As Coyle explains, "One of the quickest ways to deepen practice is also one of the simplest: Close your eyes. . . It sweeps away distraction and engages your other senses to provide new feedback. It helps you engrave the blueprint of a task on your brain by making even a familar skill seem strange and fresh."
I realized while reading this that I've asked my choir to close their eyes and sing in the past, but I haven't done it for quite a while. This does several things: as Coyle mentions, it "sweeps away distraction" and makes "even a familiar skill seem strange and fresh." But it also forces the choir to listen much more intensely. They have to listen and use other skills (maintaining an inner sense of pulse) to stay together as an ensemble without watching you conduct (and perhaps you realize you aren't as necessary as you thought! Or better, you can use your gesture more for shape and direction than keeping time).
I do sometimes stop conducting and ask my ensemble to sing without me—I want them to shape phrases independently, to concentrate on subtle details of ensemble, even learning to feel ritards together.