What happpens in the dogs' brains when they hear new words?
When science sets out to explore the connection that humans have with their dogs, the results are bound to be fascinating.
For instance, a study Medical News Today reported on last year found that dogs prefer to ignore danger and look at their owners' smiling faces instead. Oxytocin, the "love hormone" that boosts attachment between humans and between humans and their pets mediates this effect.
On a similar note, another study found that talking to your dog in the same way as you would to your baby increases attachment and bonding.
But what happens inside your dog's brain when you "baby talk" to him? Can dogs tell the meaning of different words apart, and could they tell the difference if you said, "Who's a good banana cake?" instead of, "Who's a good boy?"
In an effort to elucidate some of these mysteries, scientists led by neuroscientist Gregory S. Berns, from the Department of Psychology at Emory University in Atlanta, GA, set out to investigate word processing in the canine brain.
Ashley Prichard, a doctoral candidate in Emory's Department of Psychology, is the first author of the paper, which was published in the journal Frontiers in Neuroscience.
Studying dogs inside a brain scanner
Prichard explains the motivation for the study, saying "Many dog owners think that their dogs know what some words mean, but there really isn't much scientific evidence to support that."
"We wanted to get data from the dogs themselves — not just owner reports," the first author adds.
Senior author Berns continues, "We know that dogs have the capacity to process at least some aspects of human language since they can learn to follow verbal commands."
"Previous research, however, suggests dogs may rely on many other cues to follow a verbal command, such as gaze, gestures, and even emotional expressions from their owners," says the researcher.
This new study was part of the Dog Project — a neuroscientific endeavor founded by Berns in which researchers trained dogs, for the first time, to enter and sit still inside a functional magnetic resonance imaging (fMRI) scanner, without being restrained or sedated.
For the experiment, researchers taught 12 dogs of different breeds two different words and trained them to distinguish between the corresponding toys that the words denoted.
At the end of the training period, which lasted for months, the dogs demonstrated that they could discern between the two objects by choosing and fetching the right one when prompted by the owner.
Then, inside the fMRI scanner, the dogs heard both the words they had been trained to recognize and new pseudowords. For instance, the owner would say the words "piggy" or "monkey" several times and then hold up the corresponding toys.
Then, the owner would use control pseudo-words like "bobbu" and "bodmick" and hold up new, random objects, such as a hat or a doll.
How dogs process new words
When comparing the neural response to the known words and the reaction to new words, the results showed a greater bilateral activation in the brain's parietotemporal cortex in response to pseudo-words.
Prichard and colleagues believe that the parietotemporal cortex may be the canine equivalent to the angular gyrus in humans, a brain area that processes lexical differences.
However, the researchers also identified "a subset" of dogs for which the new pseudo-words activated other brain areas, such as the left temporal cortex and amygdala, the left caudate nucleus, and the thalamus.
The scientists explain the significance of the findings. Prichard says, "We expected to see that dogs neurally discriminate between words that they know and words that they don't."
"What's surprising, is that the result is opposite to that of research on humans — people typically show greater neural activation for known words than novel words."
First author, Ashley Prichard
The researchers point out that dogs of different breeds may have different cognitive skills, and that this could be a limitation of the study. Also, mapping the neural circuitry in dogs, in general, is challenging because of varying brain sizes and potentially different levels of intelligence, add the authors.
"Dogs may have varying capacity and motivation for learning and understanding human words," Berns says, "but they appear to have a neural representation for the meaning of words they have been taught, beyond just a low-level Pavlovian response."
Should you use words to train a dog?
However, the researchers point out that the findings do not necessarily imply that spoken words are the best way of communicating with a dog.
In fact, another study carried out by Prichard and Berns earlier this year suggests that the canine brain circuitry responsible for processing reward and facilitating learning is connected to and depends more on visual and olfactory information than it does on verbal cues.
Therefore, "verbal commands may be the least efficient way to train dogs," concluded the previous study.
"When people want to teach their dog a trick, they often use a verbal command because that's what we humans prefer," Prichard says.
"From the dog's perspective, however, a visual command might be more effective, helping the dog learn the trick faster."