I will answer the first part of the question. It`s not only our eyes but every other sense as well that recipe much, much more sensations than our brain can process. If this would not be the true, we would be overwhelmed with sensory informations, most of which are irrelevant for our actions. However, this vast range of informations provide us with possibility to effectively screen our surrounding, and to pick up those that have a certain quality that potentialy distinguishes them in a sence of their relevance. Just to make an example, New informations will be most likely percived by our brain, as well as anything that moves in our visual field.