later, having forgotten all about the mat, I immediately slipped on it.
So it seems my brain was not noticing the mat, but remembering its precise location. (It's possible this is instead some physical mechanism that makes the mat stick better to the floor over time, but I can't think how that would work.)
Have any of you had similar experiences?
Based on my own experience, it seems like 'muscle memory' means your brain learning abstractions of motion. So when you know how to ride a bike, you only have to consciously think 'turn left' rather than 'move my right hand forward and pull my left hand back and lean a little bit to the left'. These abstractions are not just recordings, as they can vary along one or more dimensions: you can turn sharply left or gently left, and your 'muscle memory' knows how to implement that.
'Sit in my desk chair' might also be a learned abstraction that involves navigating the slippery mat.
That isn't how you turn left on a bicycle, consciously or otherwise. If you do that you will fall off to the right. What you actually have to do is control your rate of falling over at close to zero while also controlling the rate of turning at a desired value. This cannot be done by memorising any mapping from desired turn rate to anything that you do with your muscles. A bicycle is an unstable system that the rider must continuously maintain his balance on.