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.
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.
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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.
"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.