That does make sense, with the way you can create tunnel vision by looking at a small area for too long without glancing away far enough. And one glance will do it - I believe Bates mentioned that people with good vision will periodically glance away from a small area they're studying even if they don't realize they're doing it.
Yes, interspersing longer glances away will help keep those peripheral cells more engaged. Sometimes, when driving, for instance, I find myself getting hung up on fixating too long on a tiny spot (like the little tail
light of the vehicle in front of me), I'll make a few shifts from one side of the road to another, and I find it helps gets my 'full' field of vision back on track, more engaged.
As far as fast enough, I don't remember offhand Bates saying a few times a second (any idea?), but that does sound roughly right. It's always nice to verify things like that, even if Bates did put a lot of time into the research. I don't know, I have a hard time counting. I think faster than 3 or 4 times a second is possible, but that's certainly enough to start with anyway, and a lot better than 1 per second
I probably took that a little out of context. Bates talked about it in his book in the chapter on Shifting and Swinging. He was mainly referring to being able to realize the swing, if shifting was too fast:
"Shifting may be done slowly or rapidly, according to the state of the vision. At the beginning the patient will be likely to strain if he shifts too rapidly; and then the point shifted from will not be seen worse, and there will be no swing. As improvement is made, the speed can be increased. It is usually impossible, however, to realize the swing if the shifting is more rapid than two or three times a second."
Shifting can certainly be done a little faster than that, but the swing may not be realized. Not so big a deal with those who have normal sight. They aren't usually aware of the swing anyways, and don't really have to be, when all is working in good order. But for the sake of restoring vision, with Bates it was a vital feedback mechanism, evidence that one was shifting correctly, not just moving the eyes (moving the attention, seeing best where one is looking). I spent an inordinate amount of time on shifting and swinging (probably a year or two), without much benefit. I got very good at being able to swing things, but looking back, it was a manufactured swing, one which I was able to do because I had really good mechanical control over my eyes, and could
flick them with a lot of agility.. at the time I didn't realize that what was really needed was to move my point of attention, and let go of the eyes, from a mechanical standpoint. I found myself straining much less when I just forgot about the swing, and let what happens, happen, swing-wise.
At some point the saccades and microsaccades kind of start meshing together as the distance and frequency of each gets closer, so that makes it hard to count too.
Yes, exactly. The smallest scale of our voluntary saccades overlap the largest scale of involuntary microsaccades, so that even researchers cannot distinguish if it was voluntary, or involuntary... a gray area, where
they just have to discount the data. Our small, voluntary saccades ARE good training and rehearsal for the involuntary system. Assuming one can shift on that scale without straining.