As part of my ongoing efforts to fix my body structure (which can be pretty poor), I have been trying to get my posture correct for sanchin - head being pulled up from the top, no swayback, not hunching. My problem is, while I have changed my posture in the last little while (and for the better too), my sensei still keeps telling me that I have some of these issues! And no matter how I try and fix it according to his instructions, I haven't had much success.
What I needed was a different perspective. What I was feeling in my body felt 'right', so I couldn't make sense of what he was seeing. So, I videotaped myself. Well, that was a different perspective alright. It turns out, what I was doing, was very different to what I thought I was doing. It took me about 5 minutes after viewing my video and doing another couple of takes until I had what now looked like a posture my sensei had described. It felt very strange, but somehow'right'.
The upshot was, yesterday at training, I was trying to do everything with this 'improved' posture, and while it still feels artificial, I was finding that certain techniques were quicker or had more power behind them as a result, particularly when doing pad work. I also checked with my sensei and I am on the right track (but, as usual, still need some more improvement).
This is where videos are invaluable for learning. Just as person-person instruction is essential for learning a physical pursuit, so too is the ability to truly see what your body is doing. Our bodies lie to us all the time, and while having someone else give feedback can assist us in improving, the raw, uninterpreted footage from a camera gives me a more detailed and comprehensible understanding of what's really going on. I know what I think my body is doing, so when I see it is different, I see how my body is lying to me. A mirror can give similar feedback, but is not as useul, as it only gives front-on views, and is instantaneous with the movement - part of my attention is always on the doing, not on the looking.
But video feedback is only useful if you have the perspective of knowing what it is you are looking for. Without that, what's the point?