Found the above articles very interesting. Yeah my concentration when playing in front if ANYONE (even my wife) is shot. I can't seem to get rid of the thoughts mentioned herein when trying to perform. Thoughts like 'I think I sound ok', 'I think they will think I play well or I am playing this piece well', etc. as soon as I t.hink these thoughts I just play the wrong notes and often at places where I have never made a mistake in practice. I always conclude that I just don't know the piece well enough, but I can play it perfect when alone. It is a tough one.
I'm new here. Will ask for help for sure, now I am mostly reading.
But this is a solution, and it made dramatic changes for me.
Take a text, 300-400 words. The exercise consists in count them, and concentrate on getting rid of any other thoughts while doing that, disregarding the meaning of those words too. For a long time, it will be impossible though. But that doesn't matter, your concentration will get better just by trying. When a thought creeps in, say NO mentally, and focus back to counting. Don't move lips or say words inside your closed mouth. It has to be a purely mental exercise. As you try, it won't take more than 15-20 words and the focus is gone, you will already plan what to do when you're finished, or think about concentrating, about not thinking, about the meaning of the words, and so on. Just keep going.
In the beginning don't do more than 3-4 minutes per day. On the first day, I did this a few times, one of the sessions lasting 10 minutes, and latter I tried to play the piano. I sat there and could not lift my hand. I probably could have if I really made a big effort, but I felt so exhausted. My head felt like I was wearing a helmet. Some 40 years ago, I got sun sting one summer. This reminded me of that feeling. It took 3 days to feel better again. So do not overdo it. And not before important tasks, at least for a while.
Note that it's concentration on a task, not clearing your mind.
To avoid making a too long post, will keep details of how it worked for me for another time, but it changed my life, even though I didn't manage to keep it up for long.