Seeing Is Believing, or v.v.
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 a nonstimulated 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.
The way PhysOrg put it, “What our eyes can’t see, the brain fills in.” And it fills it in from prior experience: “The results show that our brains do not rely solely on what is shown to the eyes in order to ‘see’. Instead the brain constructs a complex prediction” of what it expects to see.”
One neuroscientist called this “predictive coding.” Dr. Lars Muckli from U of Glasgow explained how this is helpful: “If you are driving a car and a pedestrian is suddenly obscured – say by a pillar box or your rear view mirror – your brain still knows where they are and where they will reappear in your line of vision. Without that ability, we would be lost in everyday life.”
For more on image processing done by the eye and brain, see 05/22/2003, 12/30/2003, 05/12/2005, 07/27/2006 and 03/31/2008.
1. Smith and Muckli, “Nonstimulated early visual areas carry information about surrounding context,” Proceedings of the National Academy of Sciences USA, published online before print November 1, 2010, doi: 10.1073/pnas.1000233107 (open access). Note: the paper was published Nov 1, 2010, but PhysOrg reported on it April 4, 2011.
Unfortunately, Dr. Muckli tossed in this Darwin stinkincense bomb: “The brain’s main function is to minimise surprise – that is what it has evolved to do.” Were you surprised? That not only violates logic, it violates Darwin’s own principle of Stuff Happens. Things don’t evolve to do anything in Darwinland; they just evolve. Implying a purpose for anything invokes teleology – something Darwin and his disciples wanted to eliminate. Enough of that distraction.
Findings like these bear on important philosophical questions about the relationship of our senses to external reality. Philosophers have long wondered to what extent we can trust our senses. There is a long chain of causal phenomena interceding between the photons emitted by an object and our perception of that object by the mind. Here we see that our brains are manipulating reality for us in ways that can be tricked by experience or novelty.
Those who say they only believe what they can see should realize they cannot see the whole electromagnetic spectrum, for one thing, and the narrow range of visible light they can see is being transformed by their brains. The only worldview that provides grounds for trusting our senses comes from the Bible. Our eyes and brains were created by a Creator who loves honesty and truth, and has equipped his creatures with sufficient equipment to have reasonable, though not exhaustive, access to external reality. Otherwise we would be “lost in everyday life” and unable to respond to him by perceiving his works. Even so, we need to train our equipment to discern the truth, and not deceive ourselves.