Cognitive Load Theory aims to predict learning outcomes as a function of the way our brains process information and store it both for short and long term use. For a detailed treatment of CLT, you might turn to Cognitive Load Theory (eds. Plass, Moreno, & Brünken, 2010).
For a briefer treatment, Julie Dirksen offers an overview of the architecture of human memory and its implications for course design in Chapter Four of her book, Design for How People Learn. Here’s an excerpt from the chapter:
Consistency can be a useful tool to make things easier for your learner. For example, if you use the same basic format for each chapter of a technical manual, your learners get used to the format and don’t have to expend mental energy repeatedly orienting themselves to the format; instead, they can focus on the content of the chapters.
Too much consistency is bad
However, too much consistency can lead to habituation in your learners. You want to vary your teaching methods and the way you present information. For example, if you are creating an e-learning program and you give the same type of feedback in the same location every single time, then learners are going to ignores it, particularly if the feedback is generic…
Annoying variability is bad, too
While some variation is useful for keeping the learner’s attention, meaningless differences are just irritating….Variation can be a useful tool for maintaining attention, but it should be used in a deliberative and meaningful way.