Most dogs respond in specific ways to certain voices and sounds whether it’s another dog, humans using certain tones of voice or other sounds in their environment.
If you’re a dog owner, you can probably also confirm that a chip bag opening or their food bowl being touched will bring them running from the deepest sleeps. Science has finally confirmed this for us in a new study out of ELTE Eötvös Loránd University, in Budapest, Hungary
Studies have shown that much like humans, dogs in wakeful states respond with differing behaviors depending on the valence (levels of positivity and negativity) of vocalizations they hear. They can correlate vocalizations of both dogs and humans with respective facial expressions, and with appropriate pictures. Moreover, in dogs and in humans, sleep has been shown to be important for emotional processing and memory consolidation.
In this study, the researchers wanted to know whether dogs in various sleep stages would show different responses to stimuli of differing valences from different species—in this case, humans and other dogs.
They hypothesized that the research subjects would show sensitivity to both, and recruited owners and dogs (sample size = 13) from the database of the Family Dog Project at Eötvös Loránd University’s Department of Ethology.
Measuring brain responses
The research team measured the dogs’ neural responses only with surface electrodes, a painless and non-invasive EEG method. To place the electrodes, they gained the dogs’ cooperation via positive reinforcement (praise and treats). Each dog was tested individually, and just before the testing began, the dog settled down for its daily nap with its owner sitting at its side.
From another room, while the dog was in states of wakefulness, drowsiness, and non-REM sleep, a research team member played recordings of non-verbal vocalizations from humans and dogs, each of which had been previously rated as having positive or neutral valence. To avoid startling or waking the dogs, no sounds of extremely negative valence were included. Each sound file lasted one second, and each was played at the same volume.
Positive vocalizations from dogs included growls, grunts, moans, pants, and whines; while neutral vocalizations included barks, grunts, moans, and yelps. From humans, positive vocalizations included general and laughing sounds; neutral included coughs, general sounds, moans, sighs, and yawns. No human verbal vocalizations were included, nor were any sounds with sexual undertones, such as sexual moans.
The intensity of the dogs’ responses was recorded in milliseconds, and each testing session lasted approximately three hours. The dogs produced neural responses to each stimulus while they were awake, while they were drowsy, and during non-REM sleep, with varying intensities and slightly longer response times at each successive stage.
Our dogs can hear that chip bag opening
the findings show clearly that ERPs can occur in dogs during states of drowsiness and non-REM sleep, and that the dogs’ brains are able to process them according to species and valence factors, similar to the way humans can process certain sounds as they sleep.
“This finding is significant,” the research states, “insofar as it is the first evidence of complex auditory processing during sleep in dogs.”
Indeed, these results expand our knowledge of dogs’ neural processing abilities and provide a basis for further studies in this area.