Arm "Ballistics"

[from Gary Cziko 920527.0845]

To Bill Powers & Greg Williams:

The arm demo sounds like it has the potential to stir up lots of problems
for the motor control people. I'm anxious to get this on the fileserver so
CSGnetters can play with it.

It just so happens I've been looking at the "manual control" chapter of a
text on engineering psychology (Wickens, 1992, who just happens to be the
advisor of the psychology grad student living next door). Research on
"discrete movement" is reviewed concerning a stylus in the hand which is
moved from a start to a target. As Wickens summarizes (pp. 448-449):

"Two important characteristics of this pattern are apparent: (1) The
general form of the movement is that of an exponential approach to the
taret, with an initial high-velocity approach followed by a smooth, final,
"homing" phase. In the earliest research in this area, Woodworth (1899)
distinguished between these two phases, labeling the first the _initial
ballistic_ and the second _current control_. (2) The velocity profile of
the movement shown in Figure 11.3b reveals that control is not continuous
but appears to consist of a number of discrete corrections, each involving
an acceleration and a deceleration."

So, two questions come to mind: (1) is this an accurate description of the
movement involved? and (2) if so, does the Arm demo behave similarly?

By the way, I've come up with what I feel is neat little demo of the closed
loop nature of apparently open-loop behaviors. I'll show it at Durango. I
wonder if anybody else has thought of pulling on elastic bands attached to
Michael Jordan's wrists as he makes a shot at the basket (maybe the Knicks
should have tried this; they tried just about everything else).


Wickens, C D. (1992). _Engineering psychology and human performance_. (2nd
ed.). New York: Harper Collins.


Gary A. Cziko Telephone: (217) 333-4382
Educational Psychology FAX: (217) 244-0538
University of Illinois E-mail:
1310 S. Sixth Street Radio: N9MJZ
210 Education Building
Champaign, Illinois 61820-6990