Dementia has been slowly stealing Ruth Perez's memory and thinking ability for 20 years. Her daughter, Angela Bobo, remembers when it was clear that her mother was never going to be the same.

"She would put food together that didn't belong together — hamburger and fish in a pot. Mom never cooked like that," she says.

The mother and daughter live together in Yeadon, Pa., just outside Philadelphia.

Perez is literally in the center of the family. She spends much of her day tucked under a fleece blanket on a recliner in the middle of the living room. The 87-year-old doesn't seem to notice as her daughter and grown grandchildren come and go, but they keep up a steady one-sided conversation with her anyway.