Whether or not a medium's capabilities make a difference in learning depends on how they correspond to the particular learning situation--the tasks and learners involved--and the way the medium's capabilities are used by the instructional design. Tasks vary in their situational characteristics and the demands they place on the learner to create mental representations of certain information and operate on that information in certain ways. Learners vary in their processing capabilities, the information and procedures that they have stored in long-term memory, their motivations and purposes for learning, and their metacognitive knowledge of when and how to use these procedures and information.