What is a ball?
For humans, the answer is rather evident. A ball can be large or small, fuzzy or smooth, and still be a ball. Young children learn this quickly. If a tennis ball is a ball, they soon recognise that a football is also a ball. However, this process works quite differently in dogs.
Even if a dog truly knows what you mean by “get the ball!”, it seems to consider the term ‘ball’ in a very different way. People generalise on the basis of shape: a tennis ball is round, as is a football. They are both balls. Scientists wanting to find out how dogs generalise did experiments on a five year old border collie. The dog was taught a specific name for a number of objects. After a short training period the dog did appear to generalise, but on the basis of size, not shape. The dog assumed that any two objects of the same size had the same name, even when the shape was very different. The training continued. The dog learned to associate words with objects having similar textures; the shape still didn’t matter.
Dogs do understand words. If you say, “get the ball”, the dog knows that you’re talking about the ball. But it thinks about a ball in a different way than we do: the size and texture are significant for the dog, while for us, the shape is more important. The investigators suspect that the difference has to do with differences between human and canine evolutionary development. Because humans have to rely much more on sight, we are more focused on how objects look.