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I think an interesting and useful way to think about vision is as a hypothesis. We see a hypothesis of how the world should be. This is why when we walk into our rooms we do not have to look for our alarm clock and we are not surprised when we see a small black cube in our peripheral vision. Our brain has formed a hypothesis of how our room is to look. If there were a tiger in the middle of our room we would indeed be surprised, we did not expect to see that. I think this is a useful way to think about vision because it accounts for the perceived ease of seeing. If we walk into an office expecting it to be a certain way we need not give thought to everything that occurs in our visual field. This makes sense evolutionarily as well. It is crutial for survival that we not be overloaded by giving attention to everything we sense at all times. I am not saying that all we see is this hypothesis. We of course analyze the visual stimuli we receive, and especially the aspects that do not fit into our hypothesis (the tiger).

So there must be an interaction between various mechanisms here. One mechanism forms a hypothesis of the world, based on what we know and expect. One mechanism perceives and analyzes the actual stimuli on the retina. And a third checks how they match up, and pays special attention to where they do not.

An interesting disorder that may result from these mechanisms not functioning correctly is visual agnosia. Oliver Sacks wrote about a man who lost his sight at 2 years of age but was able to have it restored when he was around 50. He had lived his whole life as a blind man. When his vision was restored he had visual agnosia, he could not make sense of what he saw, he was able to see shapes and colors, but not identify them as objects. When he first woke up after surgery he said he could here voices, and see pink circles but was not able to make a connection between the shapes and them being faces.

Maybe this resulted from a problem with his hypothesis forming, and stimuli checking. Since he had lived his life as a blind man his hypothesis of the world was rooted in his remaining senses. His hypothesis of what to expect when walking into his bedroom might have involved the smell of it, how his footsteps would sound, and where he could expect objects to be. So when he was able to see again it proved difficult for him to integrate the shapes he saw with his hypothesis of sounds and smells. He was not able to form a visual hypothesis of the world, and was therefore confused, equally, by all stimuli.

I wonder how far our hypothesis about the world extend. I would be surprised to walk into the dining room and have them serve me a plate full of dirt, I would also be surprised if i ate a grilled cheese and it tasted like steak. How much of what we perceive is first hypothesized about? How much of perception do we miss out on because it doesnt meaningfully contradict our hypothesis?