When people laugh, it is often their cheery sounds or the wrinkles around their eyes that mark out their mirth. Yoji Kimura believes, however, that the key to determining the nature of laughter lies in the diaphragm.

Kimura, 60, professor of sociology at Kansai University in Suita, Osaka, has dug deep into the mechanism of laughter, making it his academic specialty. Having overcome numerous derisive chuckles and cynical sniffs from colleagues and observers, he recently came up with a device that helps him "quantify" laughter.

The device, much like an electrocardiogram for imaging the heart, records muscle movements of the diaphragm by registering subtle electronic signals released from the skin when people laugh.