[From Bruce Abbott (941229.1530 EST)]
Bill Powers (941227.1500 MST)
Bill, your suggestion for encoding the operant data sounds like a good
approach; I'll work up a program for running the experiment within the next
few days.
Let's also be thinking about how to get a faster computer -- even a
486SX-25 would be something like 40 times as fast. Maybe we can take up
a collection.
The 8088 may not be as serious a limitation as it seems: I only run one
station per computer and have four IBM PC clones and stations available. In
the bad ol' days I used to run all stations simultaneously on a single PDP-8F
(all with a whopping 32K of magnetic core memory), but every time the computer
fried something (which was fairly often), the whole lab went down. In the
current setup, with each computer responsible only for one station, speed is
less critical and I lose only one station when something melts.
I don't know about using "access to reinforcement"
rather than just delivering pellets -- seems to me that the "access"
approach leaves the "rate of reinforcement" actually received pretty
fuzzy. But that's what Motheral did. I trust you'll be measuring
original quantities and spillage -- once or twice a day should be enough
to give reasonable estimates of actual consumption, pro-rated per
reinforcement.
The chambers are equipped with standard pellet feeders that deliver standard
45 mg pellets, so we needn't be concerned with "access to reinforcement" as in
the Motheral experiments. I'll keep track of any spillage, as we had
discussed earlier.
Rick Marken (941227.1630)
The operant research you are
planning with Bill will give us all an opportunity to see whether rats
are really controlled by food pellets or whether they are controlling
some perceptual characteristic of those pellets.
What, do you think there's any doubt? I'll bet on perceptual control. Now
what can I put you down for?
I think it would really
be neat if you include a variable disturbance in a least one of your
experimental conditions.
Yes, but that will have to wait until we gather the initial data on FR
schedule performance. Changing the ratio requirement is itself a form of
disturbance to which the rat must adjust. However, changing the ratio alters
several perceptual variables at once, including (a) the effort that must be
expended per pellet, (b) the count, i.e. number of presses per pellet
delivery, and (c) the delay to next pellet delivery. Ignoring the first two
variables, if we assume that the rat's reference level for delay to next
pellet delivery is around zero, one would expect that increasing the ratio
requirement should increase the response rate and decrease the time between
collection of a pellet and resumption of lever pressing.
But this is not what has been observed; rather, an increased ratio requirement
produces longer delays between pellet collection and lever-press resumption,
without much effect on the rate of responding maintained once pressing has
resumed. No doubt this occurs because rats have even more trouble
understanding PCT than I do and, of course, are strongly motivated to please
their Skinnerian masters by producing data consistent with reinforcement
theory. (;->
It seems reasonable that the rats would prefer immediate gratification (at
least Freud thought so), but there seem to be other forces at work.
Identifying the relevant perceptual variables and figuring out how the several
control systems involved interact to produce the observed changes will require
additional research. For example, it is possible to introduce the additional
delay to pellet delivery without changing the effort required or the count,
and to change the effort required without changing the count or the delay.
And that's just the beginning. Whoever said rats were simple?
Regards,
Bruce