My rats know their names, but my boy that just passed away this morning would show he heard you, but like a stubborn dog, would only come if he really wanted to. He was usually too busy marking territory, burrowing, playing and sniffing tasting things. He was really independent, but the smartest rat I have.
But my other boy just lOOOOooooves cuddling with me. He pees on my arm just about everytime I bring him to cuddle to remind me "I'm his". :rolleyes: He comes when I call him and loves to get scratches and little ear massages. :) He's my doozer.
Rats are incredibly smart, but it does take time to get them to trust you if they are nervous and really open up and show you just what they can do. I try to take time and always play with my new girls I'm growing up because raising rats, even for feeders, is so much fun when you have a little animal that loves to see and play with you.
For my rats, I consider them not pooping outside of the cage to be litter trained. Since I only have 2 truly "pet only" boys who pee wherever they go, not pooping is a sign that they have been potty trained.
I haven't tried too hard, but none of my girls know litter training in their cages. I'm sure the boys would, but never put too much time into it.