This wiki refers directly to visuals.

Research has shown that learners benefit immensely from visuals during a lesson or presentation. The visual aspect of a presentation is extremely important as it helps to grab and maintain the attention of the audience, reinforces points being made by the presenter thus helps with understanding, and concretize the presenter’s points into the long term memory of the audience. 

Note that the visuals enhance the presentation, which is in no way suggesting that the speaking or presenting aspect is not just as important. What the visual aspect does, once used correctly, is to help set and maintain the tone for the presenter. Remember, visuals could be open to a number of interpretations by the audience; however when the presenter verbalizes, the audience is directed to the points which are being made. 

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