Applied PCT? + Angular Displacement

[From Fred Nickols (2003.05.13.0825)] --

I've been letting this sink in before responding so my apologies for any
perceived unusual delay.

Bill Powers (2003.05.10;-0857 MDT)]

Fred Nickols (2003.05.10.0545 EDT) --


In the pursuit-tracking experiments, the control system model represents
the task as that of controlling the distance between a cursor and a target,
with the reference-distance normally being zero. The following assumptions
are made:

Interesting. I would not have thought to word it that way. I've always
thought of the tracking experiment as essentially a matter of "keeping the
cursor on top of the target"

Yes, and this is how they still say it in engineering psychology. The way
they model it is to call the target the reference (signal), and say that it
is the error signal that the subject in the experiment perceives. I trust
that it seems strange to you to put the reference signal and conmparator in
the environment instead of in the brain.

Actually, that thought hadn't occurred to me but, now that you mention it,
it does. The reference signal, the error signal, the comparator, the
perception -- all are internal to the subject.

> .... This would suggest to me that when the experimenter tells the
subject to keep >the cursor one inch to the right of the target that the
"task" shifts from keeping >cursor and target aligned (i.e., the one on top
of the other and a distance of zero)
>to maintaining some kind of relative position between the two.

I agree that this is what would have to be done if we said that the
reference position was set by the target.

I'm not sure I get this. I buy the notion that the reference signal exists
in the subject and, as you say in the following, that no important shift
occurs in the subject's organization. But what you say below seems to rule
out any effect of angular displacement. Right or left are handled by
positive or negative numbers and so, presumably, are above and below but
what about keeping the cursor one inch from the target and at an angle of
45 degrees? How does that reduce to a distance only reference
signal? That's what I don't understand.

The rest of your response I think I get (but that could be unwarranted
optimism on my part).


Fred Nickols