# Schmidt quotes

**URL:** <http://discourse.iapct.org/t/schmidt-quotes/10233>\
**Category:** CSG1993\
**Created:** [January 19, 1993, 12:48pm UTC](http://discourse.iapct.org/t/schmidt-quotes/10233 "1993-01-19T12:48:00Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Hortideas\_Publishin1](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/h/f6c823/32.png) [@Hortideas\_Publishin1](http://discourse.iapct.org/u/Hortideas_Publishin1)\
**Post date:** [January 19, 1993, 12:48pm UTC](http://discourse.iapct.org/t/schmidt-quotes/10233/1 "1993-01-19T12:48:00Z")

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> From Greg Williams (30119)

The following excerpts are from Richard A. Schmidt, MOTOR CONTROL AND  
LEARNING: A BEHAVIORAL EMPHASIS, Human Kinetics Publishers, Champaign,  
Illinois, 1982 (dedicated to "former mentors" Jack A. Adams and Franklin M.  
Henry).

[diagram on page 204 shows "closed-loop model for movement control" with  
(surprise!) the reference signal and comparator inside the person]

205 - "The idea is that the system [diagrammed on page 204] can 'compute' the  
expected nature of... sensations in the form of a reference and can compare  
the feedback it receives on a particular trial with the feedback it expects to  
receive.... Closed-loop models... are thought of in essentially two ways.  
First, they provide a basis for knowing if a movement produced is correct or  
not.... A second way... concerns the control of ongoing movements..."

206 - "The closed-loop model... has been very effective and useful for certain  
kinds of responses.... the model seems to have considerable appeal for  
movements in which something is regulated at some constant value... These  
movements are called TRACKING responses... The most important generalization  
from... [tracking] research is that if the models are used in computer and/or  
mechanical SIMULATIONS of the human in which the computer or mechanical device  
is controlled in ways analogous to those in... [the diagram on page 204],  
these nonliving devices 'come alive' to behave in ways nearly  
indistinguishable from their human counterparts. By proper adjustment of  
certain mathematical or electronic elements in the devices (called  
parameters), the system can be made to show many human characteristics, and  
they track with essentially the same levels of error.... The large body of  
experimental literature suggests that because the human can be mimicked so  
well by computers that use closed-loop mechanisms such as shown in... [the  
diagram on page 204], the human in these [tracking] situations can be regarded  
as a closed-loop control system, responding essentially by analyzing the  
feedback produced against the reference of correctness and issuing  
corrections. The evidence does not prove that humans actually track this way,  
but the agreement between theoretical predictions and data is very strong, and  
alternative theories cannot boast of similar success."

210 - "Engineers can design robots and other machines to behave... using what  
they call POINT-TO-POINT COMPUTATION methods. The position of the limb at each  
point in space and at each time in the movement is represented by a reference  
for correctness, and the system can be made to track this set of positions  
across time to produce an action with a particular form. But the system must  
be very 'smart,' and it must process information very rapidly, even for the  
simplest of movements. All of these references for correctness must be stored  
somewhere, and each of the points will be different if the movement begins  
from a slightly different place or if it is to take a slightly different  
pathway through space.  
&nbsp;&nbsp;Engineers have generally found that these methods are very inefficient for  
machine (robot) control, which has led many motor behavior researchers (see  
Kelso, Holt, Kugler, & Turvey, [in G.E. Stelmach & J. Requin, eds., TUTORIALS  
IN MOTOR BEHAVIOR,] 1980; Kugler, Kelso, & Turvey, [in same,] 1980) away from  
these kinds of control processes to explain human skills....  
&nbsp;&nbsp;A compromise position is that only certain positions in the movements are  
represented by references of correctness. One viewpoint is that feedback from  
the movement when it is at its endpoint is checked against a reference for  
correctness and that subsequent corrections are initiated to move the limb to  
the proper position. These views of motor control hold that the limb is more  
or less 'thrown' in the direction of the endpoint by some kind of open-loop  
control and that then the limb 'homes in on' the target by closed-loop  
control."

211 - "... the information-processing mechanisms, which lie at the very heart  
of the closed-loop system shown... [on page 204], require a great deal of TIME  
AND ATTENTION for stimuli to be processed to yield a response.... with rapid  
actions sufficient time is not available for the system to (a) generate an  
error, (b) detect the error, (c) determine the correction, (d) initiate the  
correction, and (e) correct the movement before a rapid movement is completed.  
Muhammad Ali's left jab is a good example. The movement itself is about 40  
msec; yet, according to our estimates [made earlier in the book on the basis  
of movement-correction experiments], detecting an aiming error and correcting  
it during the same response should require about 150 to 200 msec -- the time  
necessary to complete the activities of the stages of information  
processing.... Another problem is that the time between two responses that are  
not grouped (see... [M.C. Smith, in W.G. Koster, ed., ATTENTION AND  
PERFORMANCE II, 1969]) was found to be essentially 190 msec. Therefore, the  
time between successive corrections (because corrections are responses) should  
be similarly separated. This information has serious consequences for models  
of human limb control that demand a large number of attention-based  
corrections in a very short period of time. Point-to-point computation models  
have this basic problem when human performance is considered."

