At what rate do human beings see images?

I remember reading once that something can appear before a person's eye so quickly that their brain doesn't even acknowledge it's existence, even on the subconscious level. This led me to believe that, in a metaphorical sense, we see things in stills that cycle like a movie projector. In other words, do the eyes and optic nerve have a sort of "frame rate", and if they do, what exactly is it?