New York (Independent ): Sometimes it may seem like your dog doesn’t want to listen. But in our study, however, we’ve found that they may understand more than they let on. Human speech is complex, communicating not only words but also tone, as well as information about the speaker such as their gender and identity. To what extent can a dog pick up on these different cues? It’s well established that in humans the left hemisphere of the brain processes meaningful verbal content, as encoded in the fast-changing stream of audible sound.
The brain’s right hemisphere, meanwhile, is more strongly associated with other information the voice carries, such as emotional tone – encoded in the voice’s slow-changing or static layers of sound. Research has shown that if one side of the human brain is better at dealing with certain content in a sound, that content is heard better from the opposite ear. This is because the strongest sound pathways are those that cross-link the sensory organs – such as the ears – to their opposite hemisphere. In other words, the right ear links to the left side of the brain and vice versa. Most people therefore show a right-ear advantage when listening to verbal information in speech and a left-ear advantage when listening to emotional content. Animals also show this left-right distinction in response to sounds produced by their own species. But until now, it wasn’t known whether animals – and particularly domesticated animals such as dogs – respond in a similar way to the various different communicative components of human speech. So we set up a study, now published in Current Biology, to see whether this was the case. Our set-up was pretty simple. Each dog was positioned between two loudspeakers, and either a human voice or another non-voice sound acting as a control was played simultaneously from both sides. We looked at whether the dogs turned their heads to the left or to the right in response to the sound, which indicated which ear they heard the sound more clearly through. For the human voice clips, we modified them to make them either more verbal by emphasising the fast-moving part of the sound, or prosodic, emphasising the tonal, slower-moving part of the sound. We also varied whether the verbal content was familiar to the dogs, such as a command they’d learned, or meaningless to them, such as words in an unfamiliar foreign language.