As parents love to say, “It’s not just what you say, but how you say it.” Now, a new study shows that the same applies to dogs. Our furry friends process speech much as people do. They can differentiate the tone of voice from the meaning of words.
Meaningful words or phrases, like “good boy,” activate the right side of a dog’s brain no matter how they’re said. But the brain processes the tone of voice used to speak a word or phrase on its left side.
The same is true in people, although the side of the brain that is activated is reversed. We process what something means using the left hemisphere of our brains. And we interpret the tone in which it’s spoken using the right side. This process allows us to distinguish words with meaning from random sounds. But researchers didn’t know whether that division of labor in the brain evolved before or after people acquired language, says Attila Andics. He’s a neuroscientist at Eötvös Loránd University in Budapest, Hungary.
Dogs have a close connection to people. That makes them ideal for testing how they process speech. “Humans use words towards dogs in their everyday, normal communication,” Andics points out. "And dogs pay attention to this speech in a way that cats and hamsters don’t."
He and his team trained dogs to lie very still. Then they scanned the animals’ brains using a functional MRI (fMRI) machine. It shows when and where a brain responds as signals come in. During the scan, the scientists played the dogs the recorded voice of a trainer. This person spoke meaningful praise words, such as “good girl,” or neutral words, such as “however.” The tone of voice used could be either neutral or enthusiastic.
The dogs showed increased activity in the left side of their brains when they heard the meaningful words but not the neutral ones. Meanwhile, an area on the right side of their brains reacted to the tone used with the words. It could separate out those spoken enthusiastically from those spoken without emotion.
The combination of both praising words and an enthusiastic tone of voice caused the reward center — a part of the brain associated with getting something pleasing — to become more active. That means that the dogs had the same neurological response to an excited “Good dog!” as they might to being petted or receiving a treat. When praise words or an enthusiastic tone were used separately, they didn’t have the same effect.
Andics and his team described their findings in the Sept. 2 Science.
The role of language
Use of language separates people from other animals. Humans are the only species to manipulate precise sequences of sounds to convey different meanings. But the new study suggests that the ability to hear these random sequences of sound and link them to meaning isn’t exclusively human.
“I love these results,” says Laurie Santos. She’s a cognitive psychologist who works at Yale University in New Haven, Conn. The new findings “point to how well domestication has shaped dogs to use and track the very same cues that we use to make sense of what other people are saying,” she says.
Domestication has made dogs more attentive to human speech. But people and dogs have been close companions for only about 30,000 years. That’s just not long enough for dogs to have evolved complicated language-processing skills that use both sides of the brain, says Andics. So the trait must go back far earlier. He suspects it comes from some older neural technique used to make sense of meaningful sounds. And he believes it is not limited to humans and dogs.
Unfortunately, testing this in other species — even pets — could prove difficult. Why? Cats, he notes, don’t take as kindly to being put inside fMRI scanners and asked to hold still.
Correction: The side of the brain that is affected in dogs has been corrected for an error that the authors had introduced into their original paper. The authors posted a correction in the April 7 issue of Science. The lead author, Attila Andics, says his team's major finding still stands: that dogs process different aspects of human speech on different sides of their brains.
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canine Members of the biological family of canids. These are carnivores and omnivores. The family includes dogs, wolves, foxes, jackals and coyotes.
cognitive A term that relates to mental activities, such as thinking, learning, remembering and solving puzzles.
domestication A process of producing a tame version of an animal or plant from a wild one, which can take many generations. A domesticated animal is one that has been bred in captivity for food or as a pet.
evolution (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.
fMRI (functional magnetic resonance imaging) A special type of body scan used to track brain activity. It uses a strong magnetic field to monitor blood flow in the brain. Tracking the movement of blood can tell researchers which brain regions are active. (See also, MRI or magnetic resonance imaging)
hemisphere Half of a globe, which can refer to half of the Earth, half of some ball, or anything else — such as half of the brain.
mechanism The steps or process by which something happens or “works.” It may be the spring that pops something from one hole into another. It could be the squeezing of the heart muscle that pumps blood throughout the body. It could be the friction (with the road and air) that slows down the speed of a coasting car. Researchers often look for the mechanism behind actions and reactions to understand how something functions.
neural Relating to neurons (nerve cells) or to the nervous system.
neuroscience Science that deals with the structure or function of the brain and other parts of the nervous system. Researchers in this field are known as neuroscientists.
psychology (adj. psychological) The study of the human mind, especially in relation to actions and behavior. To do this, some perform research using animals. Scientists and mental-health professionals who work in this field are known as psychologists.
random Something that occurs haphazardly or without reason, based on no intention or purpose.
reward center (Also reward system) A region of the brain that processes the pleasant reactions we get when we get smiles, gifts, pleasurable stimuli (including food) or compliments.
scanner A machine that runs some sort of light (which includes anything from X-rays to infrared energy) over a person or object to get a succession of images. When a computer brings these images together, they can provide a motion picture of something or can offer a three-dimensional view through the target. Such systems are often used to see inside the human body or solid objects without breaching their surface.