From: piggy@gargoyle.uchicago.edu (La Monte Yarroll)
Subject: Re: TECH: Use of EMG as input to VR systems?
Originator: hlab@milton.u.washington.edu
Organization: University of Chicago Computing Organizations
Date: Fri, 4 Sep 1992 21:36:05 GMT



In <1992Sep4.123814.54182@qut.edu.au> barker@qut.edu.au writes:

> G'Day Netters,
> ...
> Just wondering if any has used EMG signals (monitoring of electrical
> signal produced by active muscles) as inputs to their VR systems.
> ...

For about a year I've been engaged in informal research into using
SMUT (Single Motor Unit Training) for computer input.

The primary observation is that humans can be trained to fire
individual motor units under volition.  The motor units can be turned
on and off, and thier firing rate can be varied.

There are about 500 accessable and trainable SMU's on your average
graduate student.  This suggests a potential for a human to computer
bandwidth which far exceeds any other method.

GEE WHIZZ PART

Once I've got the basic hardware working, I've got to come up with
ways to turn this into real computer controls.  My current model is
based on a set of 6 SMU's arranged in a cube of 3 opposing pairs.
This virtual 3d cursor could be used directly, or constrained so as to
simulate a limb.

One problem of interest to me is the problem of using this technology
for textual input.  My preliminary approach is based on a single key
keyboard I built called the "data potato".  The data potato used a set
of six switchs in a cube (familiar? :-) to detect the position of the
single key.  The key could move within a 3X3X3 cube, with the center
and neutral.  This is large enough to encode the entire Latin
alphabet.  On the mechanical model I built I was able to type about
10wpm after only a couple hours practice--pretty good for 1 finger.

The disadvantage of a virtual data potato is that it really fails to
exploit the full flexibility of a set of SMU's.  All it cares about is
"which SMU's are firing?".  But the SMU's also have a controllable
firing rate which is essentially ignored here.

The potential for musical inputs seems quite clear--music deals much
more with continously variable quantities which could be naturally
controlled with an SMU.

Once I get this far, I plan to work with David Stampe's REND386.

(If you're not interested in the details of my SMU research, you can
safely stop here.)

RESEARCH SUMMARY

A lot of work was done in this field about 15 years ago by Basmajian
and others.  As near as I can tell, interest in SMUT among
electromyorgaphical researchers has largely been replaced with using
SMU action potentials as indicators of other phenomena.  The
prosthetics people do not appear to be using SMUs--they concentrate
mainly in using large groups of motor units.  If anyone knows of
somebody currently working with SMUT, I'd love to know.

So far, I've got a simple amplifier and exectrode system which has
allowed me to isolate and control SMU's in my bicep, tricep and some
muscles of the hand.  I've also had success with teaching two other
subjects control of SMU's.

I brought a mockup of my front-end processor to SIGGRAPH which some of
you may have seen.  I've written several algorithms for recognizing
SMU's based on hardware described in the literature, but I've still
not got any real digitized data to work with.  The front end processor
I have is a 68HC11 Forth board from New Micros Inc, of Dallas, Texas.
For $75 it was the cheapest microcontroller with an ADC that I could
find.

My next tiny step is to build a low noise amp that will give me a good
clean signal in the 0-5v range.

This project is on hold for a bit while we prepare for our new baby
and our move to Tasmania.  With any luck, I'll be able to get some
real data within a few months.  If there's interest, I'll post a
followup when I've got more results.  If you want more details
(references, experimental setups, etc...) drop me a note at home:
<piggy@baqaqi.chi.il.us>.

La Monte H. Yarroll     Preferred:      piggy@gargoyle.uchicago.edu
   Work: piggy@mwc.com  Home:           piggy@baqaqi.chi.il.us
                        often:          postmaster@clout.chi.il.us
Newsgroups: sci.virtual-worlds