It's just one of the thousands McNutt and his curatorial team of Rich Clarkson, Adam Harris and Kate Brainerd considered from the National Geographic archives when putting together a landmark exhibition that's currently on display at select museums around the country (see below).
Switching involves looking at an element of the screen and giving a big blink to select -- the display seems adjusted in such a way that normal blinks won't trigger it, so you're less likely to accidentally set something off.