Your Eyes Don't Actually See
When we think of sight and seeing, it's normal not to think too much about it. That it's just part of being human and having this body. However it is quite a complicated process. And it starts with light.
Without a light source, we can't 'see' anything. The light waves travelling from a source whether its the sun, a light bulb or a screen, are crucial for us to 'see' our environment.
It is the light waves travelling, elementary particles called photons, moving in every direction, bouncing off objects in a given environment and bouncing back into our eyes. So our eyes are actually detecting light, and the brain creates the experience of seeing.
From Photons To Signals
The light reflected from the world enters the eye and hits the retina, which is at the back of the eye. The retina has cells called rods and cones which each have their own function when it comes to detecting light. Once light has been detected, these cells convert the information into electrical signals.
Those signals travel through the optic nerve to the brain. The brain then receives these signals and applies meaning.
A Huge Amount Of Information
The visual system in the brain processes an enormous amount of information. The brain needs to work out things such as colour, movement, shape, contrast, depth and where objects are in relation to each other. Different areas of the visual system specialise in processing these different bits of information.
Around a third of the cerebral cortex is involved in visual processing, demonstrating just how much of our brain is devoted to processing seeing.
And yet we aren't consciously aware of most of it.
Your Brain Fills In The Gaps
There is simply too much information for the brain to consciously process so the brain has to filter and prioritise. The brain uses information that it has already learnt in the past by recognising familiar shapes, movement and colour. It also predicts what might be there.
Really, the brain is constructing a representation of the world rather than giving us a perfect copy of everything in front of us. This is why sometimes we think we see things that are not actually there. And also why optical illusions work so well.
The eyes are receiving information, but the brain is interpreting that information using its existing assumptions and processing systems.
When Vision Goes Wrong
This system can also be disrupted unfortunately and can be a very difficult experience for people. Damage can happen to the eyes themselves, or to the brain and the visual processing areas.
Someone may be able to see an object but struggle to recognise what it is. Another person may have difficulty recognising faces or processing movement. Damage to the eyes means that individual unfortunately can't receive the wavelengths of light and so the brain has to compensate with the other senses, to ensure the individual can navigate their environment.
A Constructed Reality
Every time you look around a room, you experience what feels like a complete picture of reality. But what you are actually experiencing is your brain's interpretation of incoming information. Light bounces around from objects into your eyes, and the cells in your eyes detect that light. The signals are sent to the brain and the brain processes and filters information out. You then experience a visual world.
While an incredibly useful system, it is a constructed one. We don't experience the world exactly as it is. We experience a version of the world that is unique to ourselves, a version that our nervous system is capable of building using the information it receives plus the information it has already learnt.
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