How do you know when your dog has dementia?

Is that even a thing, doggie dementia?

I'm a little concerned about Boomer, our old girl. Lately she's taken to barking a lot. She barks at stuff that doesn't appear to be there, so far as I can see.

Then again, she could be going a little blind.

Her barking will of course get the others to barking, whereupon we find ourselves in the middle of a cacophonous barkfest.

Most unpleasant.