Here’s what happens in your dog’s brain when you speak

2022-04-05

My dog Leo clearly knows the difference between my voice and the barks of the beagle next door. When I speak, he looks at me with love; when our canine neighbor makes his mind known, Leo barks back with disdain. A new study backs up what I and my fellow dog owners have long suspected: Dogs’ brains process human and canine vocalizations differently, suggesting they evolved to recognize our voices from their own.

“The fact that dogs use auditory information alone to distinguish between human and dog sound is significant,” says Jeffrey Katz, a cognitive neuroscientist at Auburn University who is not involved with the work.

Previous research has found that dogs can match human voices with expressions. When played an audio clip of a lady laughing, for example, they’ll often look at a photo of a smiling woman.

But how exactly the canine brain processes sounds isn’t clear. MRI has shown certain regions of the dog brain are more active when a pup hears another dog whine or bark. But those images can’t reveal exactly when neurons in the brain are firing, and whether they fire differently in response to different noises.

So in the new study, Anna Bálint, a canine neuroscientist at Eötvös Loránd University, turned to an electroencephalogram, which can measure individual brain waves. She and her colleagues recruited 17 family dogs, including several border collies, golden retrievers, and a German shepherd, that were previously taught to lie still for several minutes at a time. The scientists attached electrodes to each dog’s head to record its brain response—not an easy task, it turns out. Unlike humans’ bony noggins, dog heads have lots of muscles that can obstruct a clear readout, Bálint says.

The researchers then played audio clips of human and dog vocalizations. The human sounds included only nonlanguage vocalizations like baby babble, laughter, and coughing, whereas the dog sounds included sniffing, panting, and barking. Each sound was classified as conveying either a “positive” or “neutral” emotion, based on the context they were made in, like the excited yelp of a dog playing with a ball. (The researchers didn’t include any “negative” sounds so as not to startle the pups.)

For each of the noises, the dogs experienced a change in brain waves within the first 250 to 650 milliseconds. In human brains, signal differences in this time frame are associated with motivation and decision-making. That suggests to Bálint and her co-authors that the pups are trying to figure out who or what is making the sound—and how to respond. The dogs’ brains didn’t produce any meaningful signals in the first 250 milliseconds, the time period in which humans tend to process sound qualities like pitch or tone. That suggests, Bálint says, that the dogs weren’t simply noticing the voices sounded different.

Moreover, when the dogs’ brain waves peaked in the 250- to 650-second range, they fired differently depending on who they were listening to. The waves were more electrically positive in response to human vocalizations, and they were more electrically negative in response to the canine sounds, the researchers report today in Royal Society Open Science.

Bálint stresses that “positive” and “negative” in this case refer to the changing electrical voltage of the brain, and not the intensity of the signal or the preference of the pooch to hear one sound over another. But the difference in voltage between the waves triggered by human sounds and those triggered by dog sounds was stark, she says. The dogs’ brains are processing the two types of sound in different ways, but exactly how is still unknown.

Some of the sounds the researchers used were clearly species-specific, such as a bark or a laugh, says Rochelle Newman, who studies how dogs and humans process language at the University of Maryland, College Park. But other vocalizations in the study might not be so easily parsed. “I don’t know if human and dog yawns are acoustically distinguishable,” she says. If they aren’t, then the dogs might be distinguishing the sounds based on other, additional criteria.

But Katz says the data are robust—and important. Knowing how dogs process sound could, among other things, help canine experts better train service or working dogs. Bálint would like to test how dog brains react to other types of stimuli, but not until she repeats this experiment with more dogs. That’s no walk in the park: “You’d have to train more dogs to lie completely still for at least 7 minutes,” she explains.

Science, 5 April 2022
; https://science.org