Learning A New Language

One afflicted with Alzheimer's will start losing their communication skills. It's inevitable. Being a caregiver you need to adapt your speaking techniques throughout the different stages of the disease.
You must learn to speak directly to them as if they're reading your lips. I'll be the first to admit I'm guilty of saying something as I'm walking into another room.
Then returning to speak directly to my father making sure he understood me.
Be patient with them and yourself. This matter gets very frustrating and tiring. Learn to stay away from subjects that might upset them. I won't make a list of subjects to avoid. You'll know which ones they are, and if you don't, you'll quickly figure them out.
You shouldn't ask if they remember this or that. They might not be able to pull a certain thought up at that particular moment, thus causing a snowball of confusion.
When they say things you know are wrong, learn not to correct them. This only puts them in a state of disarray.
Keep your statements short and simple, but please don't demean them by speaking like a child.
If you're giving them instructions, only direct them to do one thing at a time.
If you say to them, "You need to wash and brush you teeth, so we can go to the doctor." That might be too much for them to absorb. Mention one step at a time. You might even get out of the house sooner.
Eventually, you'll start noticing they won't stay on the same subject very long. Stopping in the middle of a sentence, then forgetting what they were saying.
Pay close attention to their "body language." You'll start to learn their facial expressions: Pain, depression, confusion and love.
They're all in there. Be patient and loving, it's as frustrating for them as it is for you.