Working memory (previously referred to as short term memory) has a very limited capacity and can only hold a few pieces of information at a time. It is therefore important that we help learners process essential facts and avoid cognitive overload.
Although only limited amounts of information can be stored, this information can be split amongst the visual/pictorial and auditory/verbal channels. As L&D designers we can take advantage of this by ensuring each channel is utilised, rather than relying on one channel at a time. For example, rather than having an image and explanatory text (both of which require processing in the visual/pictorial channel) why not include an audio explanation to an image, therefore using both channels and allowing the learner to process more information.
It is also important to remove any extraneous details from the learning which don’t support the instructional objectives. This includes decorative images, sound effects, music and even facts and stories designed to add interest.
Although a well meaning L&D designer may add these materials to engage the learner, by giving the working memory extra bits to process they will make it more difficult to learn the important parts. The best way to engage a learner is by helping them learn and apply what they need to know to progress.