Coherence principle


… or adding extra material can hurt learning.

People learn better when extraneous words, pictures and sounds are excluded rather than included.

There is a need to remove any media that is not central to the instructional goal of the lesson – a process that Mayer and Moreno called weeding

“Perhaps our single most important recommendation is to keep the lesson uncluttered. In short, […] you should avoid adding any material that does not support the instructional goal.”

Clark & Mayer, 2016. p151.

Some instructional designers have attempted to make use of background music and exciting or interesting imagery, or what Mayer calls seductive details in order to reduce dropout rates on e-learning courses, arguing that their inclusion may motivate learners, but this flies in the face of the body of research.

“When learners use their limited processing capacity on extraneous material, less capacity is available for making sense of the essential content.”

Clark and Mayer, 2016. p152.

Ways to apply the coherence principle

Remove extraneous words

Cute stories and interesting pieces of trivia can feel to the instructional designer like harmless additions to a multimedia presentation, but research suggests that they may not produce the desired effects. The rationale for excluding extraneous words is based upon the cognitive theory that assumes that working memory capacity is very limited.

Clark & Mayer (2016, p155) identify three distinct types of extraneous wording used for different purposes:

  • for interest: related to the topic but not relevant to the instructional goal
  • for elaboration: expands upon the key ideas of the lesson
  • to technical details that go beyond the key ideas of the lesson

They recommend against all three, suggesting that when these additions are more interesting than the fundamental content of a lesson that they can distract learners away from achieving the instructional goals. Not only do they not help learning, but in some cases they can even hurt learning. Evidence for this can be found in many studies conducted over the last 20 years. Mayer, Heiser and Lonn (2001) conducted an experiment that concluded that presenting more information can result in less learning: the addition of additional narration segments to the lesson distracted students away from the core instructional goals. A related study conducted in 2007 found that college students who read the lesson with seductive details “spent less time reading the relevant text, recalled less of the relevant text and showed shallower processing on an essay task as compared to students who read the lightning passage without seductive details” (Clark & Mayer, 2016. p156). Adding seductive details harms learning by distracting learners from the important information and by disrupting the coherence of the lesson.

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