I've been on both sides of a lot of interviews, and my suggestion, before you go in, is have a friend or two give you a mock interview. If you can get someone in management to do it, more the better.
Some people are just better at responding to multisensory input. If you typically use your eyes, ears, and hands to evaluate a situation and then decide, it can take a moment to take that situation, and translate it into purely verbal output. A really good supervisor will understand that. Still, you can make it easier on yourself by having a few answers already "translated".