[From Rick Marken (980610.1010)]
Bruce Abbott (980610.1000 EST)--
On what basis do you expect carryover to invalidate the
I suspect that a subject who has already had success in the small
disturbance condition might be more inclined to "stick it out" in
the large disturbance condition than a subject who starts in the
large disturbance condition. But I don't know. Maybe a within
subjects design could work.
As I'm sure you know, random assignment to treatments does not
"eliminate any possiblity of systematic effects of uncontrolled
Right. Should have said random assignment "reduces the possibility..."
The universal error curve predicts that subjects will quit
performing (controlling) when the error becomes too large.
Error in what?
In the subjects -- theoretical error.
You told your participants that they "should try to stay at
the task as long as possible, for the good of science." Why
should they quit just because they can't get the cursor to stay
over the target?
When the error reaches a certain point, further increases in error
lead to a _reduction_ in output. So when the error become large
enough the subject should just stop generating output.
Given your instructions, they will most likely try to control
something like "pleasing the experimenter," or "doing good for
science," and they could continue to do this 'till the cows come
According to my understanding of the universal error curve, when
the error becomes large enough the output goes to zero no matter
what. If you have a better suggestion about what the instructions
should be then please let me know.
Furthermore, whatever effect would be predicted under the
"universal error curve" hypothesis would also be predicted by
all other hypotheses under which participants would quit when
their efforts to control failed for too long, so the proposed
experiment has no power to discriminate among them.
I agree that this is a problem. The subjects could be quitting
because a higher level system changes the reference for the
tracking control system to zero. But at least this experiment
is a first step; the experiment is designed to get data on how
subjects behave when controlling at different levels of difficulty.
Once we see the results of this experiments we can design other
experiments that more precisely distinguish the alternative theories.
Isn't this the right way to do experimental psychology?
The best that your experiment can hope to accomplish (and I
seriously doubt that it would do even that, for the reasons
given above) is demonstrate the phenomenon;
Yes. Can you suggest a better experimental way to demonstrate the
I'm sure you would prefer to use a single-subject design to
answer this question (as would I), so you must have a very
good reason for choosing a group design instead.
Yes. I assume that different subjects have different points at
which they go into the "no output" regime. By testing many
subjects in each condition I hope to average out these between
subject differences to see the true effect of the independent
variable (disturbance size) on the dependent variable (time until
Apparently, you must believe that increasing the size of the
disturbance over time until the participant is no longer able to
control either would not result in the participant's giving up, or
that carryover from the weaker-disturbance values would confound
the results. Or maybe you have some other reason. The one I
currently favor is that you either cannot or do not wish to attempt
a serious answer and wish to deflect attention from this fact by
engaging me in a debate about group-based designs.
I am trying to design an experiment to test the idea that there
is a non-linear relationship between error and output (the
universal error curve) like this:
output | *
> * *
> * *
> * *
0 |* * * *
Why not just suggest better ways to test this theory (using
single subjects if you like) instead of just criticizing my
design? How would you test the universal error curve theory?
Richard S. Marken Phone or Fax: 310 474-0313
Life Learning Associates e-mail: email@example.com