Cognitive constraints on multimedia learning: When presenting more material results in less understanding.

In 4 experiments, college students viewed an animation and listened to concurrent narration explaining the formation of lightning. When students also received concurrent on-screen text that summarized (Experiment 1) or duplicated (Experiment 2) the narration, they performed worse on tests of retention and transfer than did students who received no on-screen text. This redundancy effect is consistent with a dual-channel theory of multimedia learning in which adding on-screen text can overload the visual information-processing channel, causing learners to split their visual attention between 2 sources. Lower transfer performance also occurred when the authors added interesting but irrelevant details to the narration (Experiment 1) or inserted interesting but conceptually irrelevant video clips within (Experi-ment 3) or before the presentation (Experiment 4). This coherence effect is consistent with a seductive details hypothesis in which the inserted video and narration prime the activation of inappropriate prior knowledge as the organizing schema for the lesson. Multimedia scientific explanations—in CD-ROMs, on the World Wide Web, and in classroom demonstrations—are po-tentially valuable instructional tools. For example, Figure 1 shows selected slides from a 140-s multimedia explanation intended to help students understand how lightning storms develop. The multimedia explanation uses animation to depict the steps in lightning formation along with corresponding narration to describe them. Our research has documented that well designed multimedia explanations formatted like the one in Figure 1 can be highly effective in promoting students understanding, as indicated by their ability to generate accept-able answers to open-ended transfer questions (Mayer, 1997,