Laurence,
That was nicely put. However, I don't think you resolve
the answer to your own question:
> Now it might be argued that this conversion of position from one
> reference frame (the retina) to another (eg. the body or shooting
> arm) is irrelevant since the system COULD solve the problem entirely
> visually.
Your answer,
> tiny errors are highly significant and
> they could easily arise by adaptation of any of the sensory systems
> involved in the loop between the target being seen and the bullet
> arriving.
doesn't really address the issue; if you can solve the problem entirely
visually, then eye,
there's no need to worry about
adaptation; your feet could be pointing 90 degrees to the target
and it would have no effect on targeting.
then you need to hold your body still (since body movement
may transfer to the rifle), but
I don't know much about rifles; do they have one sight or two?
If only a single sight, then I presume a shooter must line up
her sighting eye directly above the rifle, so that the line
between her eye and the sight is identical to the path the
bullet will take. If my presumption is correct (that rifles
have only a single sight), eye position in the orbit
and head position relative to the shoulder would be critical,
and your argument for working in short segments to prevent
adaptation would apply. Though from the torso down,
knowledge of body position would be irrelevant. (Though of
course one needs to stand perfectly still.)
Larry
-- Lawrence H. Snyder, MD PhD larry@eye-hand.wustl.edu Assistant Professor, McDonnell Center for Higher Brain Function Washington Univ School of Medicine 314 747 3530 (office) Dept of Anatomy and Neurobiology, Box 8108 4095 (lab) 660 South Euclid Avenue, St. Louis, MO 63110 3436 (fax)