212 - "What about the possibility that the central nervous system contains  
closed-loop mechanisms that do not require any attention?

215 - "... experiments like Dewhurst's ([IEEE TRANS. BIOMED. ENGR. 14, 167-  
171] 1967) show that corrections for suddenly presented changes in position  
can be initiated far more rapidly than the earlier 200-msec estimates, with  
correction latencies being from 30 to 80 msec in the various investigations  
that have been done. This kind of result suggests that the information-  
processing stages are not involved in these corrections, as the stages require  
too much time for processing."

243 - "On strict experimental grounds [deafferentation studies], the evidence  
does not really show that the [open-loop] response-chaining hypothesis is  
incorrect, although it strongly suggests it. A more reasonable hypothesis  
would be that feedback is not essential for the production of at least some  
movements, although it is likely that feedback provides increased flexibility  
and improved fine movement control. The possibility remains that under some  
conditions or for certain kinds of skills the response-chaining hypothesis  
might be correct, but it seems fair to say that it is not correct in general."

249 - "Henry and Harrison (PERCEPT. MOT. SKILLS 13, 351-354] 1961) asked  
subjects to begin with a finger on a key located by their hip and at a 'go'  
signal to move forward-upward to trip a string in front of their right  
shoulder. They were to do this as quickly as possible. The simple RT in this  
situation was 214 msec on the average, and the movement time was almost the  
same, at 199 msec. Sometimes a second light would come on indicating that the  
subject should avoid tripping the string or at least begin to slow the limb as  
quickly as possible. The 'stop' signal could come on at one of four points:  
110, 190, 270, and 350 msec after the 'go' signal....

250 - Henry and Harrison measured the time to begin to decelerate the limb  
after a 'stop' signal.  
&nbsp;&nbsp;Their results are simple. Only when the 'stop' signal was given at the 110-  
msec location was there a tendency for the subjects to start to slow the  
movement before it had been completed. But the more interesting feature of  
these data is the subject's response in the 190-msec condition. Notice here  
that the 'stop' signal came on 24 msec BEFORE the movement even started, and  
yet the movement was carried out without interruption....  
&nbsp;&nbsp;If the information-processing stages are too slow to be involved in details  
of a particular action..., then the question is: What does produce these  
patterns of action? The best theory to have been proposed at this point is  
that these patterns are PREPROGRAMMED, structured in advance, and run off as a  
unit without much possibility of modification from events in the environment.  
To me, this is one of the strongest lines of evidence available that movements  
are controlled by motor programs."

There is more, but I'm tired of typing for now. If this is useful, let me know  
and I'll probably post another installment.

As ever,

Greg

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**Author:** ![bnhpct](http://discourse.iapct.org/user_avatar/discourse.iapct.org/bnhpct/32/34_2.png) [@bnhpct](http://discourse.iapct.org/u/bnhpct)\
**Post date:** [January 19, 1993, 2:08pm UTC](http://discourse.iapct.org/t/schmidt-quotes/10233/2 "1993-01-19T14:08:14Z")

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[From: Bruce Nevin (Tue 930119 08:44:23)]

(Greg Williams (30119) ) --

Controlling for the stop signal I assume is at a higher level of  
the hierarchy, and the delay corresponds to that in the portable  
demo described in BCP (extended arm is raised before lowering it  
in response to signal).

Isn't some of their time problem due to thinking of the loop  
sequentially (trial and then error and then correction in another  
trial) rather than concurrently and continuously?

> **···**
>
> -=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-=+=-
> 
> Yet Another Tack (YAT) department: "hard science" fiction  
> stories as I recall have some legitimate scientific or  
> engineering premise on which the plot of the story is made to  
> hinge. Clever protagonist saves day by applying scientific  
> principle in an ingenious way, explained in denoument much as the  
> interlocking of clues is explained at the close of a mystery  
> story. Imagine the Uptown administrator of the project rejecting  
> the proposed solution on basis, say, of Ashby's Law of Requisite  
> Variety, and having his fat pulled out of the fire by our  
> intrepid underling from the ghetto. Could even have the premise  
> obdurately reinterpreted those who still don't get it (e.g. Mr.  
> Uptown), and this commented on by the New Convert (gotta have  
> someone to carry the "aha!" for the reader) in a closing  
> conversation with Our Hero. You said you like fables, Rick?  
> Poul Andersen did this sort of thing with a General Semantics  
> premise in the early '50s (\_The World of Null-A\_ f'rinstance).
> 
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Bruce  
> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[bn@bbn.com](mailto:bn@bbn.com)