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A little matter of perception

Picture this. You are walking along a wild and empty beach, the honey-coloured sand cool beneath your feet. The sky is still blue, but the setting sun paints the silver clouds in shades of orange, pink and purple. You feel the grains of sand crunching underfoot, and see the foot prints you’ve left behind. You discern the blue bottles on the sand, notice the sharp edges of shells and the smooth surfaces of pebbles, and step effortlessly around them because you know exactly where your body is in space and time. To your right, waves roll in, tumbling onto the beach with all the power of the ocean behind them. You see the shimmering shades of water rise up, and trip over itself in a flurry of white foam. At the same time you hear the slurp and splash and crash of a wave making its way to shore, and the waft of the ocean deep - the salty, fishy tang of the sea breeze - reaches your nose. You experience this all as one perfectly synchronised percept; a consistent and coherent

conscious experience brought to you by your senses working in harmony together.

It is easy to think that you receive this information in complete form – a carbon copy of reality painted onto your mind with perfect fidelity. And yet, that is not what is happening at all. Each part of this holistic experience is manufactured by different parts of the brain, from a limited range of completely separate and quite different types of real-world stimulus.

Your eyes capture a particular range of wavelengths of light (the visible spectrum). Your ears filter sound waves down to the eardrums, to be converted into mechanical signals that can be picked up by your cochlear. The receptors in your nose captures chemical molecules from the air and those in your feet receive different stimulus again, that of the sensations of pressure and temperature. Each individual system cleverly transduces those signals into electrical impulses that trigger a cascade of electro-chemical responses that allow these various physical inputs to travel from the outside world to the brain, where they are processed to create what you experience while walking down the beach at the onset of twilight.

It is not necessarily an accurate picture of reality, mind you, rather a creation of the brain – a perception – shaped by a very specific range of external stimuli. Stimuli we have evolved to experience, because somewhere along our evolutionary line it enhanced our survival. Other animals can sense things like electrical fields (sharks) or magnetic fields (turtles, butterflies), giving them access to quite different information about the world. Who knows what else we might be missing? Our brains, locked away in the black cave of our skulls, can only work with what it has access to. And what it has access to is determined by the particular receptors we have about our bodies.

And we don’t even pick up on all the information available, even within those specific channels. Sounds we can’t hear, light waves we can’t see. Butterflies, bees and reindeer can see in the ultraviolet spectrum, and some frogs and snakes in the infrared - neither of which the human eye is tuned into. Dogs can smell things we can’t - sniffing out drugs and fruit at airports, and apparently smelling cancer.

Not only are all the inputs vastly different, each of these sensations – sound, touch, smell, sight, taste, proprioception, balance – are all processed in separate areas of the brain. The visual information travels to the occipital cortex at the back of your head, the symphony of sound to your temporal cortex, and your somatosensory information – the senses that come from your skin and muscles and the ligaments between them – travel to your parietal cortex. And yet, we see and hear and feel things in a coherent manner, despite the fact that light travels faster than sound or touch, for example.

In effect, what you experience is not reality but a creation of the brain. A perception that, while certainly objectively real in some sense, is entirely created by the brain bringing together the different stimulus it has access to, and forming a picture based on previous experience. The blue bottle does exist, it is not just in our imagination, but the brain doesn’t see a blue bottle, it sees patterns of light and dark spread across its binocular retinas that differentiates it from its surrounds, and categorises as a blue bottle, based on past learning. Moreover, what we see influences what we hear - for example our vision shapes the words we perceive - and what we hear influences where we perceive objects are in space.

Another example of the brain creating reality from limited inputs is the fact that the brain receives 2-D information but creates 3-D perceptions. The back of the eye, where our photo receptors reside, is a 2-dimensional space. A flat space. Yet we see in three dimensions because of how the brain combines the pattern of activity from each eye, which are slightly separated in space. (Try these illusions to experience some of these brains clever tricks for yourself).

Colour is another example of the brain’s ingenuity. You can only “see” colour with a tiny portion of your eye – the fovea, where light concentrates on the back of the retina and forms the focus of your vision. It is here where the three-cone receptor system that enables colour vision exists. Yet, your peripheral vision right now, despite only receiving monochromatic signals, appears in colour to you. That’s just your brain, your wonderful brain, filling stuff in. Making your reality feel consistent, real and coherent.

So, next time you take a walk along a beach, talk to a friend or visit an art museum, remember to be grateful to your marvellous brain for painting you such a glorious experience.

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