Illusion and reality


The artist begins with a vision – a creative operation requiring an effort.
Henry Matisse

What do you see in the picture accompanying this article? The answer will probably be: «two dalmatian dogs, sitting and looking at the front»; you might even have the impression that they are staring at you. But they are nothing but black spots over a white background. Nevertheless, if you only see a bunch of black marks, start worrying and consult a neurologist. The dalmatians are a fabrication of our brain as a result of an extremely complex process of visual perception. We constantly receive external and internal information (from the world in which we live and from our own body), which our brain interprets in a split-second, giving meaning to it. The perception process is very creative, involves a large part of our brain and is learnt. Many will surely think: «no one taught me how to see, I was born with that ability». We learn to see during childhood, through experience in the visual world, combining information from different sensory modes, completely unaware. Without that experience, we cannot «make sense» of the information that travels from the retina (the sensory part of the eye) to the brain. We know this through visual deprivation experiments in animals, but also thanks to the study of people who were born blind or lost their sight at a very early age and recovered it as adults (after a cornea transplant, for instance). They are not able to calculate distances, or integrate different elements of an object to make sense of it. They would not perceive the dalmatians, only the spots. They live in an often frustrating world between blindness and vision.


The need to «learn to see» exists due to the nature of the stimulus and the design of the system. The information sent by the retina to the brain is inherently ambiguous. The image of a large and distant object projected in the retina can be identical to that of a small nearby object. An object projects very different images depending on its orientation. The reflected wavelength we perceive as colour changes depending on the chromatic characteristics of the light that reaches the object, and the same happens with the intensity of reflected light. Usually, what we perceive is far away from the reality that can be measured with rulers, lasers and photometers. Visual illusions are the clearest evidence of the dissociation between physical reality and subjective perception. When we experience an illusion, we can see something that is not there, not see something that is actually there or see something different than what is really there. The disconnect between reality and perception causes visual illusions to be interpreted incorrectly by the brain when it recreates the physical world. Some researchers defend a reinterpretation of the biological significance of visual illusions and what they reveal about perception. Visual illusions represent configurations we have in our everyday life that let us interpret the world in which we live. In the example on the margin, we perceive square A as lighter than square B, despite the fact that they are exactly the same shade of grey. Our brain quickly calculates probabilities based on prior experience with lights, shadows and checker-boards, to conclude that probably A is a white square in shadows and B is an illuminated black square. That is the most likely possibility.

«The way we perceive the world is not actually real, but it is useful for us to perceive it that way»

Animal survival depends on the ability to adjust their behaviour to their environment. Therefore, evolution should have favoured the ability to obtain reliable information from our environment. We tend to think that reliability depends on the precision of measuring instruments, but the most reliable information is not necessarily the most accurate. The possibility to perceive the world differently from physical measurements indicates that, rather than deceiving us, it helps us to interact. The way we perceive the world is not actually real, but it is useful for us to perceive it that way.

© Mètode 2015 - 87. Online only. On the origin of life - Autumn 2015

Serra Húnter Associate Professor of Psychobiology of the Department of Experimental Medicine of the University of Lleida (Spain) and member of the «Brain Development and Evolution» Research Group of the Biomedical Research Institute of Lleida (IRBLleida). Her research career focuses on the study of animal behaviour and its biological basis, especially on the relationships between brain, behaviour and evolution.