In most tests of general intelligence, dogs rate as reasonably clever, but nothing like primates. The one place where dogs beat primates is in interacting with humans. It's not clear whether dogs are better at reading human intentions or simply more motivated to act on them, but dogs truly seem to get us.

Now, researchers in Hungary have tested dogs' willingness to cooperate with us by getting them to sit still in an MRI machine. By tracking the dogs' brain activity, the researchers were able to determine that dogs can recognize not only words, but the emotional tone behind them. Dogs recognize when both words and tone indicate praise. That's when they feel rewarded.

The work was performed by a group of researchers based in Budapest, which becomes important when we get to the words the dogs were responding to. The hypothesis behind their work: dogs can recognize both the meaning of what's being said (technically, its lexical content) as well as the intonation used in saying it. In other words, it's not enough to say "good boy" to your dog—you have to sound like you mean it.

To test this hypothesis, the authors got dogs to sit still in an MRI tube. The MRI performed functional scans, which identify those regions in the brain that see an increase in activity after a stimulus. The stimuli in this case were spoken words. For controls, the authors recorded a bunch of conjunctions such as "akár" (meaning "as if" without, presumably, the sarcastic implications). These words were recorded in both a neutral tone and a higher register akin to what is usually used to indicate praise.

Separately, a group of positive statements such as "'ɒzɒz" ("that's it") and "'yɟɛʃ" ("clever") were recorded in both neutral and praising tones. Non-speakers of Hungarian asked to rate the recordings agreed that the praising tone came across, even if the meaning of the words was obscure.

In humans, the left side of the brain specializes in identifying meaning in spoken words. This seems to also be true for dogs. Areas in the left side of the human brain respond specifically to words or phrases that are used to convey praise. In contrast, the Hungarian experiment showed no indication of enhanced activity in canine brains when the conjunctions were played. This suggests, in the authors' words, "that dog brains maintain intonation-independent lexical representations of meaning."

The auditory systems of the dogs tested also picked up on tone, but in this case, it was an area on the right side of the brain that was activated. This showed enhanced activity in response to both praising and neutral words, but there was a difference between the two: responses were stronger to neutral words.

The most compelling result, however, came when the authors looked at the regions of the brain that are used to process rewards. Here, simply hearing words of praise were not enough to cause enhanced activity. Hearing a conjunction in a pleasant tone didn't do so either. The reward centers only lit up when both the tone and the words were consistent with praise. In other words, both the right and left sides of the brain had to agree they were hearing praise in order for the dog to get a sense of reward.

This interpretation may sound like a bit of a stretch, given that the dogs weren't able to actually respond to the praise. But earlier this month, a different team published a paper that also put dogs in an MRI scanner. In that study, the authors also looked at the canine neurological reward centers in order to gauge their dogs' response to either food or praise from their owners. The degree to which their owners drove a stronger response turned out to be predictive of the dogs' behavior when they were placed in a T-shaped room with their owner on one arm and the food in the other.

In other words, if the dogs' brains responded more strongly to their owners' praise, the dog was likely to run towards the owner instead of food. (The owner: food valuation varied among the group of 15 dogs tested, so your mileage with your own dog is impossible to predict.)

Past studies have indicated that dogs can recognize words; it's estimated that they can track up to 1,000 different words associated with items, and they can retrieve the appropriate item on command. But that's a relatively simple form of association. The work here suggests that dogs can actually perceive the meaning of certain bits of human speech.

The authors argue that this tells us something about mammalian cognition more generally and ourselves specifically. Since humans process meaning using both the left and right sides of the brain, our language use may just be an elaboration of a basic mammalian feature. "Lateralized lexical processing does not appear to be a uniquely human capacity that follows from the emergence of language," they conclude, "but rather a more ancient function that can be exploited to link arbitrary sound sequences to meanings. What makes lexical items uniquely human is thus not the neural capacity to process them, but the invention of using them."

Science, 2016. DOI: 10.1126/science.aaf3777 (About DOIs).

Social Cognitive and Affective Neuroscience, 2016. DOI: 10.1093/scan/nsw102 (About DOIs).