When it comes to learning, external representations, aka visualizations, have always been valuable tools to students. Visualizations play a key role in all learning.
So why are visuals important?
According to The Theory and Practice of Online Education: Students learn better from words and graphics or pictures than from words alone. There is the The Spatial contiguity principle, where students learn better when corresponding words and pictures are presented near rather than far from each other on the page or screen. The Temporal contiguity principle, where students learn better when corresponding words and pictures are presented simultaneously rather than successively. Lastly, The Redundancy principle, where people have only limited capacity to process visual and auditory material presented simultaneously; therefore, students learn better from graphics and narration than from a combination of other materials.
So what visuals should you put in your online class?
Visuals that emphasize the critical details relevant to learning are most effective.
Simple line drawings, tend to be superior to photographs or more realistic drawings depending on the learning task.
Of course graphics, which can increase the motivation of users to attend, prompt perception, and aid recall, and assist in the development of higher order thinking and concept formation.
Graphics: Pictures, Illustrations, Charts, Diagrams, Graphs, and Models.
Diagrams, Charts and graphs should require the learner to process the information given and to understand certain conventions.
Graphics should guide the student
Captions on Photos and Illustrations.
Increase learning by focusing attention on appropriate elements of illustrations.
Overall, many theories support the importance of visualizations as a complement to learning. Incorporating visuals in online courses is both beneficial to the students, as well as the course, and has a profound impact on how students perceive information, learn, and judge usability. More articles regarding visuals in online courses can be found here and here.