Human babies learn words through repetition, obviously, but also by associating words with shapes (in the case of objects). Curious whether dogs learned the names of objects in the same way as people, some researchers at the University of Lincoln in the United Kingdom put a five-year-old Border Collie -- reputedly the world's smartest breed of dog -- through its language-recognition paces. What they discovered was that dogs (or at least this dog) used a different technique than the "shape bias" employed by humans to learn the words associated with objects. From the online scientific research journal Plos One:
Two experiments showed that when briefly familiarized with word-object mappings the dog did not generalize object names to object shape but to object size. [Another] experiment showed that when familiarized with a word-object mapping for a longer period of time the dog tended to generalize the word to objects with the same texture. These results show that the dog tested did not display human-like word comprehension, but word generalization and word reference development of a qualitatively different nature compared to humans.
As to why that is, the researchers speculated that "the evolutionary history of our sensory systems – with vision taking priority over other sensory systems – seems to have primed humans to take into account visual object shape in object naming tasks." Whereas dogs (and many other animals) rely much more strongly on their senses of smell and hearing to make sense of the world. Of course, it's incumbent upon humans as partners and guardians of dogs to also understand how our canine friends communicate with us and each other. Here's one article about understanding dog "talk." Now read this: