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.
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| 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.”
