Stimulus Control

[From Rick Marken (950306.1430)]

Bruce Abbott (950306.1505 EST) --

But aren't the keypecking and turning perceptual control systems
preorganized lower-level systems?


And by manipulating the references in this way, isn't one system being, in a
sense, "activated" in the service of the food-magazine perceptual control
system while the other one is put on hold (although, again, both systems are
active all the time in that both are constantly perceiving and controlling
their respective perceptions)?

There are ways to activate and deactivate control loops by setting reference
signals. It can also be done by putting a nonlinearity in the comparator
(once the error gets "too big" it returns to zero). In both cases,
"deactivating" the control loop means that there is no change in the control
system's output despite changes in its perceptual input; the control system
doesn't control. In my hierarchical model, manipulation of references
doesn't deactivate control systems in this way (even when the reference is
set to zero) because the control systems are always acting to make their
perceptions match their reference inputs; they are always controlling.

We might actually need to include a means of activating and deactivating
control loops in order to model "stimulus control"; if so, our model of
stimulus control will not be like the model of control of logical variables
in my spreadsheet hierarchy.

A pigeon has been trained to peck while a vertical line is projected on the
key and not to peck when a horizontal line is projected there. What happens
at the logic level when a line at 45 degrees is projected?

In my spreadsheet hierarchy it would depend on how the percpetual functions
at the logic level are constructed and how they are connected to the lower
level systems.

What the pigeon actually DOES (at least initially) is peck at an
intermediate rate. Does the logic-level system try to set positive
references to TWO lower-level systems (keypeck rate and, say "exploration"?

We'll have to model it; there are probably various ways.

Or should one conceive of the logic-level system as setting a single
reference (to keypeck rate) to positive or zero depending on the S-D?

I think this is right; probably two higher level systems setting the
reference for one lower level (keypeck rate) system. Of course, this setting
would be done on the basis of the deviation between higher level perceptual
and reference signals, not on the S-D directly.

I think we would do well not to assume, simply because the discriminative
stimuli are presented at discrete values, that we are necessarily dealing
with a logic-level system.

I agree that we should not assume that we are dealing with a logic level
controlled variable in discriminative stimulus tasks; we should TEST this
hypothesis. But I don't think we have hypothesized that the controlled
variable is a logical variable because the stimuli are presented at discrete
values. We have hypothesized a logical controlled variable because we (the
observers) can see that a logical variable --(red AND peck) OR (green AND
circle) -- is apparently being maintained at "true". When we do the tracking
version of the discriminative stimulus experiment we will be able to test
hypotheses about the higher order perception that is actually under control.