A study suggests that dogs interpret speech patterns the same way humans do. Photo by jarmoluk/Pixabay
Oct. 29 (UPI) -- Dogs interpret words from speech using computations and brain regions similar to human infants, a study published Friday by Current Biology found.
Based on measurements of electrical activity and changes in blood flow in the brain, dogs appear to be able to track words and syllables spoken by humans the same way humans do, the researchers said.
Electroencephalograms, which measure electrical activity in the brain, and functional magnetic resonance imaging, or fMRI, scans, which detect changes in blood flow in the brain, performed on dogs suggests that the animals use similar brain regions to interpret speech.
"We know that in humans both general learning-related and language-related brain regions participate in this process -- and we found the same duality in dogs," study co-author Marianna Boros said in a press release.
"Both a generalist and a specialist brain region seemed to be involved in statistical learning from speech, but the activation patterns were different in the two," said Boros, a postdoctoral researcher at Eötvös Loránd University in Hungary.
In dogs, the "generalist" brain region -- the basal ganglia -- responded more to a random speech stream, where no specific words could be detected using syllables, than to a structured speech stream in which words were easy to spot just by computing syllables.
Meanwhile, in dogs, the specialist brain region -- the auditory cortex -- responded more to the structured speech stream.
In humans, the auditory cortex plays a key role in statistical learning from speech, Boros said.
"We believe that this activity increase is the trace word learning leaves on the auditory cortex" in dogs, she said.
A study published in August by Scientific Reports suggested that dogs process speech hierarchically, just like humans, meaning they process intonations first, at lower stages, and word meanings at higher stages.
Similarly, human infants can spot new words in a speech stream before they learn what those words mean, according to the researchers.
To learn new words from continuous speech, infants must not only count how often certain syllables occur together, they need to also calculate how likely it is that these syllables occur together.
To tell where a word ends and another one begins, they make complex calculations to keep track of syllable patterns, in essence learning that syllables that usually appear together are probably words, and those that do not probably are not words.
This is how infants solve the seemingly difficult task of word segmentation -- "they calculate complex statistics about the probability of one syllable following the other," Boros said.
The new findings suggest dogs may also recognize such complex regularities in speech, according to the researchers.
For this study, Boros and her colleagues measured their electrical brain activity using electroencephalogram, or EEG, readings, as well as fMRI scans, which revealed the brain regions responsible for the complex computational capacity in dogs.
The tests were performed on awake, cooperating, unrestrained animals previously trained to lay motionless during the time of the measurements, the researchers said.
The researchers observed differences in dogs' brain waves with frequent versus rare words, as well as brain wave differences for syllables that frequently occur together compared with syllables that only occasionally do.
This indicates dogs keep track not only of simple statistics, or the number of times a word occurs, but also of complex statistics, or the probability that a word's syllables occur together, which has never been seen in other non-human mammals, according to the researchers.
However, how these human-analogue brain mechanisms for word learning emerged in dogs remains unknown, the researchers said.
"Until now we did not know if any other mammal can also use such complex computations to extract words from speech," Boros said.
"Dogs are the earliest domesticated animal species and probably the one we speak most often to, [but] we know very little about the neural processes underlying their word learning capacities," she said.