Modality Principle: People learn more deeply from pictures and spoken words than from pictures and printed words.

Example: An animation-with-narration version consists of a narrated animation on how lightning storms develop, whereas an animation-with-on-screen-text version consists of the same animation with the words from the narration printed on the bottom of the screen as a caption.

Theoretical Rationale: In the animation-with-on-screen-text version, both the pictures and the words enter the cognitive system through the eyes, causing an overload in the visual system. In the animation-with-narration version, the words are off-loaded onto the verbal channel, thereby allowing the learner to more fully process the pictures in the visual channel.

Empirical Rationale: In seventeen out of seventeen tests, people performed better on problem-solving transfer tests when an animation or set of graphics was accompanied by narration rather than on-screen text. The median effect size was d = 1.02.

Boundary Conditions: The modality principle may be particularly applicable when the material is complex, the presentation is fast-paced, and the learners are familiar with the words. By contrast, printed words may be appropriate when the lesson includes technical words and symbols and when the learner is a non-native speaker or is hearing-impaired.