From Greg Williams (930922 - 2)
Bill Powers (930922.0710 MDT)
1. "When driving an automobile, the HUMAN OPERATOR perceives a
discrepancy or error between the desired state of the vehicle
and its actual state. The car may have deviated from the center
of the lane or may be pointing in a direction away from the
road. The driver wishes to reduce this error."
This says explicitly that what the driver perceives is an error,
implying that the error exists outside the driver. If the error
exists outside the driver, then the comparison process must also
take place outside the driver, interpreting certain relationships
of the car to the road as errors and presenting this interpreted
result to the driver's senses.
It doesn't seem so explicit to me. Do you think also that the
quote implies that "wishes" are outside the driver?
In PCT, what is perceived is simply the relationship of car to
road that exists at any time. It is neither correct nor
incorrect; it is what it is. The perception of this relationship,
inside the driver, is compared with a reference signal, also
inside the driver. The driver can select any state of the
perceived relationship as a reference condition, and manipulate
the car to achieve the reference relationship -- for example, car
straddling the lane-separator line, car crosswise in the road,
car leaving the road altogether (as when turning a corner), car
crashing into a bridge abutment in a suicide attempt. What comes
in to the driver's senses is not an error signal, but simply a
report on the current state of affairs as the perceptual
equipment represents it. There are no errors or "discrepancies"
represented in the perception.
Why don't you or Gary Cziko ask Wickens (who is at UIUC) if he
disagrees with this model. I suspect that he doesn't have a
problem with it, and sees it as compatible with his quote above.
I'd be very interested in the comments of Hans Blom along these
lines, too.
2. (regarding tracking of time-varying inputs in general:) "It
is assumed that the human 'intends' to produce a given
position."
The implication here is that the intended position is the actual
position of the car relative to the actual road (etc.), outside
the driver. Putting "intends" in quotes suggests that the author
doesn't treat intention as a real phenomenon, but just as a way
of speaking. I don't see that Wickens has made it clear that an
intended position is an intended _perception_ of position, as
opposed to an actual position objectively defined. Nor is it
clear that Wickens identifies an intended position as an
adjustable reference signal inside the controlling system.
Again, why not ask him, rather than jumping to a conclusion when
the intended meaning isn't clear? You and I could argue ad
nauseum about the nuances of nonPCTers' comments, but why bother
when the sources of those comments are accessible?
Perhaps what we need is a survey of all the major manual control
experts' way of describing simple control situations, to get an
idea of how many understand that only perceptions can be
controlled, and that intentions and error signals exist inside
the driver.
An excellent idea, except that I would suggest that it should have
been done BEFORE jumping to conclusions about what you THINK the
manual control experts are doing.
From your citations from Wickens, I'd say he may understand
control theory but he flunks PCT, although perhaps he redeems
himself in other parts of the book.
Maybe so. Let's just try to preclude the possibility that YOU
understand PCT, but flunk manual control theory because you
haven't looked into it sufficiently. I think it is important that
PCTers not lose their credibility with control engineers, which
is likely if the control engineers believe that they are being
misconstrued by PCTers.
As ever,
Greg