How difficult is Vision?

Lately I have been wondering about the problem of Vision and how difficult it should be compared to problem of Artificial General Intelligence.
It seems to me that, given the order that it happened in Nature, processing visual input should be much simpler than using language or reasoning. I say this because there are quite simple animals with eyes, say a fish, a frog or a mouse... As I am not a biologist or neurologist, I am not sure what kind of visual tasks these animals are able to perform. For example, can a mouse tell if there is a cat in a picture or not?
In any case, I guess that these neuronal systems, much simpler than the human brain, are able to solve tasks that we have not yet achieved with Computer Vision algorithms.

If that's the case, I have two questions to my readers, who hopefully can help me clarify these issues:

- What is the "perfect" biological system to understand vision? It should be powerful enough to solve problems that we are interested in, such as distinguishing between different objects, but it should also have a relatively simple brain. Any ideas?

- If animals without human-level intelligence use vision quite effectively, does this mean that Artificial Intelligence will follow the same order of achievements? Or given the properties of computers, it will turn out to be easier to do reasoning, planning or even language processing?

Looking forward to reading your comments.