July 21, 2009 -- A pair of new studies on human babies reveals that six-month-old infants can detect basic emotions when listening to two distinct sounds: barking dogs and Beethoven's music.
Together, the studies suggest babies recognize and respond to the tone of what's going on around them long before they master speech.
"We think that infants have the capacity to discriminate and recognize emotion in a variety of contexts," lead author Ross Flom told Discovery News.
"Early researchers often focused, and rightly so, on human faces and voices, and now we are seeing evidence that infants discriminate and recognize emotion in a variety of domains -- music and now canine expressions," added Flom, a professor of psychology at Brigham Young University.
For the research that involved dogs, Flom and colleagues Daniel Hyde and Heather Whipple first showed 128 boy and girl infants pictures of the same dog, with one picture depicting the dog in an aggressive posture and another photo showing the dog in a friendly stance.
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Next, the researchers played, in random order, sound clips of a friendly, playful dog barking and an aggressive dog barking.
"They only had one trial, because we didn't want them to learn it on the fly and figure it out," Flom explained.
As the recordings played, the six-month-old babies spent most of their time staring at the appropriate picture. Other studies have proven that this staring is a baby's way of making a connection. The babies therefore correctly matched each dog bark to its corresponding photo.
The findings are published in the journal Developmental Psychology.
For the second study, published in the journal Infant Behavior and Development, Flom and co-authors Douglas Gentile and Anne Pick played five happy-sounding melodies, as well as five sad-sounding melodies, all composed by Ludwig van Beethoven (1712-1773). Prior work by the team determined Beethoven's music contains a variety of distinctive emotions, which is why his pieces were chosen for the study.
This time, the researchers displayed an emotionally neutral face for the listening babies. Whenever the scientists switched from a happy to a sad Beethoven melody, or vice versa, the babies stared at the image more, due to heightened interest. Earlier research shows this extra attention proves infants notice, and then respond to, changes.
BYU music professor Susan Kenney, who did not work on either study, was surprised by the Beethoven research findings, since the music and its underlying structure are complex.
"The happy songs were all in major keys with fairly short phrases or motives that repeated," Kenney said. "The tempo and melodic rhythms were faster than any of the sad selections, and the melodies had a general upward direction."
"Four of the sad songs were in minor keys and all had a slower beat and long melodic rhythms," she added. "For an infant to notice those differences is fascinating."
Babies detecting sounds produced or composed by other humans may be impressive, but it's even more surprising that babies should identify emotions conveyed by another species, namely dogs. Numerous studies suggest mammals can identify basic emotions in each other's vocalizations, but humans seem to be particularly good at detecting different emotions in dog barks.
But would babies then be equally successful at identifying emotions produced by another popular house pet, the domestic cat?
"As a cat owner, I doubt it, though it really is an empirical question of course," Flom said.
He and his team hope to further analyze baby abilities, in hopes of better understanding how infants learn so rapidly, and how human sense of perception develops and changes over time.
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