Can you tell if someone is smiling even if you aren't looking at them, but just hearing their voice?

Researchers at the University of Portsmouth, in England, have worked on this.  They recorded interviews with volunteers who were asked silly questions, the idea being to make them smile as they spoke.  Then the researchers played the recordings for another set of volunteers and asked them to identify when the speakers were smiling.  And more often than not, they could.

So how is this possible? It's probably mostly that smiling can affect the pitch of your voice, making it sound higher.  So the listeners might have been picking up on that cue.  They also might've been concentrating on the intensity of the voices.  It's not an exact science, obviously, but something was tipping off the listeners.

Eventually, the results of studies like these might help improve voice recognition software as well as synthetic voices for things like computer games.