BOSTON -- Lassie may have barked to "talk" to her owners in the television series that originated in the 1950s, but a recent study shows that dogs don't bark with specific messages in mind.

Kathryn Lord, a University of Massachusetts, Amherst doctoral candidate, worked to define the bark, finding that birds, monkeys and deer make the noise as well. The scientists told reporters from Boston TV station WCVB that dogs do not bark differently in different circumstances, as many biologists believe. She said dogs only bark to ward off predators and deal with conflict.

"What we're saying is that the domestic dog does not have an intentional message in mind, such as, 'I want to play' or 'the house is on fire,'" Lord said.

The barking behavior evolved about 10,000 years ago, when dogs needed to stand their ground to eat at human dumpsites, Lord said. Instead of running away every time a human came near, they participated in mobbing behavior, bravely barking to intimidate intruders instead of running away and wasting food energy.

Some people are upset about Lord's findings, she said.

"I think the main complaints I've seen ... people were upset because they thought their dogs barked in other situations," she said.

However, not all dog noises are barks, she said.

Lord cited another theory called Morton's Rules, a universal mammal noise decoder that categorizes mammal noises as high- or low-pitched, tonal or noisy. For instance, low sounds signal to other animals to go away, but high sounds tell other animals to come closer.

"If you come up to a baby, you don't approach it with a low sound," she said.

Since humans and dogs both follow these rules, they can convey certain feelings, but nothing that reaches complex communication, Lord said.

"There's no deep cognitive understanding, and I think that upsets a lot of people," she said.

Lord said it can sometimes be a "disservice" to the dogs to assume that they have too much cognitive understanding -- her colleagues agreed.

"The reason people can understand their dog's language is they have taught that language," said Terri Bright, of the MSPCA. "When a dog has exhibited a certain type of language, they have achieved a certain consequence. Behavior is shaped by the environment, which includes the owner."