In nature, unique vocal rhythms help animals avoid predators or identify potential mates. However, the ability to adapt to foreign speech rhythms, whether for cooperation or competition, has significant advantages. This ability is crucial when it comes to the unique relationship between humans and dogs.
Do Humans Adjust Their Speech to Talk to Dogs?
Do you change your tone when talking to your dog? It turns out that this is not only natural but also beneficial. Eloise Deaux, a researcher in animal behavior and neuroscience at the University of Geneva, analyzed numerous human and dog vocalizations with her team. Their findings show that while dogs generally vocalize more slowly than humans, people unconsciously slow their speech when talking to dogs. "Humans slow down their speech when addressing their pets; it's a modification that brings them closer to the dog's typical speech rate and could facilitate understanding," explained Deaux.
The reason for this adaptation involves both anatomical and neurological factors, specifically neural oscillations-the electrical patterns in the brain resulting from the synchronized activity of neurons.
How Neural Oscillations Help Communication
Neural oscillations, classified by their frequency, have different cognitive roles. Delta waves range from 0.5 to 4 Hertz (Hz), while theta waves range from 4 to 7 Hz. In humans, gamma waves help encode phonemes, theta waves assist with syllable formation, and delta waves play a role in intonation, or prosody.
Anne-Lise Giraud, a professor of neuroscience at the University of Geneva and director of the Hearing Institute, commented on the significance of studying brain waves in dogs: "The study of the role of brain oscillations in the perception of speech is relatively recent, even in humans. So, applying it to our four-legged companions is not insignificant." The researchers adapted non-invasive electroencephalography (EEG) protocols to measure how human and dog brains react to auditory stimuli. "In humans, the theta waves that make up the EEG signal line up with the acoustic envelope, whereas in dogs, it's the delta waves," explained Giraud.
From Behavior to Understanding
Unlike humans, who can verbally express their understanding of a sound, assessing comprehension in dogs requires a different approach. "We used dog-directed speech consisting of commands rather than praises, so that we could objectively measure the intelligibility of the stimuli for the dog, via its execution of the various commands," said Deaux. The team modified the rate of speech and removed content or prosody in order to observe how dogs process language.
Their findings show that dogs are sensitive to both the rhythm and the content of speech. Dogs fail to respond to commands delivered at too fast a rate and can process human language only within a certain range of delta waves, from 1 to 3 Hz. While intonation, or prosody, is important, phonological content also plays a critical role in comprehension. "Our study debunks the myth that dogs are only sensitive to our intonation, or prosody. Phonological content is important if they are to understand what we say," said Deaux.
Broader Implications
The research team hypothesizes that dogs and humans have coadapted to improve communication. However, they question whether this adaptation is exclusive to dogs or can also be observed in other domesticated animals such as cows, sheep, or goats. Studying how humans communicate with other species could offer additional insights into the coadaptation process.
By comparing the communication abilities of domesticated dogs with wild canids like wolves, researchers may be able to distinguish the linguistic abilities developed through genetics versus socialization. The NCCR Evolving Language's Special Interest Group (SIG) Canid Cognition is investigating this area. As Deaux explained, "A better understanding of the dog's cerebral mechanisms will enable us to gain knowledge about humans and our evolution."
Research Report:Dog-human vocal interactions match dogs' sensory-motor tuning
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