Have you ever tried to watch a movie with captioning on, and the audio turned off? This is what trying to follow an e-learning with only text instruction is like. A solution to this challenge is provided by the Modality principle, which states that a learning designer should present words as speech rather than on-screen text.
A handy infographic summarizing Ebbinghaus's 1885 theory on memory retention and the forgetting curve.
By distilling a topic down into its fundamental definitions, characteristics, and concepts, you can manage the essential processing of a learner by covering these up front. That way, learners can instead focus on the causal connections between concepts in the rest of the lesson or course. This is a principle known as Pretraining.
Can you imagine watching sports without the constant on-screen graphic giving you the score? Would you believe this wasn't the norm until 1994? This is what signaling in learning design is all about. Numerous studies have shown that humans learn more deeply when visual and/or verbal cues are added to highlight the organization of the essential information.