Competing "retrieval" rule vs compiled "habit" rule?

[Richard M Young]

I have what I think is a technical "how to" query about ACT-R, although it
sometimes turns out that what I think are "how to" issues are really deep
architectural ones.

Because I'm a bit confused, the question will be a bit muddled, so I'd
better explain the context.  I have been supervising a student project
which is to re-implement the Byrne & Bovair 3CAPS model of "post-completion
errors" (PCEs) in a way natural to ACT-R.  PCEs occur when the final step
of some procedure is to be taken after its main goal has been achieved, in
which case the final step has a tendency to be forgotten.  A classic
example is making 2 photocopies of a document but leaving the original on
the copier.  All great fun, but raising some issues that I'm finding tricky.

The particular aspect I'm finding difficult is capturing the effect of WM
load.  The data on PCEs, although sparse, suggest that the error is more
likely to occur under WM stress -- essentially you get distracted.  My
problem is that if one models PCE as arising from production competition
(with noise), then conflict resolution between productions is NOT sensitive
to WM, i.e. to declarative item activation -- only to the E=PG-C on the
competing rules.

(I had better say that my framework for thinking about this problem is
ACT-R 4.0, not 5.0.  I have no objection to 5.0, but I teach 4.0 because it
links with the 1998 textbook.)

Imagine this scenario, which is not a PCE but more like a prospective
memory task, but I think will make the point.  Suppose you drive home on a
regular route, so we assume (at least, I assume) that the decision-making
productions for driving that route are all compiled into productions, i.e.
"habit" productions.  (That would happen automatically in 5.0, yes?)
Suppose on a particular day that you are meant to stop at the bread shop
and buy some bread.  So (a) you say to yourself "Must stop at bread shop,
must stop at bread shop, ..." and with any luck, when you see the shop you
stop and buy some bread.  We might also believe (b) that if you were
listening to the radio at that point and got interested in one of the news
items, or if you were engaged in conversation with a passenger, or if some
interesting outside event happened at that point on the drive, then the
"must buy bread" would slip your mind (i.e. WM loss), and you are more
likely to forget to stop and buy.

How does this map into ACT-R?  In scenario (a), we presumably have
competition between, on the one hand, a compiled "habit" rule saying
essentially "at this point, keep on driving", and on the other hand, an
"interpretative" rule saying something like "if you have an intention in
mind and the time is right, then do it".  Now, I'm already uncomfortable
with the idea of competition between those two rules.  The *interpretative*
rule is presumably a very general one, with a long history of being applied
to totally different tasks in totally different circumstances, so I find it
difficult to make sense of that rule competing with a very specific "habit"
rule on the grounds of their respective statistical histories -- it seems
like comparing chalk and cheese.

Worse, that rule conflict is not, according to ACT-R, in any way sensitive
to the activation level of the declarative items that the interpretative
rule must retrieve.  (True, if the activation is below threshold then the
interpretative rule will fail, but that seems a very crude mechanism, and
also *assumes* that the interpretative rule will necessarily win the
conflict resolution.)  So the outcome is unaffected by whether you're
firmly saying to yourself "stop and buy bread" or whether that has slipped
your mind.  And that seems to contradict both data and also common sense.

Can anyone unmuddle me about this?

I'm also struck by the fact that there are no "retrieval" productions in
5.0, as I understand it.  Does this make a difference to the problem?

-- Richard