I just read the most interesting article in this month's issue of Scientific American concerning "blindsight," a phenomenon by which people suffering from a specific form of visual impairment can still "see" even though they are technically blind. And even though they themselves are not consciously aware that they are "seeing."
I know, that was my reaction also. But it's true! The phenomenon has been known and studied since the early 20th century, but only recently are scientists starting to take the claims seriously and have even come a long way in explaining the source of this singular condition.
People who display this ability have had some form of damage to the visual cortex in their brain. Meaning that their eyes are perfectly healthy, but that the region of the brain that processes what the eyes are seeing is either malfunctioning or not working at all. Yet, with varying degrees of accuracy, most cortically blind people are able to still navigate around objects placed in front of them, make out simple shapes, and even recognize facial expressions in others.
But, here's the kicker -- they don't realize they're doing this!
SciAm has a video up on their website which demonstrates a patient performing blindsight. Click on this link to get to the article, and then wait for the embedded video to load up. It's intriguing to say the least!
Reading the full article (which you can only get by subscribing), I started forming my own opinions on how this was possible. I thought it was telling that only people with damage to the VC would display this ability, while people blinded through direct physical or congenital damage to the actual eyes could not.
Turns out my rationale was leading me to right solution after all. By the end of the article, the author proposes that the visual signals being received by the still healthy eyes, but not being processed by the VC, is instead being processed by an older, less-evolved region in the midbrain called the superior colliculus (SC). In mammals, the SC is responsible for less refined functions of vision such as the movement of the eyes and basic object recognition for use in higher brain functions like the "fight or flight" instinct we all share. In other words, the portion of the visual signal that would normally go to the SC is still going there despite damage to the VC that would normally handle the finer processing of the information our eyes transmit to the brain. So while the VC might no longer be operating as normal, the SC is still doing its job.
And because the SC is used in the processing of mostly unconscious decisions, this also explains why exhibitors of blindsight can perform such uncanny feats and not even realize they are doing it. It's raising a lot of questions--both scientifically as well as philosophically--about just how much of what we see is active cognition. How much of what we used to think we actively processed visually is in fact being handled by a part of the brain connected more with instinct and unconscious brain function?
Food for thought.
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