A recent study published in the journal Applied Animal Behavior [0] Science reveals that dog barking is—no surprise to many dog owners—a nuanced form of communication much like birdsong and infant crying. What's more, these forms of communication share acoustic properties in how they convey basic emotions, such as fear—which facilitates cross-species communication.
From the abstract:
"These findings show that dog barks function as predicted by the structural–motivational rules developed for acoustic signals in other species, suggesting that dog barks may present a functional system for communication at least in the dog–human relationship."
You can read the abstract online, and/or purchase the journal article, at the Science Direct website [1]. The Discovery Channel has also posted an article on the new research, which you can read here [2].