[ACT-R-users] stopping pm

[Richard M Young]

Just a small comment on this matter of stopping Act-R models, from a 
*teaching* perspective.  I've just done my 2nd week class in my 
final-year undergraduate course on cognitive modelling, and we ran 
right into this issue of stopping.  Dan characterises well what seems 
to be the style in the Act-R tutorial material when he says:
>all that's really necessary is to just change the state so that none 
>of the productions will match

It can be fairly confusing for beginners as things stand.  The first 
model (count) finishes by setting the STATE attribute of the goal to 
STOP.  So of course the model stops.  Well, no, it's not that simple. 
I asked the class to see what happens if the rule is changed to set 
the STATE to FLUMMOX or virtually anything else, and of course it 
still stops.  In the second model (addition), considerable ingenuity 
is used to choose a stopping condition.  I don't have the model in 
front of me as I write, but it's something like setting the COUNT 
attribute to nil while leaving the SUM attribute non-nil, and it 
turns out that particular combination prevents any rule from firing.

Aside from being opaque and confusing to beginners, one of the 
problems with using this kind of ingenuity to stop the model is that 
it isn't stable over changes or additions to the model.  Make certain 
changes, and the model will no longer halt cleanly, or perhaps at all.

I agree with just about all the sentiments expressed in the discussion so far:
   - clean separation of model code from the environment code;
   - people don't actually "stop", so neither should Act-R;
   - but in practice, especially with small tutorial models, they
       can't be expected also to model Ss getting on with the rest
       of their lives.

I didn't know that the !stop! command still existed.  If it were 
renamed to be more suggestive of a "that's all for now folks" -- 
maybe !end-experiment!, or !resume-your-life! -- I would prefer it in 
the tutorial examples, despite the theoretical objections to the 
!syntax!.

Any chance of getting agreement on this, and getting the tutorial code changed?

Best,
-- Richard