ACT-R 4.0b4

[Christian J Lebiere]

A new beta version, ACT-R 4.0b4, is available on the ACT-R web site:

http://act.psy.cmu.edu

It contains a number of changes from the previous release, all of them
cosmetic except for a relatively minor one.  We expect this to be the
last major batch of changes until the official release of ACT-R 4.0 next
year.

The one non-cosmetic change is that the cost parameters a and b are now
learned upon failure as well as success.  This seems to be the
mathematically correct thing to do.  Let us know if it significantly
affects your model.

The printing conventions have been refined.  Chunk types are printed in
upper case, the first letter of each word in chunk and production names
is capitalized, and all other values (e.g. nil) and variables are
printed in lower case.

The !output! command has been generalized to make the format string
optional.  It can now take either a single value, or a list of mixed
text and values.  See the factorial example.

The analogy mechanism has also been overhauled.  First of all,
reflecting the recent changes, it became increasingly inaccurate to call
it "analogy" and we are now refering to it simply as "production
compilation".  Consequently, the analogy trace (:at) has become
production compilation trace (:pct) and the whynot-analogy and
set-analogized-parameters commands have become whynot-dependency and
set-compilation-parameters respectively.  Also, the dependency slot
stack, which combined the functionality of the dependency slots
subgoals, success and failure, has officially replaced them and those
three slots have been removed from the dependency definition to try to
keep down the number of slots.  Finally, the variable names generated by
the production compilation mechanism now reflect functionality rather
than the original value in an effort to make automatically generated
productions more similar to hand-written productions.

These conventions were adopted for consistency with the "Atomic
Components of Thought" book to be released next year.  The manual will
be updated soon, and in the meantime you should refer to the Notes in
Patches:Release b4 (which also contains the individual patches which
created this version) for details.

Let me (cl at cmu.edu) know if you have any problem, question or suggestion,

Christian