[From Bruce Abbott (980316.1245 EST)]
Bill Powers (980314.0515 MST) --
Bruce Abbott (980313.2215 EST)
Also, bear in mind that rats are nocturnal and on this ground would be
expected a priori to prefer a dark chamber over an illuminated one.
Associating the signaled condition with houselight-on would bias the outcome
against preference for the signaled condition.
Was there any sign of this bias in the data?
Very little: Preference for the signaled over the unsignaled condition is
strong, tending to swamp out weaker preferences like those for darkness over
illumination.
However, the rats preferred the signaled condition either way.
It's difficult for me to accept that rats could understand a concept like
"signaled condition." I would keep looking for something that is different
between these two conditions, something that a rat incapable of verbal
generalizations might be able to perceive. For example, was there any
difference in the number of shocks received in the two conditions?
The number, intensity, duration, and distribution of shocks was identical in
the two conditions. The apparatus programmed the shocks independently of
conditions.
Bruce Nevin (980314.1607) --
Suppose the rats have some way to control the perception "no shock".
Suppose (for example) that the rats learn to jump off the conductive floor
a tad just as the tone ends and the shock happens. Or suppose they can
"steel" themselves to the shock, maybe make it less unpleasant by tensing
muscles in advance, but they have know when to do this.
This, in various versions, is called the preparation hypothesis.
Or suppose they
don't know when to relax and attend to other things without the tone as the
first part of a sequence, and they prefer to be able to relax and attend to
other things at least some of the time.
This is known as the safety-signal (or safety) analysis.
Barring some such means to control a perception something like "no shock"
or "relax and enjoy life", the inference Bruce A seems to be making is that
the rats control for knowing when a mild unpleasantness will happen, as
opposed to having it catch them unaware. Even this requires no perception
called "the signalled condition." There are two perceptions. One is the
sequence, 5-s tone ending with shock. The other is shock.
There are others. One is the houselight being on or off. In the case where
houselight-on was associated with the signaled condition, houselight-on plus
tone is associated with imminent shock, houslight-on by itself with absence
of shock, and houselight-off with some low (but non-zero) rate of shock
occurrence (120-s/shock on average).
After one minute the apparatus would disturb the CV again by automatically
switching the rat back to the unsignaled condition, and once again the rat
could counter the disturbance by pressing the lever and thereby returning to
I'm having trouble with the time specification here. After one minute? The
shocks are on average 2 minutes apart. How often would signalled shocks
ever occur within a 1-minute grace period? Is this a typo for 10 minutes,
or some other number greater than 2?
A single lever-press while in the unsignaled condition bought the rat one
minute of time in the signaled condition, with its associated state of the
houselight. Shocks were programmed on a variable-time schedule which
approximated a constant shock probability over time. Intervals between
shocks varied at random between an 8-s minimum to a mamimum of around 10
minutes. Thus there would have been many occasions when no shocks (or
signals) would occur during the 1-minute changeover period.
Thanks for describing this experiment. What explanation did you have at the
time? How has your understanding of PCT affected that explanation?
At the time we were evaluating several hypotheses, including the preparation
and safety hypotheses. According to the safety analysis, the rats changed
over from the unsignaled to the signaled shock condition because most often
this would result in an immediate transition from a stimulus associated with
a constant probability of shock (the stimulus identifying the unsignaled
condition) to one associated with a zero probability of shock (the stimulus
identifying the signaled condition, presented without the tone) and much
less often to a stimulus associated with shock (stimulus identifying the
signaled condition, plus tone). According the the preparation analysis,
rats changed over to the signaled condition so that they could execute
well-timed preparatory behaviors that would serve to minimize the perceptual
aversiveness of the shocks. Proposed behaviors included adopting a
particular posture on the grid, getting ready to spring off the grid and
thus minimize shock contact time or current flow, tensing muscles, and
releasing endorphines in the brain and/or spinal cord to produce a temporary
state of relative analgesia. There was also an information hypothesis,
which stated that rats have evolved a preference for having information
about biologically significant events (like the occurrence of food or of
danger) and will choose to have that information even when it is "bad news."
