Hmm. By lack of concentration, I mean that I know (or think I know) the notes so well that my mind wanders. I.e., what's for dinner? Did I turn the coffeepot off? Things like that. But there are many times when I don't really think about the notes either, because I've been playing them for so long.
It seems like my learning curve is going backwards: for a while I was climbing the hill, and the pieces were getting better and better; I had one great lesson where my teacher was very happy with how they sounded; and now everything is downhill again, degrading instead of improving.
Thank you for the threads - I had actually read two of them before and am using Bernhard's practice/memorization method now for all my new pieces. These two that I'm having issues with, though, were ones that I had memorized before reading Bernhard's enlightening posts. So maybe I am just paying for my ignorance.