Today in class (advanced perception), we talked about the human retinal system and the various nerve cells that the signal passes through. It appears that there are many nervous arrangements that pick up 'corners.' The reason why this is important is that these corners are very discriminative; humans can recognize many things from line drawings.
You could imagine a Martian who wants to study the human brain. An analysis of the human retinal system would reveal that we are geared for life on earth (certain arrangements in the retinal system respond to certain visual structures), and the Martian could obtain invaluable details about the world on Earth by studying the human's brain. Of course, the Martian would not know what a particular human saw, he would see what humans as a species (a point in some infinite dimensional space that evolution is traversing) are tuned in to see. He would probably have some knowledge of the distribution of spatial objects that we -- humans -- normally see and have some idea of the density of objects in the human-scale visual world on Earth.
On another note, I googled the term "human retinal system matched filter" and found a paper that was written by Michal Sofka and Charles Stewart about extracting vasculature using a set of matched filters; and even though I meant to find a web page which talked about how certain structures in the eye are tuned in to respond to certina visual stimuli, I found a paper on a different topic which nevertheless mentions my name in the acknowledgements section! (They were using some of the generalized vesel tracing implementation I wrote while researching at RPI.)