At several points in The Science of Speaking, I talk about power of asking your audience to imagine something. Often, when speakers use this strategy, they will ask their audience to close their eyes.
The results of a 2008 study by Perfect, et al., confirm that this common approach is a good one: when witnesses in the study were asked to close their eyes, they remembered significantly more details—both visual and auditory—compared to witnesses who had their eyes open. This is particularly relevant if you’re asking the audience to imagine something that has already happened (“Imagine a time in the past when you …”), but it likely applies to imagining the future as well (“Imagine a future in which …”).
Another potential application of this technique is in visualization. As I note in the book, the more vividly you can visualize yourself giving a successful speech, the less nervous you will feel about it. This study suggests that to do this most effectively, you should close your eyes when you visualize.