Babies as young as five months old can understand each others' emotional signals, a new study has found.
US researchers tested a baby's ability to match emotional infant vocalisations with a paired infant facial expression.
"We found that 5 month old infants can match their peer's positive and negative vocalisations with the appropriate facial expression," said Ross Flom, professor of psychology in Brigham Young University.
"This is the first study to show a matching ability with an infant this young. They are exposed to affect in a peer's voice and face which is likely more familiar to them because it's how they themselves convey or communicate positive and negative emotions," Flom said.
In the study, infants were seated in front of two monitors. One of the monitors displayed video of a happy, smiling baby while the other monitor displayed video of a second sad, frowning baby.
When audio was played of a third happy baby, the infant participating in the study looked longer to the video of the baby with positive facial expressions.
The infant also was able to match negative vocalisations with video of the sad frowning baby. The audio recordings were from a third baby and not in sync with the lip movements of the babies in either video.
"These findings add to our understanding of early infant development by reiterating the fact that babies are highly sensitive to and comprehend some level of emotion," said Flom.
"Babies learn more in their first two and a half years of life than they do the rest of their lifespan, making it critical to examine how and what young infants learn and how this helps them learn other things," Flom said.
"Newborns can't verbalise to their mom or dad that they are hungry or tired, so the first way they communicate is through affect or emotion," said Flom.
"Thus it is not surprising that in early development, infants learn to discriminate changes in affect," Flom added.
Flom co-authored the study of 40 infants from Utah and Florida with Professor Lorraine Bahrick from Florida International University.
The study was published in the journal Infancy.