Dale Purves M.D. is a researcher investigating human vision and he believes that vision is a reflex. Moreover he thinks that what we see is actually a synthetic representation of what we think we see based on our own memories and previous experiences. here is a snippet from Duke Univ medical news:

Basically, say Purves and Lotto, their evidence demonstrates that what humans and other mammals see is a reflex response to the accumulation of possible sources that a given stimulus has turned out to be in past experience. This way of generating vision explains why visual perceptions are often at odds with physical measurements of the underlying objects -- the angles and line lengths of a simple geometrical figure, for instance.

For example, he said, it is impossible to know whether a given amount of light reaching the retina signifies a highly reflective surface in weak illumination, or a weakly reflective one in strong illumination. Since the amount of light and therefore the effect on the retina is the same in either case, the viewer's perception cannot be a simple "report" of the amount of light reaching the eye from the surface in question.

"What we see has to correspond to what is really out there -- the shiny surface or the dull one," says Purves. "If that weren't the case, we would all be in deep and continual trouble with respect to the responses we make to retinal stimuli."

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Ironically, Purves explained, this central problem identified more than a century ago has taken a back seat in the twentieth century, primarily because of rapid progress in anatomical and neural recording techniques that have proven enormously successful in determining how the nerve cells in the visual system are wired. Despite the scientific success from using these techniques, said Purves, the successes have not kept the implicit promise that understanding the detailed wiring of relevant parts of the brain will lead to a general theory of vision.

For more check out Purves's Lab's URL: http://www.purveslab.net/seeforyourself/