Spoken language conveys meaning in two ways: the meaning of the words (semantics or lexical knowledge) and the intonation that the speaker uses. We can sense questions by the rising pitch at the end of the sentence. Likewise, we can tell if someone is upset or being sarcastic based on how they say the words. The patterns of intonation in language is known as prosody. There are areas of the brain that are specialized for decoding the semantic meaning of language and different areas for interpreting prosody. In fact, you can have damage to one area during a stroke, while the other area remains intact. There are great examples of this in “The President’s Speech” in Oliver Sacks' book The Man who Mistook his Wife for a Hat.
In most people, word meanings are processed by the left side of the brain and prosody is localized to the right side of the brain. Some animals also use the left side of their brains to understand meaningful and familiar sounds of their species (like alert calls or bird songs). What about for animals, like dogs, which can understand the sounds of another species (i.e. commands from humans). Is the dog brain really processing the intonations of praise “good dog!” or are they responding to the words? Do they process meaning and intonation separately like humans do?
Dogs in MRI machines
In the latest issue of Science, Andies et al. published their studies of language processing in dog brains. My first thought when I read the abstract was “how do you get a dog into an MRI machine?” We commonly study which areas of human brains are active during different tasks using a technique called functional MRI (or fMRI). fMRI was done on these dogs while they listened to their trainers speak. If you have ever had an MRI scan, you know they strap you in and you cannot move your head at all. Same thing with these dogs. Needless to say, they were very well trained dogs. If you still can’t believe it, check out this video the researchers made and the cute photo of dogs in an MRI machine below.
|Really well trained dogs lying still before their MRIs. (Image from phys.org)|
Dogs process language like humans
Okay, so they got the dogs in the MRI machine and scanned their brains while they heard their trainer say different things. The trainer would either say words of praise, like “good boy” (in Hungarian), or neutral words. And they used either a neutral, flat intonation or they raised the pitch of their voice to create a praising intonation. This created four possibilities:
- Praise words with praising intonation
- Praise words with neutral intonation
- Neutral words with praising intonation
- Neutral words with neutral intonation
They compared the brain responses to each combination and found that the left side of the brain responded to words of praise regardless of the intonation. This is amazing, right? The dogs have heard “good boy” enough times that their brains responded specifically to that phrase regardless of how it was said. It’s like they sort of know what it means. It would be interesting to see if they respond to the same phrase spoken by a stranger.
The researchers also found that the right side of the brain had active areas when praising intonation was used, regardless of the word meaning. So dogs also understand how our voices change when we praise them.
Finally, the researchers looked at areas of the brain associated with reward. These areas are active in a variety of animals when they receive natural rewards like food or during sex, but the reward pathways are also active if the animal is given an addictive drug like cocaine. Alternatively, you can put an electrode into a mouse brain that stimulates the reward pathway and the mouse will push a lever to receive an electrical shock in this area of the brain over and over until it starves.
Andies et al. found that praising words spoken in a praising intonation activated the reward pathway in the dogs. Praise words alone and praise intonation alone had no effect. So dogs really do feel good when you say “good dog” in a high pitched voice.
Notice the organization of language processing in the dog brain. Just like in humans, language semantics (praise vs neutral words) was processed on the left side and prosody (praise vs neutral intonation) was processed on the right side. What does this tell us about the evolution of language? Language lateralization has likely been around a long time and is not uniquely human. The authors end the article with this gem: “What makes lexical items uniquely human is thus not the neural capacity to process them, but the invention of using them.”