Interaction, External Representation and Sense Making

Why do people create extra representations to help them make sense of situations, diagrams, illustrations, instructions and problems? The obvious explanation – external representations save internal memory and computation – is only part of the story. I discuss eight ways external representations enhance cognitive power: they provide a structure that can serve as a shareable object of thought; they create persistent referents; they change the cost structure of the inferential landscape; they facilitate re-representation; they are often a more natural representation of structure than mental representations; they facilitate the computation of more explicit encoding of information; they enable the construction of arbitrarily complex structure; and they lower the cost of controlling thought – they help coordinate thought.