Dog lovers have been saying it for years: dogs are smarter than many people give them credit for.

Now, scientists are joining in. Over the past decade, research into canine behavior and intelligence has been blossoming, and a range of experiments have suggested that dogs are capable of surprisingly complex feats of social intelligence and emotional sensitivity. On the whole, psychologist and dog researcher Stanley Coren estimates, the average dog's intelligence is roughly as sophisticated as a 2.5-year-old baby's.

the average dog's intelligence is roughly as sophisticated as a 2.5-year-old baby's

So far, research has suggested that dogs can read our cues, show emotional connection to their owners, and even display jealousy. Studies have found that the brightest dogs appear to be capable of learning hundreds of words. It's likely that these abilities have been shaped by evolution — over thousands of years, we've selected those dogs best adapted to live with humans.

The field is still new, however, and researchers keep finding out a surprising amount. "Most labs have historically been invested in rodent and monkey models," says Gregory Berns, an Emory neuroscientist who conducts MRI research with dogs. "But dogs are unique animals, and I think in many ways they're one of the best animals for understanding social behaviors."

Using newer technologies such as MRI as well as carefully designed behavioral experiments, a handful of labs around the world have dug into the dog psyche — and found that they're much smarter than many people assume.

1) Dogs are adept at reading people — often better than chimps

Chimpanzees and human infants younger than a year or so usually fail a very simple test of implicit communication: a person sets two cups upside down on the ground and points at the one with a treat hidden underneath. It sounds absurdly simple, but both chimps and babies are unable to interpret this as a cue to find the food, and they investigate the correct cup first only about half the time.

Dogs are different. A series of experiments conducted by Brian Hare of Duke University found that dogs do interpret this cue, going for the correct cup at rates far higher than chance. (This was true even when both cups were scented to smell like the treat.) Dogs seemed capable of interpreting human stares and nods toward the right cup.

In other experiments, dogs that are trained not to take a piece of food do so much more often when an observing human has left the room, closed his or her eyes, or turned away. Again, it sounds very easy, but understanding the significance of a gaze in this way is something chimps do not seem to be capable of.

Still other studies show that dogs can pick up on our judgments of objects and act accordingly. In one, for instance, dogs observed their owners open two boxes but couldn't themselves see what was inside. The owner acted positively about the contents of one box (smiling, speaking in positive tones, and leaning toward it) and negatively for the other (recoiling in shock and speaking in angry tones). The dogs went to the former box 81 percent of the time — a finding that's similar to the results of the same experiment conducted with 18-month-old babies.

2) Dogs can learn hundreds of words

Dogs vary in their ability to remember things — just like humans and members of all animal species. But some dogs with particularly good memories, scientists have found, can be trained to remember more than 1,000 different words.

The most famous case is a border collie named Chaser, who has been trained by a retired psychology professor named John Pilley. As documented in a 2011 study in Behavioral Processes, Chaser has learned the names of 1,022 different toys — when directed to pick a specific toy up, she retrieves the correct one about 95 percent of the time. More recently, Pilley has trained Chaser to recognize verbs, as well: she now knows the difference between picking up something, putting her paw on it, and putting her nose on it.

Chaser's abilities might be unusual, but she's not unique. Another border collie named Rico has been shown to recognize more than 200 different words, and is capable of a cognitive process called "fast-mapping" — when he hears a new word, he knows to go get a new toy, rather than one he's already learned the word for.

3) Dogs pay attention to the words of our speech — not just our tone

Many people assume their dogs can only process the tone of their speech — but experiments by Victoria Ratcliffe, a psychology researcher at the University of Sussex, suggest their brains are processing the actual words, as well.

In human brains, the left hemisphere primarily processes language, and the right hemisphere primarily processes emotion and tone. Sound that enters our right ear is directed to the left hemisphere — and vice versa. So for most people, we disproportionately interpret language using sound from our right ear and interpret tone with the left.

Ratcliffe showed that dogs have the same bias. "We had speakers on either side of the dog and played a noise from both at the same time," she says. When they played commands the dogs were familiar with, the dogs disproportionately turned to the right, and when they played distorted speech, or commands in a language the dogs had never heard before, they mostly turned to the left.

