From: billon@chopin.udel.edu (John Billon)
Subject: balance and vision
Date: 3 Jun 91 18:41:31 GMT
Organization: University of Delaware




Dear Sirs:

	I'm interested in how Human vision affects human "standing 
still" balance. VR technology seems like a good medium to use to get at 
the roots of the issue.  

	
	But first here is the  problem in greater detail. For one, 
people don't stand still, they have a kind of subtle rhythmic trajectory 
that they travel through, when they try to stand still. This can be 
illustrated if you stand very close, with the side of your arm just 
lightly touching a door-frame. So there is an orbit, a trajectory, that 
is a solution to a set of equations that describe an 80% water-filled 
structure with  an incredible number of degrees of freedom standing 
upright. I am curious about what are these solutions and how do they 
relate to all manner of things.

1)      Are they related to a person's psychological state of mind?
	Clearly when people are extraordinarily depressed, they don't
	stand the same way as when they are alert and keenly happy,
	their necks tend to go forward a bit more, their shoulders 
	droop... etc. When someone is happy, it must be expected 
	that they would respond to such perturbations in a very different 
	manner. 

2) Related to 1), When people age, how are these solutions affected? 
	When people are very young, how do they re-orient
	themselves when their balance naturally goes 
	through it's periodic trajectory? 

3) Now, why I'd like a real-time 3-space tracker, that I thought I could
	make out of a video camera, perhaps taking care of the problem of 
	too much information coming in by only accessing 1 or two of the 
	camera output lines:
	
		a) How is a person's balancing trajectory influenced by 
		a person's vision? For instance, suppose someone is out 
		on the outskirts of where there brain beleives they are
		vertical, say, if standing vertical  is 0 degrees, 
		and a person's balance trajectory is bounded by 
		plus or minus .25 degrees from vertical, and they're at .25 
		degrees, and their eyes are made to beleive that they're
		 at -.05 degrees, how will the trajectory respond?
                Can a person be  made to fall over?
	
		This is vaguely related to having some independent 
		control over the inputs in the pole-balancing problem. 
		Some control over how, for instance, velocity is input
		to the control system might be a good illustration 
		of this kind of idea. Very minor alterations would 
		probably make the pole completely un-balanceable, 
		if it had already been trained without such alterations.  

4) What is the outer limit of how a person's standing balance trajectories 
	can be altered? Would a person's mood be affected by an altered 
	balance trajectory?

	So, now that I've told you what  I really want to study,do any of you 
in VR-land have any advice? VR technology seems to be the closest thing that 
would be applicable to my interests. I have vague hopes of someday 
taking apart a data-glove or polhemus and using them as body-trackers
and trying to play with peoples' balance using nonlinear feedback.  
I've found a few books in the library about muscle systems and rhythmic motion 
that seem to be vaguely related to what I want to study.  Are there any
labs out there  working on the questions I have outlined above? Does anyone 
know of any papers in relevant fields that might be of interest to me?

	It would really be best if any replies could be emailed back to 
me directly.

					Thanks Alot!
					
					John