From time to time, especially in the evenings, I have to put on my heavy practice mute. Besides the dead sound, what annoyed me most was that I could not watch the bow touch the strings. So I thought, after two years of practice, I really should be able to play without watching myself!
Closed my eyes - and was pretty surprised! Everything seems to improve, be it tone, expression, rhythm, "bow steering", but also intonation and shifting... It seems to be way easier to find the right technique rather by ears that by eyes, especially bowing. After a week of integrating this into my daily practice routine, watching the bow immediately produces a feeling like stumbling over my own feet. Only double stops and large string crossings suck, but I'm sure it's simply a matter of training. Sure this will also be fine for sight reading.
Do you practice with eyes closed? Why and what do you expect from it? And to the teachers out here, do you usually recommend this to your students? (My teachers never asked me to...)
I don't practice with eyes closed, but I have had to do the next thing to it -- namely, practice in near-darkness. In the aftermath of the Alabama tornadoes of April 27, 2011, my part of the city was without power for about 103 hours -- just over 4 days. No damage in immediate area; but one twister had taken out the feed from Browns Ferry Power Plant, about 35 miles west, and that's what plunged us into darkness.
I have very poor near vision, so I never look at fingerboard/bow. So I'm basically playing blind.
Of course, closing the eyes is the best way to increase the focus of our ears and to listen better. Very necessary to improve one's tone.
My teacher had me do this just last night.
If you play in an orchestra you'll be looking at the music in front of you and the conductor (who?). There just isn't the time to be looking at what your fingers and bow are doing, and if you feel the need to do so then more work in the practice room is indicated.
By the way, it is not considered a good idea to move the violin further to the left. A lot of teachers recommend that you have it more to the right and look down the fingerboard to the scroll and at the music which the scroll is pointing at. (Zuckermann for example is very big on this idea). You do not have to look at the bow or your left hand fingers, and I never do, although some players do watch the bow position on the string. I use the Russian bow hold and flat hairs on the strings, which seems to take care of itself.
There are many videos of soloists playing with eyes closed or nearly so at times, presumably for focus, which would include tuning out the photographer and audience perhaps. I tried playing with eyes closed not long ago, and found that I didn't sound like a soloist, just someone more aware of my own clumsiness. Also hard to read the music that way.