Simulator sickness could effect human's performance. I would like to run an experiment to check the association of sickness severity and performance. Any idea of performance test that did not involve human intelligence?
You could ask your participants to perform tasks that can be objectively evaluated (and be compared with / normalised for IQ scores if necessary) - we used a simple target tracking task to evaluate performance in a fligth simulator. http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044381