Long Sunday Thoughts

[From Bruce Abbott (950115.1630 EST)]

Bill Powers (950115.0600 MST) --

John Gardner (950114.10:30 EST)

    BUT-- I have a two-link, two-motor direct-drive robot arm,
    controlled by a 486PC, programmed in "C" which is always looking
    for interesting experiments. The robot works in a horizontal
    plane, positioning it's end-effector (a plotter pen) in a circular
    workpace that's about .8 m in diameter (I use only one quadrant of
    the workspace....What makes it interesting is that the direct-drive
    nature of the robot makes the multi-body dynamic effects very
    significant. Decent control of this beast if very difficult.

Well, now, that's extremely interesting. The design is just what I would
have wanted as a real test of the arm model. I think that with a little
ingenuity we could simulate the properties of the human stretch-tendon
reflex and muscles closely enough to come up with a real test. How about
sending me the specs for the inputs to and sensory outputs from the arm?
I'll see if I can't work up at least a beginning design for you to fool
around with. I trust that there are signals indicating at least joint
angle for each joint.

The only thing I'm not sure of is whether we can get along without the
strain-gauge equivalent of the tendon reflex: a direct measure of the
torque applied to the joint. But maybe if the torque motors are fast
enough (torque proportional to driving signal at all speeds
encountered), we can fake that by using the driving output signal as if
it indicated torque directly. We can use the position feedback to
simulate the way the muscles work and get derivative and position
feedback too. It's sure worth a try!

    The bottom line is that I'd be interested in implementing a
    proposed control scheme and report the results.

You're on! Let's do it.

FANTASTIC! I was starting to worry that I was going to have to build the
damn thing myself.... Really, this is great news. Amazing where simply
asking a question can sometimes lead. Please keep us informed of the
progress on this project.

On a related topic, I recently saw a DONAHUE show featuring the work of a
prosthesis guy. One man on the show had lost both arms, one above the
elbow, when a cable he was installing made contact with over 14,000 volts.
The prosthetic arms were battery operated and activated by muscle potentials
being picked up from the upper arm. The system gave proportional control
over the elbow joint angle and finger grip pressure. Proprioceptive
feedback came from the muscles where the sensors were located, and they were
working on a model the transmitted hot and cold sensations from the "hand"
to the person's skin on the remaining part of the arm. When the guy said
that it costs over $20K just to manufacture the motorized ELBOW, I was
reminded of your $100K estimate to build Little Man. Sounds like you are
not too far off...

Mary recorded a PBS "Frontline" program on "facilitated communication"
with autistic children; I saw it last night. After spending half an hour
showing how beautifully it works, the program then turned to the
problems. The problems arose when all over the country, autistic
children were communicating that they had been sexually abused by
father, mother, sibling, grandfather, grandmother, teacher, and just
about everyone else. Children were being removed from their parents and
being put in foster care.

So a lawyer got a psychologist to think up a test to see who was
orginating the communications, and the psychologist came up with a
dilly. He showed one picture to the facilitator and another to the
autistic child. When both pictures showed the same object, the autistic
child and facilitator pecked out the keys on the alphabet board to
produce the right name of the object. When the objects were different,
however, the name that was written was the name of the object the
facilitator saw. In 180 trials where the pictures were different, there
was not a single instance of the "communicated" name being the object
the autistic child saw. This was repeated over and over; in all the
tests where the pictures were different, there was not a single instance
of the communicated word describing what the child saw. What was
communicated was ALWAYS what the facilitator saw.

I saw this myself some time ago, and was quite impressed with it. It
strongly reminded me of the old "Clever Hans" story, in which a retired
German mathematics professor had become convinced that his horse could
reason and even solve problems in arithmetic. In that case also, it was a
psychologist (Oskar Phungst) who showed that Hans "knew" the answer to a
question being posed to him only if his owner or the audience did AND the
horse could see them.

But speaking of autism, here in the department we have an associate faculty
member and full-time clinician with whom I was conversing a few days ago
about (what else?) PCT. I mentioned that it would be interesting to conduct
a study on autistic children to determine how their control systems differ
from those of more normal children, and suggested that the differences most
likely involve fairly high levels in the heirarchy. It turns out that the
guy works with autistic children in his practice and that there are
apparently defects in the low-level control systems as well. He became very
interested in what I had to say and asked about whether our library has a
copy of B:CP. I lent him my copy.

There may be a very nice opportunity here for some research, which would
apply the Test to determine what perceptions young autistic children control
as compared to non-autistic kids of the same age, and how well they are able
to do it. It also would be interesting, I think, to sit one of these
autistic kids down at a computer terminal and have him or her run through
some of the tracking tasks.

On THREECV1: Is there any particular reason why the participant is given
the opportunity to see and then accept or reject each set of stored
disturbances? If not, I'd just as soon have the program skip that part
during data collection.

P.S. I'm glad we're having fun now; it sure beats the alternative!

Regards,

Bruce