The Modality Principle

According to Clark and Mayer (2011, p 199-122) when many words are being presented with relatively complex visual displays it is better that the words be spoken rather than written so as to leverage both visual and audio human processing, especially if the visual is an animation or video. 

The following dynamic explanation of a computer simulation of knowledge throughput in a work team that I created has an audio explanation that can be heard while the running simulation can be viewed by learners. This is an example of an application of the Modality Principle.The learners' visual attention is directed toward the running simulation while they listen to an audio explanation of what they are seeing.

Reference

Clark, R. C. & Mayer, R.E. (2011). E-learning and the science of instruction: Proven Guidelines for consumers and designers of multimedia learning. San Francisco: Pfeiffer.