totally opposite. the attire is very casual. most wear hawaii shirts and khakis. if you are giving a paper presentation, maybe you wear a shirt with a collar. the most important thing is to make sure you are wearing that dorky badge around your neck or security won't let you into the poster session.
You'll see people from shorts and sandals to suits. You never know who you will meet. So I would suggest wearing khakis and short-sleeved collared shirt (or maybe even a buttondown), something not too casual but not too formal. Just as rubensam said, make sure you wear the badge at all times.