PCT Operant Project

[From Bruce Abbott (941026.1250 EST)]

Bill Powers (941025.1235 MDT)

Your derivation of my equation for VId is correct. In modeling the
environmental "feedback function," I would prefer it to yours if only because
it is easier to work with and understand.

Simply mentioning these things is not the same as calculating their
expected effects on the outcome of the experiment. Listing the
conditions rather leaves it up to the reader to decide whether they
deviated from standard conditions, and whether any deviations that exist
are important.

I don't wish to continue this line of argument further than this as I
essentially agree with you. But your earlier assertion was to the effect that
these things are not even mentioned, and it is to that assertion that I
responded. No observations are made theory free--what is assumed to be
important determines what is observed and reported. When I read the Method
sections of EAB research, I usually know what conditions are standard in these
studies, because I am familiar with the literature. The test of whether the
researcher has reported the important conditions under which a study was
conducted is whether others are able to replicate the results. In most EAB
studies they are. I conclude that the reporting of these conditions generally
has been adequate given the paradigm under which the data were collected and
interpreted. Your characterization made it appear that EAB researchers have
been sloppy and careless in describing their studies, and it is to this
implication that my reply was directed. EAB researchers reading that
paragraph would, I believe, feel unfairly attacked. I know I did.

From a different theoretical perspective such as PCT a whole different set of

considerations enters in which makes the existing EAB literature frustrating
to read, because the conditions and variables considered important from that
perspective are often missing from the published reports. I agree with you
entirely on this point, and that perhaps is the important thing.

I have a personal objection, as well as technical objections, to
reducing animals to 80% of their ad libitum weight, which can be
overcome only by showing a compelling need for this kind of treatment.

I had started to describe the program I had in mind, which included allowing
the animals to satiate while performing on the target schedule, but decided to
wait for a later post to get into those details. I think it would be
necessary to begin at some level of deprivation in order to speed up
acquisition of the lever-pressing response and get through the transient
reorganization phase, at least on initial studies. Regarding the 80% value,
your analogy to a human being brought to 80% free feeding weight does not
provide an especially valid comparison, as laboratory rats on ad libitum food
tend to be overweight because food can then be obtained with little
expenditure of effort, in contrast to conditions existing in the wild. The
80% value is used because higher values tend to produce less stable

A more "natural" way to proceed from the PCT viewpoint would be to provide
opportunities for feeding continuously, as you mentioned, and let the rat
decide. Studies of meal patterning in rats indicate that they tend to feed
throughout the day in small "bouts," and so I would expect to observe bouts of
lever-pressing distributed in this way.

A technical problem for me is how to gather data concerning what the rat is
doing throughout the study in addition to lever pressing. I may have to
resort to some kind of sampling procedure for some behaviors. What do you
think needs to be recorded?

I hope you will have some way of recording the quantity of reinforcer
ingested, instead of just how many accesses were given. A detailed
record would be best, but even a daily estimate of consumption would be
better than no information at all. If amount consumed varies on a short
time-scale, but we treat it as a constant, there will be variations in
the behavior (according to the PCT model) that will add unnecessary
noise to the results.

Determining amount of food consumed should not present a problem as the feeder
dispenses food in standard-size pellets. Although consuming them involves a
certain amount of waste, it is probably fairly constant and could be
determined with some precision by weighing what falls beneath the grid floor.

Would you be willing to start out with a simple full-time FR experiment
in which the ratio is varied from day to day within a range that keeps
the animal's weight at 98% of ad libitum or greater? Let's talk about

Yes. But I'm going to have to build different accommodations for our subjects
to allow them to occupy the experimental chamber full time. We'll have to
provide water as well as food (and measure consumption of both), which will
certainly change the nature of the results (i.e., schedule-induced
polydipsia). I'm wondering if that does not introduce needless complications.
At any rate, it's something we need to work out.

By the way, may I have your phone number?