[From Rick Marken (950305.2000)]
Bill Powers (950403.1705 MST) --
Bruce has brought up the subject of "discriminative stimuli." I think
we should try to investigate it.
The data we would want to collect would be the process of acquiring
and giving up control after the signal.
I think we want to minimize the problem of visually switching from
one task to another, because the time taken to bring the new task to
the center of vision will add to any higher-level processing time we
Then why not do the "polarity reversal" experiment but signal the
reversal by changing the color of the cursor; red equals polarity 1,
green equals polarity 2. This way we always use the same cursor so
it's always at the center of vision.
Can we think of a higher-level goal, such as a score, that will
encourage doing as well as possible at whichever task is activated?
In the polarity reversal task the subject is always controlling the same
higher level goal (cursor on target) so this would not be a problem.
How does this sound so far?
So far, so good.
I've been thinking about this problem (the PCT apporach to discriminative
stimuli and "stimulus control") myself. I would like to demonstrate to
behaviorists what control of a complex variable (like the logical
relationship involved in "stimulus control") looks like. I made a start
at such a demo with my "program control" task where a subject uses a non-
programmatic output to control a program perception.
I think control of a logical relationship looks like "stimulus control" to
behaviorists because the actions that preserve the relationship are "part of"
the relationship. The bird, for example, must peck after the red light and
circle after green to maintain the relationship; pecking and circling are
part of the relationship. Suppose, however, that the bird could control this
relationship without its own actions being part of it; for exmaple, the bird
might be able to do something like what the subjects could do in the program
control task; the bird could peck (to restore the relationship) when the
relationship was NOT occurring and stop pecking when it was. If, for example,
the bird saw a red light but no subsequent peck (by a robot bird?), it would
peck a key; if it saw a green light and no subsequent circling (by the
robot bird) it would also peck. Of course, if the bird maintained the
relationship (by pecking ONLY at the appropriate times -- when the
relationship was not happening) it would get its "reinforcement", otherwise
not. (Rather than using robot birds to do the pecking and circling part of
the relationship, it would be logically equivalent to require that a
particular picture occur after the red light and another picture after the
This demonstration would at least show that the bird can control a logical
relationship even when it's own reponses are not part of the relationship. Of
course, if the bird cannot control the relationship in this way if would be
evidence that it is not controlling this relationship in the "stimulus
control" situation. That is, it would suggest that the discriminative stimuli
(red and green lights) really are causing the pecking and circling responses.
Martin Taylor (950304 18:00) --
The outside observer can determine the "information about;" the
control system only uses it.
But you have never shown that the control system uses "information about";
you just say it does. An outside observer can also determine the Laplace
transform of the perceptual signal, for example. Does that mean that the
control system uses this transform too? In fact, a control system uses the
difference between two signals (p and r) to continuously drive it's output.
Why don't we leave it at that?