I know this might be unusual since people usually ask the opposite question, but I simply have to ask this.
It's about this question: Can a human size object move so fast that it ceases to be observable?
I really think that this question belongs on https://cogsci.stackexchange.com/ (maybe https://biology.stackexchange.com/ since it also includes the neuroscience tag). Also I think it should have been put on hold in order to improve.
Here are my reasons:
1) It's about perception.
The author of the question wants to know whether "regular audiences" or a "normal person" can see it or not, the author isn't asking whether it's detectable by other physical means. To be fair, there are some physical considerations that we have to worry about here but I can't see how a physicist could conclude the issue, it has to come to the issue of human visual perception and that's not physics. The visual system is far from an idealized camera.
2) The questions is badly posed.
First of all, the title is very misleading, it's clearly not about the moving object, it's about the observer. And I don't see how it helps if the object is superhuman and if we have the exact dimensions of the space in which the superhuman is confined. The motion is practically arbitrary, only limited by special relativity and the object's only limitation is it's approximate size.
I think we can safely say that the question can be translated into:
Is it possible for an everyday-sized easily visible object to evade human visual perception by moving sufficiently fast in a confined space?
When you put it this way, I think it's even more clear that a physicist cannot give a final word here.