"in both the human brain and the dog brain, these 'voice areas' are located in very similar places"

"This told us that they're paying attention to different calls, and processing words they already know in a different way than others," she says. In ongoing work, she's looking at exactly what information dogs associate with words they've learned.

Some fMRI work — which involves training dogs to lie still for up to 30 seconds in scanners, which track blood flow to different areas of the brain as a proxy for brain activity — has confirmed these findings. Experiments at Hungary's Eötvös Loránd University have shown that when dogs hear human voices, there's a specific area of their brain that shows significantly more activation than when they hear nonverbal noises.

"The very exciting finding is that in both the human brain and the dog brain, these 'voice areas' are located in very similar places," lead author Attila Andics told me for a previous Smithsonian article on the findings.

4) Dogs are emotionally connected to their owners

Some of the most fascinating canine MRI work has come from Berns's lab at Emory. In one of his most striking experiments, Berns found that when dogs sniffed a rag soaked in their owner's scent, activity spiked in their caudate nucleus — a reward center involved in emotional attachment. But it didn't spike when a stranger's scent was used instead. He also found that the same spike occurs when a dog's owner walks into the room, but not when strangers do.

In more recent experiments, Berns has put dogs in an fMRI and had various people show them a signal that means they're about to get a treat. "Dogs that scored lower on tests of aggressiveness had a caudate response that was really tuned just to their owner," he says.

More aggressive dogs, on the other hand, showed equal spikes in the reward system when any human gave the signal. His lab is now working with service dog organizations to see if this sort of test could be used to see which dogs are most suitable for service.

5) Dogs can feel jealousy

Traditionally, the emotion of jealousy was thought to occur only in primates. But a few different recent studies have provided evidence that dogs feel it, too.

In one experiment, researchers from the University of Vienna first trained dogs to present their paw (that is, "shake hands") in exchange for a treat. They then conducted the experiment with pairs of dogs, arbitrarily rewarding only one, and found that the other dog stopped participating. This wasn't just frustration at not getting a treat: when the same dogs participated in the experiment alone, and didn't have the chance to see another dog getting rewarded, they participated for a much longer period of time without rewards.

the emotion of jealousy was thought to occur only in primates

In another study, meanwhile, psychology researcher Christine Harris confirmed what many dog owners have long suspected: the animals also get jealous over attention given to other dogs.

In the experiment, she had owners ignore their dogs, giving attention to either a pop-up book or a robotic stuffed dog toy that could bark and wag its tail. When researchers blindly analyzed video of the experiment later, they found the dogs exhibited significantly more jealous behaviors (such as growling, snapping, and rubbing up against the owner) when the object was the stuffed dog, rather than the book. This result was the same in similar experiments conducted to measure responses of six-month-old babies.

Still, there are limits to dogs' intelligence

Many of these abilities likely stem from dogs' evolutionary history. Their ancestors, after all, were the wolves who were quickest to adapt to living around humans, and for tens of thousands of years since, they've been specifically bred for their ability to be trained by us. It's logical that this selective pressure would lead to animals that are especially attuned to human voices and emotions.

But some scientists feel that dogs' acute sensitivity to humans might actually lead us to overplay their intelligence. They're remarkably attuned to our actions, but they certainly don't always grasp the meaning behind them. As canine cognition researcher Clive D. L. Wynne told the New York Times, "It’s a happy accident that doggie thinking and human thinking overlap enough that we can have these relationships with dogs, but we shouldn’t kid ourselves that dogs are viewing the world the way we do."

"we shouldn't kid ourselves that dogs are viewing the world the way we do"

One good example of this — and of many dog owners' tendency to overestimate the animals' understanding of the world — is a series of experiments conducted at Barnard's Horowitz Dog Cognition Lab that studied what's commonly called the "guilty look."

Dog owners often report that they can tell from their dog's impression, upon arriving home, if the dog misbehaved while left alone. But the researchers, led by Julie Hecht, left dogs alone in a room with food that they'd been trained not to eat, then filmed and rigorously analyzed their interactions with their owners (who didn't know whether they'd misbehaved or not) when they returned.

It turned out that for the most part, the misbehaving dogs didn't really act any guiltier then the others: dogs from both groups basically just responded to getting chastised by their owners by showing characteristically "guilty" looks.

Dogs love humans, are good at reading us, and are eager to please us. But that doesn't mean they know right from wrong. Instead, they simply feel sad when they let us down.

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