Summary: Virtual reality (VR) user interfaces are currently more difficult for users to manipulate than a traditional GUI, partly because of more degrees of freedom and partly because VR is still new, so people have less experience using it. Advice for how to employ usability studies to alleviate this problem.
Jakob Nielsen, Ph.D., is a retired principal and co-founder (with Dr. Donald A. Norman) of the Nielsen Norman Group. Jakob established the "discount usability engineering" movement for fast and cheap improvements of user interfaces and invented the heuristic evaluation method.