Do they just choose to ignore us?

A paper by Kaminski et al. in the June 11 issue of Science (also the Sydney Morning Herald) is reporting on evidence that dogs, like children, are able to infer the meanings of new words after a single exposure in a process known as "fast mapping". This knowledge can be retained for at least a month after the first introduction of the new word. Paul Bloom cautions the further testing may be required.

References

Bloom, P. 2004 Science, 304, 1605
Kaminski, J., Call, J. and Fischer, J. 2004 Science, 304, 1682