Whether they get smarter or not, I think talking to them is good for their mental stimulation. They do start to recognize words they hear all the time, especially the ones associated with good outcomes (things like 'treat' and 'walk' for the dogs, for instance).
And I think (but I'm no animal psychologist
) that it helps them to bond to their human caretakers if we talk to them. Again, I'm no expert, but it does seem that once bonded, they do pick up on what you're saying more. Some of it might be that they're reading our body language, as well. But once they get to the point that they realize those funny noises you make actually
mean something, it seems like they start picking up on your intent and meaning a lot quicker, doesn't it? I'm not sure how it plays in their head, but on
some level they understand...
(How's that for a word salad, noncommittal reply?
)