24. January 2013 · Comments Off · Categories: PhD

The name is an oxymoron, but it’s an actual phenomenon. Humans and other animals that have had their visual cortex removed or damaged in some way (for example by stroke or trauma) can subconsciously “see” in the part of their visual field that is without sight. This almost unbelievable ability is called blind sight.

In experiments where a subject is blind due to removal of their visual cortex (the part of the brain that sees the world around us), but is forced to make a choice or declaration about a target in their blind visual field, the subject will make a correct guess more often than pure chance would allow. For example, the technically blind subject can correctly discriminate between an ‘O’ or an ‘X’ presented in his/her blind visual field to a statistically significant degree.

None of this making sense to you? Me, neither. I thought that visual information is processed in the visual cortex at the back of the brain, and if I was to lose that part of my brain, I would no longer see. It turns out there are exceptions.

Optometry courses and some scientific research going on at Boston University have updated me on my own visual processes. In the middle of your brain there is a structure called the superior colliculus. This area has been highlighted in explaining the cause of this neurological phenomenon. The superior colliculus acts like a subconscious mini visual cortex.

Most of your retinal neurons travel from your eye to the back of your brain to process normal, conscious visual perception. Some retinal neurons, however, dart out of the visual pathway early and enter the superior colliculus. These cells seem to be supplying you with sight that you cannot communicate consciously, but can allow you to orient with your environment subconsciously.

One of my professors gave us an example of superior colliculi function that I think can give you a hint of insight into sensing that your superior colliculus’ subconscious sensory map is there. The example is a visual reflex analogous to when you jerk your hand away from a hot stove before you even realize it hurts your skin. You can similarly begin to orient your head in a position to observe a large moving object approaching you before you ever visually “see” that object. This is the quiet function of the superior colliculus that detects the threatening object approaching you before you have any conscious information about it. The advantage in both reflexes is speed – you gain the ability to react sooner in order to minimize harm to yourself (i.e. get out of the way).

I think that research and new discoveries of this stature keep reminding us to be humble. We do not know everything, some of what we know will eventually be disproved, and there is always room for more discoveries. That is why research is so valuable—the quest will never be complete, but will always take a logical and objective approach to sift fact from false. The humility of science is its inevitably ever-changing ideas. It never declares something “proven,” only presents discoveries with overwhelming evidence and support.