Victoria Ratcliffe, University of Sussex
There's no denying people like to natter away to their pooches. But is man’s best friend actually listening? How do they process this information so that they know to run to the window when they hear squirrel that hide in the corner when they hear the dreaded, “Bath time”? Are they paying attention to both, what we say and how we say it? Georgia Mills talked to Victoria Ratcliffe from the University of Sussex, who’s been investigating the canine way of listening...
Victoria - Speech is quite a complex signal and it’s got a lot of information being transferred at the same time. one of the things humans do is we divide the information up and it’s processed in different areas of the brain. So, we wanted to compare whether dogs also divide this information and how similar it is to the way that we do it.
Georgia - As I'm talking to you now, you're not just processing what I'm saying, the words, but also the way I'm saying it, the intonation. What's more, these types of information are dealt with by different sides or hemispheres of your brain. The left hemisphere processes the what and the right processes the how, but how would you find out if this is the case for Fido?
Victoria - We used a behavioural design called head orienting design which has been used with lots of different animal species to look at how this process their own species vocalisations. So, the way it works is you have two speakers that are placed either sides of the dog and have found this played from both speakers at the same time, so that the sound enters both of the dog’s ears equally. When sound input goes in through each ear then it’s transferred mainly across to the opposite hemisphere of the brain. The hemisphere which is more specialised in processing information works more efficiently. So, the sound is heard more clearly from the opposite ear.
Georgia - In other words, you can work out which side of the dog’s brain is processing the information from which way they think the sound is coming from, shown by which way they look. To tease apart words and intonation, some interesting sounds were played to the test subjects. There were phrases the dogs were familiar with…
Exited voice - Come on then!
Georgia - Then there were phrases with neutral intonation, just contain the words the dog knew…
Neutral voice - Come on then…
Georgia - And also some sounds with intonation but without any meaning…
Recording - [exited buzz]
Georgia - And it looks like, like humans, dogs process both the meaning and the intonations of human speech. They process this information in separate hemispheres just like we do.
Victoria - They showed different biases for the different information speech so that the fact that it had biases in the first place is consistent with the idea that they're perceiving the different information in the signal. So, they're not just getting one aspect of the information out. Also, because they showed opposite biases to the verbal information versus the speaker related information, then it suggests that they're processing these two main aspects of speech differently in different areas of the brain. When they heard the verbal content that was meaningful to them, so the familiar command…
Recording - Come on then.
Victoria - They responded differently to when it was not meaningful to them…
Recording - Thom on cen.
Victoria - So, it suggests that the way they're dividing the speech up depends on the relevance to the information to them rather than just the way it’s encoded in the signal.
Georgia - But is this very human way of listening shared only with man’s best friend or can it be found across the animal kingdom?
Victoria - So, we don’t know if dogs show these different biases because during domestication, it’s possible that humans have selected dogs that respond quite well to spoken commands. It would’ve been probably beneficial for them to adapt to be able to understand different information in speech so that they can cooperate and cohabit with humans. So, it could be that dogs have converged in a way that they've evolved with humans or it’s possible that other animals would also show this ability if they had enough exposure to speech. So, it could be that lots of different mammals have the potential to have these differences, but we’ve just seen it in dogs because they're exposed to speech quite a lot in their everyday lives. So, one of the things we’d like to test is whether these differences are also shared in other species of mammal. If they were then it would suggest that these differences that we see in humans in relation to speech have ancient ancestral origins that are shared across different mammals.