Dogs that can identify hundreds - even thousands - of toys by name are really rare. That's why they make the news and why books are written about them. Most dogs aren't nearly as good at distinguishing so many different words or learning what they mean.

A new study examined what happens in dogs' brains when they hear words, and the results explain the communication problems most of us encounter from time to time with our dogs. The question posed by the researchers was: To what extent can dogs differentiate words they already know from similar-sounding nonsense words and phonetically very different nonsense words?

Using specific measures of brain activity called event-related potentials, dogs' responses to words can be measured and recorded non-invasively. Dogs are awake during the study and do not need specific training to participate. Electrodes placed on the dog's head allow researchers to record relevant brain activity in response to hearing sounds - either real words or meaningless words.

The experiment improved the dogs' performance on these tests. The more experience they had with a word, the better they were able to recognize it. This is consistent with what Dr. John Pilley says: "Learning builds on learning." He has taught university students and his border collie, Chaser, to identify over 1,000 different toys. Familiarity with toy names allows dogs with large vocabularies to choose the right one, which takes a lot of practice and experience.

Dogs' brains are able to make clear distinctions between a word they already know and a nonsense word that is very different from the known word. However, the study showed that they did not distinguish between the word they knew and a similar sounding nonsense word. For example, their brains reacted differently to words like down and surf, but not to words like down and dune, which differ by only one sound. For anyone who has ever seen their dog confuse signals such as "up" and "stay", or toys such as "boat" and "goat", these results make a lot of sense.

For humans, single-sound differences are an important part of everyday language and communication. In fact, human children learn to make these phonetic distinctions in their second year of life, at which time their vocabulary begins to grow dramatically. Until about one year of age, infants are unable to make such distinctions between similar-sounding words. This study therefore suggests that most dogs process human language in a manner more similar to that of young babies than to that of older babies and young children.

The way words are processed in the brains of dogs with large vocabularies may explain their special abilities. It may be that these dogs are particularly good at processing sounds, and it is this talent that allows them to learn so many different words. Perhaps if the dogs have the ability to distinguish a large number of words and sounds, their vocabulary can grow quickly.

Or maybe the dogs' achievements are related to experience. Perhaps they developed a base of known words and then, with practice, were able to expand it. We don't yet know whether these dogs can distinguish between so many words - some of which are very similar - because of a combination of superior processing and experience, or for some other reason.

Either way, it is fun to communicate with our dogs, and the more we are able to do so, the more we can appreciate each other.