Three-month-old anna grace is staring intently at the new person who just came to visit her parents. what has happened?

I would say that Anna Grace h as learned to respond differently to a familiar stimulus.

So before, when any new person would enter their home, the baby would either not pay much attention to them, or just play or go to sleep. However, now, even though the situation is similar (the stimulus is familiar), the baby has changed the way it behaves around a new person because it started staring at them.