Leon Urbas Ljudmilla Nekrasova Sandro Leuchter State chart visualization of the control flow within an ACT-R/PM user model. 43-48 2005 conf/tamodia/2005 TAMODIA http://doi.acm.org/10.1145/1122935.1122944 db/conf/tamodia/tamodia2005.html#UrbasNL05