Caldwell believes he has become a better player since moving south in January, 2010, not least because he is asked to do more defending with Wigan.
"I think the Premier League tests you every week," he said.
"The players are physical and the standard is very high so you have to raise your game and adapt to that.
"At Celtic you were more of a centre half that had to create and start play and didn't defend as much.
"Throughout your career you have different experiences and challenges and that's what brings you on as a footballer."