They can match the sounds of an angry snarl and a friendly yap to photos of dogs displaying threatening and welcoming body language, the research claims.
The new findings come on the heels of a study from the same Brigham Young University lab showing that infants can detect mood swings in Beethoven's music.
Long before they master speech, babies recognize and respond to the tone of what's going on around them.
"Emotion is one of the first things babies pick up on in their social world," said BYU psychology professor Ross Flom, lead author of the study.
Flom and two BYU students report their findings in the journal Developmental Psychology.
"We chose dogs because they are highly communicative creatures both in their posture and the nature of their bark," Flom said.
To reach the conclusion, the babies first saw two different pictures of the same dog, one in an aggressive posture and the other in a friendly stance. Then the researchers played - in random order - sound clips of a friendly and an aggressive dog bark.
"They only had one trial because we didn't want them to learn it on the fly and figure it out," Flom said.
While the recordings played, the 6-month-old babies spent most of their time staring at the appropriate picture. Older babies usually made the connection instantly with their very first glance.