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Babies can sense one another's emotions by the time they are 5 months old, according to new research from Brigham Young University.

"Babies are very sensitive to emotion, probably from birth," said psychology professor Ross Flom. "In the first five or six months of life, that is the primary means of communication."

Flom has also studied infants' ability to understand the moods of dogs, monkeys and classical music. For this study, he seated infants in front of two screens, one displaying a recording of a happy, smiling baby and the other showing a sad, frowning baby.

He and co-author Lorraine Bahrick, of Florida International University, then tested 40 babies in Utah and Florida by playing audio of a third happy baby.

Of the 20 babies in the study, all 5 months old, 18 turned toward the video of the baby with the positive facial expressions, indicating they matched the happy sounds with the happy baby.

Among the other 20 babies, who were 3½ months old, about half made the connection.

The study was published in the journal Infancy. Five months is also about the time that children usually recognize emotions in familiar adults, Flom said. Feelings of unfamiliar adults are recognizable at about 7 months.

"As parents, we need to be sensitive to children's exposure to affectation or emotion," he said. "They are picking up and attending to the ... exchange."

Twitter: @lwhitehurst