[From Bruce Abbott (980614.1450 EST)]
Rick Marken (980614.0940) --
Bruce Abbott (980614.0750 EST)
There is still some question about whether rats can actually control
reinforcement _at all_ in the typical operant situation? Hmmm. I
wonder how they manage to get that pellet to fall into the cup,
then. . . .
Rats _cause_ the pellets to fall by pressing the bar. But based on
your own findings (that the rats produce maximum output regardless
of reinforcement ratio) it looks like they don't _control_ anything
about the pellets. Control (as you may recall) involves _varying_
output to protect a controlled variable from the effects disturbances
and (as in the case of the ratio schedule) changes in the feedback
function relating output to input.
Well Rick, let me see: If there is no pellet available in the chamber, the
rat presses the lever to obtain one. When the rat consumes the pellet (the
result of the action of another control system), this disturbs the variable
"pellet availability" from its reference value of "available." To correct
the error, the rat presses the lever, which restores the variable to the
"pellet present" reference state. Sounds like the rat is controlling
something about the pellet (its availability) to me. Wow, me arguing that
it's control and you arguing that it's S-R. Now _there's_ irony for you.
The phenomenon Chris refers to is called "ratio strain." It is
indeed a species of "giving up" and thus might qualify for the
"universal error curve" explanation, but there is good reason to
believe that it has another cause. If the animal receives _all_
its food by earning it in the chamber (rather than receiving
supplemental feeding in the home cage after the experimental
session), ratio strain disappears.
I don't understand the "good reason" to suspect that something
like the universal error curve is not involved. The "ratio strain"
still occurs when there is supplemental feeding in the home cage.
Why?
The point was that is _only_ occurs when there is supplemental feeding in
the home cage, not that it "still occurs" then. When there is no
supplemental feeding, rats continue to press that lever at ratios as high as
1500 lever-presses per pellet (highest tested). Without supplemental
feeding, the rats experience even higher error in their nutrient control
systems than they do when they get supplemental feeding. The universal
error curve hypothesis would predict that, if anything, the rats should be
even _less_ willing to press that lever in the non-supplemental feeding
condition than they are in the supplemental feeding condition, but in
reality the exact opposite is true.
When they were then placed in the tank immediately after the trim,
they suffered a severe "parasympathetic rebound," which stopped
their hearts.
Ah. The "trim" _caused_ a "parasympathetic rebound" that _caused_
a heart attack. Nice to see that our PCT man in Indiana is still
on the job;-)
As you know, Rick, disturbances to a controlled variable constitute one of
two truly independent variables or "causes" acting on a standard PCT-type
control system. If disturbances are strong and act quickly relative to the
response time of the control system, one can observe strong "reactions" on
the part of the control system which themselves have the effects of
disturbances to the system. The physician's tap to the patellar tendon just
above the kneecap provides a well-known example: the tap stretches the
muscle attached to the tendon, moving its length away from reference; the
sudden error triggers a strong contraction of the muscle that normally would
act to counteract the effect of the disturbance, but by the time the muscle
contracts, the initiating disturbance force is gone. With nothing to oppose
it, the muscle strongly contracts, carrying the leg upward: the "knee-jerk"
reflex. Parasympathetic rebound constitutes a similar phenomenon involving
the sudden disappearance of a disturbance which the autonomic nervous system
was acting to oppose.
So you see, Rick, I'm not talking lineal cause-and-effect here, but the
behavior (and failure) of a complex control system under strong and rapidly
changing disturbance.
Regards,
Bruce