What you see is not what is out there in the world – not exactly, at least.  Scientists have shown that your brain is tweaking the light coming in from your eyes and making predictions about what you expect to see.
The “blind spot” experiment is well known to students.  That’s where it can be shown that your brain “fills in” the blind spot of each eyeball (where the optic nerve leaves the retina, with no photoreceptors) with imagery from the surrounding field.  A brick wall pattern, for instance, continues seamlessly into the blind spot even though your eye actually receives no light from that part of the retina.
Researchers at the University of Glasgow performed four experiments on participants, and monitored brain activity with functional MRI, to see what parts of the visual field were doing when shielded from visual input.  Their findings were published in PNAS.1  It appears that the context influences what we “see.”  The primary visual cortex (V1) uses context and memory to prepare the image presented to the mind.

We used functional magnetic resonance imaging (fMRI) and pattern-classification methods to show that the cortical representation of anonstimulated quarter-field carries information that can discriminate the surrounding visual context.  We show further that the activity patterns in these regions are significantly related to those observed with feed-forward stimulation and that these effects are driven primarily by V1….

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