Validating that a real user can correctly perceive the motion of a virtual human is first required to enable realistic interactions between real and virtual humans during navigation tasks through virtual reality equipment. In this paper we focus on collision avoidance tasks. Previous works stated that real humans are able to accurately estimate others' motion and to avoid collisions with anticipation. Our main contribution is to propose a perceptual evaluation of a simple virtual reality system. The goal is to assess whether real humans are also able to accurately estimate a virtual human motion before collision avoidance. Results show that, even through a simple system, users are able to correctly evaluate the situation of an interaction on the qualitative point of view. Especially, in comparison with real interactions, users accurately decide whether they should give way to the virtual human or not. However, on the quantitative point of view, it is not easy for users to determine whether they will collide with virtual humans or not. On one hand, deciding to give way or not is a two-choice problem. On the other hand, detecting future collision requires to determine whether some visual variables belong some interval or not. We discuss this problem in terms of bearing angle.