Unified Theories of Cognition: Encoding Productions
From Unified Theories of Cognition, pp. 196-197:
   The total system consists of more than P to C to
   M.  There is a set of productions called encoding
   productions (E-productions) and another set called decoding
   productions (D-productions).  These productions are identical
   in form and structure to the productions of central cognition
   (which can be called C-productions where needed).  They
   differ in being entirely free of the goal context stack.  For them
   there is no such thing as the decision cycle, running to
   quiescence, or impasses -- they fire at will.  In
   contradistinction, cognitive productions are tied to the goal
   context stack by the connectivity constraint.  Each condition must
   either match a goal-context element or match an element that links
   (perhaps through an explicit chain) to a goal-context element. 
   Encoding and decoding productions are distinguished from each other
   only by the functions they perform. 
More about encoding.