[From Bill Powers (941129.0600 MST)]
Bruce Abbott (9411various) --
While we've been up to our elbows in details of modeling probabilities
and contingencies, we've sort of lost track of the big picture. It's
been interesting to work with E. coli, but a microbe that uses random
tumbling as a means of steering isn't the best example for seeing the
regularities -- and lack thereof -- in behavior.
The real problem with the concept of consequences selecting the behavior
that leads to them is that in general there is no one behavior that will
lead to them. Consequences are a joint function of behavior and
independent variations in the environment. The driver, the road, the
wind, and the car all contribute about equally to the forces that steer
the car. The consequence of keeping the car in its lane couldn't
"select" a steering action that will have that result, because there is
no such steering action. This simple fact, which is true of most
behavior, has been overlooked in our conversations lately.
The appearance that the same behavior produces the same consequence
results from careless observation. Skinner was not a careless observer:
he recognized the problem here, although he didn't have the answer. He
rejected stimulus-response theory because he saw that neither stimuli
nor responses repeat from one instance of a behavior to the next. The
nearest he could come to a solution was to state the problem: behavior
has to be defined in terms of _classes_ of actions, and those classes
can be defined only in terms of consequences. "Bar-pressing" behavior is
actually a large class of actions -- infinite, if you look closely
enough and think about it -- which are held together in our minds only
because they have a common consequence: the bar gets depressed. Bar-
pressing is not really an action. It's an outcome of actions, and the
real actions can vary all over the place.
That way of putting it doesn't reveal the real nature of the problem,
because it focuses on different actions that happen to have a similar
consequence. The rat can use its nose, paws, mouth, or rump to depress a
bar and can do so from an infinity of different postures and
orientations relative to the bar. But if this is all one gets from
Skinner's observation, the main point has been missed.
The main point is that in general it is _necessary_ to use different
behaviors if the same consequence is to be brought about. If a pigeon
happens to find itself to the right of the key when the discriminating
stimulus light comes on, its response must be to move to its left if
it's to peck on the key. Yet a few moments later it may find itself to
the left of the key, or in front of it, or ten inches away from the key,
or with its beak poised exactly over the key. Somehow the same
consequence, the application of a peck to the key, must select
_different_ actions by the organism under different conditions.
The discriminative stimulus seems to be one answer to that problem, if
we recognize that this stimulus is a perception experienced from the
point of view of the organism (and not an objective state of affairs).
Now we can see that each different starting situation amounts to a
different set of discriminative stimuli, which can lead to a whole
collection of different behaviors -- just the behaviors needed to
compensate for the changes signalled by the discriminative stimuli as
experienced from the point of view of the organism. All that's necessary
is for the organism to discover what action should go with each
different discriminative stimulus.
But now we come up against the core of the problem: there are few
situations in which discriminative stimuli exist for each possible
environmental disturbance that can alter the relationship between
behavior and a given consequence. In many cases where such stimuli seem
to exist, there's no way they can be quantitative enough to account for
the quantitative precision of the consequence. And consequences are
often repeated under novel conditions, where even if discriminative
stimuli of sufficient quantitative properties existed, there has never
been a previous experience with them to permit acquiring the necessary
instrumental behavior.
If every possible behavior that could lead to a given consequence were
signalled in a quantitative way by some environmental indicator, and if
the organism had experimented long enough to have acquired a three-term
contingency for each of millions of different situations, then the
concept of consequences selecting behavior might stand up in court. But
those prerequisites don't exist under most real circumstances.
The control experiments in the paper by Bourbon and me, _Models and
their Worlds_, were designed to violate, one at a time, the assumptions
behind the explanations above, and to show that consequences were,
nevertheless, under control by the organism.
Consider the pursuit tracking experiment. A target moves irregularly on
the screen, and the subject uses a control handle (or a mouse) to keep
the cursor as near to the target as possible.
The explanation offered by most behaviorists for this behavior is that
there is a visual stimulus on the screen, a consequence of behavior,
that selects the handle movements which produce that consequence.
Eventually, this consequence (also playing the role of a discriminative
stimulus) is usually defined as the relationship between the cursor and
the target. If the cursor is to the left of the target, the required
behavior is to move the cursor to the right, and so forth. This seems to
fit the behavior very well.
But then we introduce a disturbance which adds to the effect of the
handle position on the cursor position. This disturbance is derived from
a random number generator, successive values being smoothed to limit the
bandwidth to about 0.1 Hz. There is no indication on the screen of the
magnitude of the disturbance. All that the subject knows is that the
cursor no longer faithfully follows the movements of the handle. Even
with the handle held still, the cursor wanders in a random pattern on
the screen.
Now there is no way for the consequence of the behavior, the cursor
remaining near the target, to select the pattern of behavior that will
create that consequence. Sometimes when the cursor is left of the
target, the subject is moving the handle to the left. There is no
discriminative stimulus to indicate what behavior is appropriate. The
random disturbance pattern never repeats, over hundreds of experimental
runs, so there is no pattern to learn. Yet what we see is that the
cursor follows the target very closely on the screen. Because the cursor
follows the target so closely, there is nothing in its pattern of
movement to indicate the magnitude of or pattern of the disturbance,
which follows an entirely different pattern. Yet we see the handle
movements reflecting the magnitude of the disturbance at every moment,
plus enough more movement to keep the cursor near the target.
I would like to see us turn from E. coli to these tracking experiments.
Behaviorists have offered explanations of them before, but you are the
very first behaviorist I have encountered in 20 years of arguing with
them who understood anything about simulations, and if behaviorism has
any defense against the phenomena to be found in these experiments, you
are the one to find it (you and Sam Saunders, who seems to have
disappeared). We have over a month before your animal studies can
commence. I'd like to see us spend at least a week or two on the
tracking experiments, to see whether any competing model can reproduce
the results as well as the control model does. If there is any way to
refute the succession of arguments above, we should find out about it.
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Best to all,
Bill P.