Through the Eyes of the Blind

I went to college to become a science writer, but I had a bigger plan. I’d cover breakthroughs in neuroscience and nuclear physics by day and then I’d write killer science fiction by night.

I made my way through copy editing and ad writing classes while cramming in all the science and creative writing my schedule allowed. I did manage to get a fantastic well-rounded education and I left with more than a diplomma. I had a pretty decent roadmap for my life.

Then, well, life happened instead and it wasn’t even close.

However, I still have a great deal of respect for those scientists who communicate well, and those writers who love and understand science. Together they explain facts and theories about the amazing universe in which we live.

I host book tours on my other blogs and when I get a guest post that impresses me, I like to repost it here. In late March I featured author and neuroscientist Michael Tranter, PhD and his popular science book  A Million Things To Ask A Neuroscientist. I got to ask him a question and I wanted to know what he thought was the most amazing thing in his book.

Enjoy his answer.

How can you be blind but still see?

(The brain is amazing, that’s how!)

At the back of the brain we have the occipital lobe. This region receives images from our eyes and optic nerves and decides what we are seeing before sending that information to other parts of our brain to determine how to react. So, if we see an adorable fluffy dog, the light reflected from that dog travels to our retina at the back of our eye, along the optic nerve and to the occipital lobe, where it is processed. Other areas then interpret the meaning and decide what the emotional response should be, resulting in a very excited ‘Aww, a cute puppy – I like this, I feel happy!’

However, damage to the occipital lobe, for example, through trauma, a brain tumour or a stroke, can result in the images of the cute puppy arriving at the visual areas safely, but not being processed or transmitted to other areas of our brain, and hence, we become blind. This is a little different to instances where the eyes or optic nerve don’t function. This additional blindness is termed cortical blindness – essentially, blindness in the brain. You may be asking why I am talking about cute puppies and blindness. Well, because in some people with cortical blindness, even though they can’t see particular objects, their subconscious brain still perceives them. This means a person can interact with something even if they don’t actually see it. Let’s use another example. Say you want to walk across the room to the doorway, but there is a chair in your path. Under normal circumstances, you would see the chair and walk around it. A person with blindsight would also walk across the room and avoid the chair, yet they would not actively see that there is a chair in the room. They simply avoid it but do not fully understand why.

This strange phenomenon was first documented in the 1974 research by Lawrence Weiskrantz and has since been recorded in all manner of situations. A person may catch a ball in mid-air without ever seeing it, for example, but perhaps the most interesting study shows how it is possible to identify facial emotions and even mirror those same emotions in your own face, without ever being consciously aware of seeing any facial expressions.

Blindsight has been rigorously tested in many experimental settings, and as such, neuroscientists think they have an explanation. Firstly, the fact that some people with cortical blindness experience the phenomenon of blindsight may be because the superior colliculus – an area of the brain important in visual orientation – is preserved. Although we don’t yet fully appreciate the full function of the superior colliculus, we do know that this area receives information about what we see and converts it into signals that initiate an appropriate movement. To help explain this, imagine sitting down and watching a racing car drive past. Our eyes and head would instinctively follow the car as we track its movements. This is the responsibility of the superior colliculus, to instinctively monitor the environment and decide how to move our body.

The current hypothesis for blindsight states that as the brain senses damage to the occipital lobe, it starts to rewire itself to bypass the visual areas. The person may never entirely regain normal vision, but they may still be capable of living a normal life. Some neuroscientists suggest that this is a process by which the brain reverts back to a more basic form of vision, and one that is seen in animals who naturally lack the advanced visual areas of a human brain.

So, there you have it. That is how you can be blind, but your brain can still see, pretty amazing right?

For the full post, which was part of a blog tour sponsored by Goddess Fish, check out A Million Things To Ask A Neuroscientist.

 

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