If you're talking about single neurons, then clearly there's a sort of "frame rate," i.e. the absolute refractory period post-action potential. However, unless every neuron in your visual system is synchronized, that single-neuron ARP is meaningless in terms of your entire visual field. (This frame rate would also be exceptionally high...on the order of 300 frames per second, since the ARP of a typical neuron is around 3ms.
The short answer is: we don't see at "frame rates."
The truth of the matter is much more complicated, and it can only be framed in terms of what sorts of stimuli we can effectively resolve. This varies quite a bit by image type. For instance, we can resolve images with very sharp edges at very high effective "frame rates" (i.e. we are no longer able to resolve the images as distinct at a measurable presentation frame rate); images with indistinct or blurry edges, less so. The exact details haven't exactly been hashed out yet, though.
