Dogs don’t understand human speech as well as we think they do, brain scans reveal

BUDAPEST, Hungary — Many dog owners will be happy to tell you how smart their four-legged friend is. While canines may seem to know exactly what humans are saying from time to time, a new study finds their vocabulary isn’t as robust as their doting owners might think. Researchers in Hungary say brain scans show dogs actually can’t figure out the difference between words they know and ones that sound very similar but mean nothing.

A team from Eötvös Loránd University examined a group of untrained dogs from the local community to see just how much human speak our furry friends understand. Although dogs have excellent hearing abilities, the research finds they don’t see the difference in words which only differ by one speech sound. For example, a dog’s brain tends to react the same way when they hear “dog” and “dig.”

Overall, dogs can understand various human sounds that come from distinct letters like d, o, and g. This is very similar to the neural processing of words by humans. The difference is dogs can only learn a small number of words throughout their lives, according to researchers, even if they live with a human family and hear them speak all the time.

What’s going on in the canine brain?

To test their theory, lead author Lilla Magyari and her team created a procedure to measure electrical activity in the brains of dogs while they are awake. Electroencephalography (EEG) is a common method of examining human brain patterns, but dogs are usually sleeping when scientists attempt the procedure on them.

In this study, researchers invited untrained, family dogs into their facility and allowed them to get comfortable sitting on a mattress with their owners. Once relaxed, researchers attached non-invasive electrodes to each dog’s head using tape. With the electrodes is place, each dog listened to tape recordings of humans saying instruction words like “sit.”

The dogs then heard as the recordings switched to similar but nonsense words like “sut” and then to extremely different words like “bep.”

“The electroencephalography is a sensitive method not only to brain activity but also to muscle-movements. Therefore, we had to make sure that dogs tense their muscles as little as possible during measurement. We also wanted to include any type of family dogs in our study not only specially trained animals. Therefore, we decided that instead of training our dog-participants, we will ask them just to relax. Of course, some of the dogs who came to the experiment could not settle down and did not let us do the measurement. But the dropout rate from the study was similar to the dropout rate in EEG studies with human infants,” Magyari, a postdoctoral researcher at Department of Ethology, explains in a university release.

How big is a dog’s vocabulary?

The results reveal dogs can clearly distinguish between regular words they know and very different-sounding nonsense words. They’re able to tell the difference within 200 milliseconds of someone saying the words to them. This is actually in line with human brain responses to meaningful and nonsense words.

Unfortunately, dog brains show little change when encountering regular words and nonsense words which are only one speech sound off. These results are similar to the reactions of human babies under 14 months-old.

Researchers say infants become more efficient at processing sound details between 14 and 20 months. This allows them to build a large vocabulary as they grow into toddlers. Younger infants don’t have this ability to process detailed information even though they can understand speech sounds weeks after birth.

“Similarly to the case of human infants, we speculate that the similarity of dogs’ brain activity for instruction words they know and for similar nonsense words reflects not perceptual constraints but attentional and processing biases. Dogs might not attend to all details of speech sound when they listen to words. Further research could reveal whether this could be a reason that incapacitates dogs from acquiring a sizable vocabulary,” principal investigator Attila Andics concludes.

The study appears in the journal Royal Society Open Science.

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