Radio is a great thing. Astronauts who fly high above the earth in orbiting satellites can be heard perfectly though radios here on earth. Communicating by voice alone has its drawbacks, though.
For example, I can't use hand gestures to clarify what I mean. And, as it turns out, that makes a big difference. Researchers at the University of Otago in New Zealand wanted to know how much a relevant hand gesture helps to communicate an idea. They had volunteers watch video clips of a woman saying different phrases, such as "the square box," or "peel the banana."
In some, she simply said the phrase without moving her hands. Peel the banana. In others, she made the kind of hand gesture most of us would make when saying that--a sort of banana-peeling mime that matches the content of the phrase. In a third group, she made gestures with her hands that were unrelated to what she was saying.
The results? People who got the matching content hand gestures remembered those phrases more effectively than folks who got just the words alone. And folks who got just the words alone did better than folks who got irrelevant hand gestures!
What does this show us? We already knew that all the hand-waving we do when we speak isn't just nervous energy; it serves various functions. Apparently, one of them is to help the listener remember what you've said.