From what you share, it sounds like your mother is experiencing delusions and hallucinations, which are two very common symptoms of Alzheimer's disease.  Due to the damage to the brain caused by the disease, the brain has a difficult time making sense of the environment.  The brain is no longer correctly able to interpret sensory input.  The person with Alzheimer's disease thus hears and/or sees things that are not there, or believes things that are not true.  First, these psychiatric symptoms should be reported to your mother's physician for assessment.  It is also recommended that you try to manage these symptoms rather than try to alter them.  Keep in mind that not all delusions and hallucinations are negative or unpleasant-try to make note of your mother's emotional state when she is exhibiting these symptoms and address the delusions and hallucinations only if they seem to cause her anxiety or fear.  To manage these symptoms, try validation and redirection rather than confirming or denying her beliefs.  For example, you might say, "Mom, I know you miss Dad.  You two were such a happy couple!  Why don't we go for a walk and you can tell me about that big 50^th anniversary party you had?"  You may have to use these techniques over and over, but you will be engaging with your mother in a positive way.