Reading a novel when you have dementia

I've been thinking about what it's like to read a novel when you have moderate to severe dementia. My stepdad can no longer follow the plot in a film or drama or Antiques Road Show, constantly asking my mother who is who and what is what and when is Thursday, but he still loves to read. Whenever I visit, he always has a book on the go, on the table downstairs and at night by his bedside. I love to see him reading, absorbed in what he is doing, getting pleasure. I watch and wonder how much he is remembering, I'm fascinated by what he retains from page to page. If you ask him what  the book is about he can't really tell you but he might turn it over and read out the blurb on the back.