Greg Bryant, Associate Professor of Communication Studies at UCLA, talked with NPR about the differences between real and fake laughter. If you're curious to know if someone actually thinks you're funny, you can listen carefully to their breath when they laugh.
During a study conducted by Bryant, they looked for acoustic differences between the two, and here's what they determined:
"Well, I think there are a number of acoustic features that people unconsciously pay attention to, things like higher pitch and loudness, but there also seems to be something that has to do with the breathing. In a real laugh, the proportion of breathiness to valve sound is higher. So there's more breathiness in a real laugh than there is in a fake laugh. And we believe that that has to do with the fact that laughs are produced by different vocal systems so genuine laughs are produced by an emotional vocal system that we share with other animals and fake laughs are produced by the speech system which is human specific."
So, the next time you tell a joke that you know is killer, listen for the breathiness that comes from a real laugh. The whole interview is worth a listen, check it out at the link below.