Animisha Molly Gebrian says that if you want to fix a mistake in a passage, and you practise it playing both correctly and incorrectly, you reinforce both the good and the bad neural pathway for playing this passage. Therefore you should play it correctly ten times in a row.
I've been mulling this over. I don't think "ten times in a row" is the best strategy, and I'm wondering if Molly Gebrian has experimental data to back this up.
It's clear that you need to reinforce the correct neural pathway and let the incorrect one get forgotten. To achieve this, it's not the number of repetitions in a row that counts, it's ensuring (as far as possible) that each time you play the passage, you don't make the mistake.
Even if I play the passage correctly ten times in a row today, maybe because I'm in a particularly calm and concentrated state of mind, this doesn't mean I've already forgotten the incorrect version. It could well be that tomorrow I'm not so focused, and I mess up the passage again.
Forgetting the old, incorrect version doesn't happen in a day. The more often I've played the incorrect version, the longer it will take for it to be forgotten. There's no shortcut: I need to be patient.
So here's what I do (if I can be disciplined enough to follow my own advice!):
- Whenever I'm practicing the piece, each time I get to the passage in question, I stop before it.
- I remind myself what was the reason I messed up: for instance, I was missing a leap because my back muscles were stiffening.
- I play it through, once, very slowly, paying particular attention to the part I might mess up.
- Was it correct? Did I use the fingering I've decided? Did it feel comfortable? Did it sound good?
- If I can answer all those questions with "yes", I play it again, slightly faster. If not, I know that I must go back to more detailed practice on the offending spot.
- If it goes well, I may play it through a few times more, but never more than three or four and always with the utmost concentration.
- In the best of cases, I didn't make the old mistake at all. In the worst of cases, I made it once.
- That's enough for now! If I keep repeating the passage, there's a danger that I may become less concentrated, start playing mechanically and make the old mistake again. Much better wait until this evening, or tomorrow, and approach the passage once more with a fresh mind and total concentration.
The process of replacing the old incorrect version by the new correct one may take days, even weeks if it's a really old, ingrained mistake. During this process I will have played the bad version only a few times, and the good one many, many times, but never ten times in a row.