Actually, as far as vision goes, a lot of visual processing happens in the neural networks built into the eyes themselves, before the electro/chemical signals even get to the optic nerves that then lead to the brain. I think of our senses as filters. An electronic information filter always leaves out much and also always leaves its fingerprints indelibly on the information it does pass. This is a large part of why our senses are not objective, but subjective. Understanding visual subjectivity and its effects gives visual artists some special abilities in their artwork.