Despite dogs' excellent hearing and ability to analyze and process different speech sounds, a new study led by researchers at Eötvös Loránd University in Budapest indicates that dogs fail to distinguish subtle variances between similar-sounding words.
The number of words dogs can learn to recognize remains very low even when they live with humans and are exposed to human speech. Researchers suggest that although dogs have human-like hearing abilities, they might be less capable of coping with nuances between words.
In the study published on December 9 in the journal Royal Society Open Science, the researchers tested this idea. They developed a procedure for measuring electrical activity in the brain of untrained family dogs. The researchers invited dogs and their owners to the lab. After the dog became familiar with the room and the experimenters, the experimenters asked the owner to sit down on a mattress together with her dog to relax. Then, they put electrodes on the dog's head and fixed it with a tape. The dogs then listened to tape-recorded instruction words they knew (e.g., "sit"), to similar but nonsense words (e.g., "sut"), and to very different nonsense words (e.g., "bep").
The analysis of the recorded electric brain activity showed that dog brains clearly and quickly discriminated the known words from the very different nonsense words starting from 200 ms after the beginning of the words. This effect is in line with similar studies on humans showing that the human brain responds differently to meaningful and nonsense words already within a few hundred milliseconds.
But the dogs' brains made no differentiation between known words and those nonsense words that differed in a single speech sound only. This pattern is more similar to the results of experiments with human infants. Infants become efficient in processing phonetic details of words, which is an important prerequisite for developing a large vocabulary.
"But it seems that dogs do not overcome this phase, as they might not attend to all speech sounds forming words. This might also be a factor in why dogs tend to learn only a limited amount of human words, and could mean that they don't understand humans as much as humans might think. Similar-sounding words could be tripping them up, being perceived in their brains as the same thing," said Attila Andics, the study's principal investigator in a report published on the university website.
