How to keep singing while playing?

[pianoman53]

I recently discovered that the reason that I play wrong notes mostly aren't because of technical difficulty, but rather because I lose my focus for a short time.
When I keep listening and "singing along" in my head, I can play most of my repertoire withour that many mistakes, but once I stop doing that, because of lack of focus, the risk to make mistakes obviously increases. 

Do you have the same experience, and maybe some advice on how to increase the ability to focus for a long time?

[ryankmfdm]

 I've wondered about this before, myself. What got me thinking about it in the first place was noticing how Gould would always hum along as he was playing.

[indianajo]

I find when I learn a piece, first I learn the right hand part, then the left hand part, then I slowly put them together.  It has to be slow because I can't read the music that fast.  Then as my lower brain memorizes the movements I can speed up.  At some point I lose interest in looking at the printed page and my eyes wander, letting my lower brain play back the movements as I get into the beauty of the piece.  During this period I find sometimes i make more mistakes than previously, as I play out false memories while I am ignoring the visual cues.  Then I catch these mistakes, and learn the proper movements.  It is here where a teacher can save time, by hearing the mistakes and circling them with pencil for my attention. Sometimes I can make up plausible chords or sounds that aren't the right ones.  If no teacher, taking a break of months and coming back can focus my eyes on the page again and point out to me the mistakes I have been making. 
The audio track is rather separate for me, more something that happens when I am away from the piano when I wish to hear the piece.  It runs through my head while I'm doing something not taxing to that part of the brain, like riding a bicycle or following pipes to document them.  I also while asleep dream parts of pieces I work on that i can't play yet. 
I also now sing audibly with some pieces, which is like running the third hand (or fifth if I am playing bass lines with my feet on the organ).  Words are kept in a a radically different part of my brain, and I have been known to make up plausible sounding lyrics instead of the right ones.  The music part remembers some sounds, then the word part tries to make up words that go with those sounds.  I'm still rather addicted to lead sheets to sing the lyrics, as my brain runs off to the make up the plausible instead of the original artists creation. 

[lateromantic]

I recently discovered that the reason that I play wrong notes mostly aren't because of technical difficulty, but rather because I lose my focus for a short time.
When I keep listening and "singing along" in my head, I can play most of my repertoire withour that many mistakes, but once I stop doing that, because of lack of focus, the risk to make mistakes obviously increases. 

Do you have the same experience, and maybe some advice on how to increase the ability to focus for a long time?

You should be very careful that your "singing along" is only in your head and not out loud.  Otherwise, as I found out the hard way, you'll have a bad habit that you will have to work on breaking for decades to come.  I think it may have started in college, when my teacher told me that I should make the music "sing" and I took that a little too literally.

I'm not sure what to tell you about your focus problem, since my problem is the opposite:  I get so wrapped up in the music that I lose all track of time.