The Looking Glass Club gruff davies New Scientist

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Perception versus reality

Colour doesn't physically exist

We think that the real world is full of colour, but colour doesn't 'exist' in a physical sense.  It is an interpretation, something our brains construct to simplify the huge amount of information our retinas catch in the form of photons.  Photons, particles of light, behave like waves with frequencies or wavelengths - not a single one of them is green or blue or red.  Our retinas have receptors which catch three narrow ranges of wavelengths of light (these don't even correspond exactly to red, green and blue as many people assume.)  In fact, photon wavelengths vary enormously outside the small range which we can see.  We don't even see the vast majority of the 'real world'.  


Most people find the idea that colour isn't real very hard to accept. So, let me show you.


1. Girl with one blue eye

Professor Akiyoshi Kitaoka of Ritsumeikan University, Japan, created this wonderful illusion. This girl seems to have lost a blue contact from her right eye, but her left eye is clearly blue, isn't it? In fact, it is not. Both eyes are exactly the same shade of grey as the blow up to the right shows.  Some people even insist the left eye is bluer in the larger picture, but look at the solid block of grey joining them.  If you think it's a trick, cover the surrounding red areas with something, or grab the image into photoshop, or print it out and cut the eyes out to see for yourself.


Even though the photons coming from her left eye are the same colour distribution as those of her right eye, you perceive blue.  That blue is as real as any other blue you've ever perceived.

Illusions © Akiyoshi KITAOKA, Professor, Department of Psychology, Ritsumeikan University, Kyoto, Japan - used with kind permission

Checker shadow ©1995, Edward H. Adelson.

Text © Sencillo Press and Gruff Davies 2010

Contact Sencillo

eyecolorconstancycyanLss eyecolorconstancycyanLss blowup

This illusion, and others like it, demonstrate that even a phenomenon as fundamentally 'real' to us such as colour, is merely an interpretation.  Two physically identical sources of light are interpreted as different colours by our brains in different contexts.


2. Checker shadow illusion

Light, shade, brightness and luminosity as we experience them are also 'made up' by the brain.  I never tire of seeing this extraordinary illusion created by Edward Adelson.  The squares labelled A and B appear to be opposite shades on the checker board. They are actually exactly the same shade of grey. The same image on the right has a solid block of grey the same shade showing that the two squares are exactly the same.  

checker shadow - reveal

by Gruff Davies


The boundary between perception and reality is one of the themes explored in The Looking Glass Club, and the idea that reality – at all levels – requires an act of interpretation.  I'm going to use ten of my favourite illusions to explore this further.


There are many levels of 'reality' that we might distinguish, but let's consider three - the social level (or the human world involving others); our personal reality; and physical reality.  


At the social level, we interpret what other people say and do all the time yet live our daily lives as if these are interpretations are real, as if they are 'the truth' about what happened.  ("He forgot my birthday.  He doesn’t love me!" or "My boss hasn't said a word to me today. My email must have upset her.").  Sometimes new facts appear that allow us to change our interpretations enough for us to realise they weren't real in the first place ("A surprise party?!" or "You had a tooth out?").  It's fairly easy to see that reality at the social level is merely an interpretation of events occuring in our personal reality.


Our personal reality is the world as we experience it through our senses.  On the one hand, our senses and perceptions are the only reality we have, yet as illusions can show us, sometimes dramatically, our perceptions are also just interpretations of a physical reality that exists beneath them.


Our personal reality - every experience, every sight, sound smell, colour and taste - whilst it seems perfectly real to us, is an interpretation.  Let's take colour as an example.








Levels of reality

checker shadow letters

(Professor Kitaoka has found a wonderful photo of real world example the checker shadow illusion.)


It's not just colour and shade that our brains construct... [next page]

The following three variants are possibly even more dramatic presented side by side.  In each picture, the iris in the girl's left eye is identical in colour to that of the right.  Yet we see two different shades, and in the third picture two completely different colours, orange and purple!  Again, if you don't believe me, grab these into photoshop and look at the RGB values, or get a magnifying glass.  Left and right eyes in each case are identical.


What ten mind-blowing illusions tell us about reality

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