Psychology researchers observed that parents feel emotion while singing to their infants  The researchers hypothesized that this emotion noticeably affects the sound of the singing  To test this hypothesis the parents were recorded while singing to their infants and while singing with no infant present  They were instructed to make the two renditions as similar as possible  These recordings were then played for psychologists who had not observed the recordings being made  For 80 percent of the recordings, these psychologists were able to correctly identify, by listening alone, which recordings were of parents singing to their children
The researchers concluded that their hypothesis was correct
A separate study by the same researchers found that parents feel more emotion when singing to their own children than when singing to other children.