Overlays: A Theory of Modelling for Computer Aided Instruction
Overlay modelling is a technique for describing a student's problem solving skills in terms of modular program designed to be an expert for the given domain. The model is an overlay on the expert program in that it consists of a set of hypotheses regarding the student's familiarity with the skills employed by the expert. The modelling is performed by a set of P rules that are triggered by different sources of evidence, and whose effect is to modify these hypotheses. A P critic monitors these rules to detect discontinuities and inconsistencies in their predictions. A first implementation of overlay modelling exists as a component of WUSOR-II, a CAI program based on artificial intelligence techniques. WUSOR-II coaches a student in the logical and probability skills required to play the computer game WUMPUS. Preliminary evidence indicates that overlay modelling significantly improves the appropriateness of the tutoring program's explanations.