My understanding of PCT has not affected how I would go about explaining the
preference, but it does suggest alternative ways to conduct the
investigation which I would not have thought of otherwise.
Rick Marken (980315.1150) --
Anyway, as Bruce noted, he was doing this research to test for
controlled variables. That's why I [Rick Marken (980313.1050)]
expressed interest in hearing about the "subsequent research"
Bruce mentioned [Bruce Abbott (980313.1330 EST)] that attempted
to tease out...what the rats [were] really controlling for when
they acted so as to remain in the signaled rather than the
unsignalled schedule?"
Glad to hear that you're interested.
I imagine that this subsequent research involved systematically
disturbing other aspects of the "signaling" situation that the
rats could control. For example, they probably did studues where
the phase relationship between signals and shocks was disturbed.
The rats were presumably given a means to control this phase
relationship (for example, by pressing the bar faster or slower
they could advance or retard the phase).
Had I known more about the Test at the time, I might have conducted a study
very much like this, but alas, I didn't. What I did do might be considered
an alternative form of the Test. First, I established conditions under
which rats would immediately act to correct the disturbance (being switched
back into the unsignaled condition) by pressing the lever that returned them
into the signaled condition). Next, I systematically varied the parameters
and conditions of the signaled condition, looking for changes what would
destroy the rat's interest in correcting the disturbance. In other words, I
looked for features of the signaled condition which, when removed,
eliminated the rat's interest in controlling for being in the signaled
condition.
The rats must have
controlled for the signals occuring just before the shocks, since
Bruce A. told us that the rats were controlling for "signaling",
and Bruce A. wouldn't lie (like I do;-))
You are right about one thing: I don't lie. But speaking of lies, did not
say that the rats were controlling for "signaling." I said that the rats
controlled for being in the signaled, rather than the unsignaled, shock
condition, which is exactly what they did. After this had been demonstrated,
the next step was to identify what specific factors were responsible for the
rats' preference for the signaled over the unsignaled shock condition.
I'm sure there were a whole bunch of tests like this to determine
what the rats were controlling because, as Bruce A. said, he knew
how to test for controlled variables before he ever even heard of
PCT (and Bruce A. is an honorable man). This is great news because
I have been under the impression that "conventional" psychologists
have not been doing much testing for controlled variables. But,
apparently, some (like Bruce A.) have so now we will have many
examples of research aimed at testing for controlled variables.
I didn't know at the time that I was testing for controlled variables (From
my point of view I was testing for "preference"), but in retrospect I can
see that this is exactly what I was doing.
I'm really interested in hearing about the research that nailed
down what the rats in these "signaled shock" experiments are
controlling for, Bruce. Could you describe it for us? It would
sure make a great substantive contribution to the discussions
on the net.
Great! I've got quite a number of them. For starters, how about the one in
which I evaluated the version of the preparation hypothesis which says that
the rats use the signal to get set to hop off the grid floor, thereby
minimizing their contact with shock? For this study I designed and
constructed a piece of electronics which allowed me to record the pattern
and total duration of contact with each shock delivered. Each rat was
exposed to both the signaled and unsignaled shock conditions while that
pattern and duration of each shock was recorded. I also put together a
solenoid mechanism which tripped the shutter of a 35mm camera just at the
moment prior to shock delivery, in order to capture on film the rat's
posture on the grid.
It did turn out that the rats got into a particular posture during the
signal (they "froze," which is a species-typical response to certain signs
of possible danger), but in consequence they were slower to start running
when the shock began and thus received longer total contact with the grid
during the shock than when the shocks were delivered unsignaled. The rats
were actually receiving more total contact with shock when it was signaled
than when it was unsignaled.
This experiment ruled out differential grid contact as the explanation. An
earlier study had demonstrated that rats continued to prefer the signaled
shock condition when shocks delivered there were up to three times more
intense than those delivered in the unsignaled condition. Whatever it is
that the rats prefer about the signaled condition, it is powerful enough to
win out over even fairly strong preferences for weaker over stronger shock,
when these two factors are pitted against one another. If some other type
of preparatory response is at work, it would have to be extremely effective
to make these physically much stronger shocks seem weaker than those
physically weaker shocks of the unsignaled condition.
Regards,
Bruce