One of the most fascinating of visual experiments was performed on a fifty-two year old African man referred to as ‘TN’ in the scientific literature. He was a tall strong-looking man, a doctor in fact, who in 2004 suffered a massive stroke that knocked out the entire part of his brain responsible for sight called the visual cortex. The visual cortex lies at the back of the brain and in this patient it was completely destroyed. Tests were done on the stroke victim and it was found that he had no residual vision whatsoever. He couldn’t see light or dark, nor could he discern shapes, nor see movement or colour. The visual centre at the back of his brain was quite simply no longer working. He was completely blind.
But his optical system was still working. i.e. his eyes could still gather visual information through the retina – his eyes were still capable of collecting light data and sending it to the visual cortex, but his visual cortex lacked the ability to process the information coming from the outside world.
A group of doctors thought he’d be an interesting subject for study so they recruited him when he was still at the hospital.
There are many types of experiments you can perform on a blind man such as whether he has developed enhanced hearing, or whether he still dreams or has memories from past visual experiences, but one of the experiments that would probably not make your list is whether a blind man can sense your mood by staring at your face. Yet that is exactly what the researchers chose to study!
They began by placing a laptop a few feet in front of him and showing him a series of black shapes on a white background. These shapes were either squares or circles and they told him that the shape was either a square or a circle, and that he should guess what it was. Just take a stab at it they pleaded. TN obliged and he guessed right 50% of the time. Just as you’d expect if he truly had no idea what he was seeing.
Now comes the interesting part. The scientists displayed a new series of images – this time, a series of angry or happy faces. The game was essentially the same, to guess whether the face was angry or happy. Now, you’d expect that it wouldn’t matter what he was looking at, a face, a geometric shape – it was all the same for a man who couldn’t see. But on this test he was able to correctly guess whether the face was a happy face or a sad face 80% of the time!
This experiment has been repeated and the results are the same. When subjects who are blind because of a non-functioning visual cortex are asked to guess whether the face they are seeing is happy or sad – they guess right 80% of the time! Yet, if you repeat the experiment with shapes – they are right only 50% of the time. When it comes to shapes they are guessing, but when faces – they guess right more often then they should.
What is going on here?
When the subject TN was asked how he was able to guess the expression of a face without being able to see – he had no idea. It was something beyond his conscious control. Beyond his conscious awareness. He would simply take a stab at it and he’d be right 80% of the time!
The phenomenon exhibited by TN is called ‘blindsight’. Initially when the results of the experiment were published they were met with howls of derision from the academic community, but they have since become accepted as orthodox and are considered a real phenomenon. But most importantly they shed light on the two tier system of the brain. Beneath the bonnet of what you think is “you” there is a vast city of the subconscious.
Now back to the experiment – how is it possible for TN to perform such a feat?
From the point of view of evolution, it makes perfect sense. You see it was important for our ancestors to gain information about the world they lived in. There is the important visual information such as light, dark and colour – but there is another form of information that would have been important for their survival…the ability to read faces. Especially the ability to discern whether faces are smiling, or look angry. The difference could mean life and death. You’re more likely to approach a smiling face and less likely to approach an angry face – for good reason! Hence faces are important in human behaviour. That’s why in Homers Iliad, Helen of Troy was said to have “the face that launched a thousand ships“, not “the breasts that launched a thousand ships” and its also the reason why we look at the face to get a picture of what someone is thinking and their internal state of mind – and not their elbow!
Faces are so important that there is a special region of the brain especially dedicated to analysing them. It is called the ‘fusiform face area‘ and it is separate from the visual cortex. People who have damage to the fusiform face area, but not the visual cortex, can see faces but they can’t tell you, if asked – whether the face is happy or sad or the expression it has.
So, in the subject TN’s brain the fusiform face area is still receiving signals from the eye. And though he couldn’t see a thing it was influencing the conscious choices he was making when asked whether the face was smiling or not – but TN didn’t know any of this. Only his subconscious brain knew if the face was happy or sad, “he” didn’t! – and it was his subconscious that was allowing him to guess right 80% of the time.
This raises fundamental questions about who “you” are. Where do “you” stop? How much control do “you” have over what you do and how you behave?
In the next post we’ll ponder another question: If I hold my finger in front of my face and then at some point when “I” feel like it, I make it wriggle – and it wriggles, then did it wriggle because “I” told it to wriggle? Most people would say yes it wriggled because “I” made it wriggle.
But as we’ll see, it’s not that simple…and the questions raised threaten to over-turn our very conception of ourselves and what it means to be human.