Abstract
This paper provides an overview of studies of the effects of learner prior knowledge on multimedia learning and describes new approaches to building learner-adapted multimedia environments based on those findings. On many occasions, multimedia formats that are effective for low-knowledge learners appear to be ineffective, or even deleterious, for high-knowledge learners (the expertise reversal effect). A possible explanation of the effect takes into account a working memory overload during the integration of instructional information with available knowledge base in long-term memory. The major implication is the need to tailor dynamically the design of multimedia environments to changing levels of learner expertise using appropriate online methods of cognitive diagnosis.