Optical illusions are like magic, thrilling us because of their capacity to reveal the fallibility of our senses. But there's more to them than that, according to Dr Beau Lotto, a neuroscientist who is wowing the scientific world with work that crosses the boundaries of art, neurology, natural history and philosophy.

What they reveal, he says, is that the whole world is the creation of our brain. What we see, what we hear, feel and what we think we know is not a photographic reflection of the world, but an instantaneous unthinking calculation as to what is the most useful way of seeing the world. It's a best guess based on the past experience of the individual, a long evolutionary past that has shaped the structure of our brains. The world is literally shaped by our pasts.

Dr Lotto, 40, an American who is a reader in neuroscience at University College London, has set out to prove it in stunning visual illusions, sculptures and installations, which have been included in art-science exhibitions at the Hayward Gallery, the Serpentine Gallery, the Cheltenham Festival and, most recently, the new Science Gallery at Trinity College Dublin. His latest creation, The Beacon (see facing page) is about to be unveiled on the pavements of Old Street, East London .

He explains his complex ideas from the starting point of visual illusions, which far from revealing how fragile our senses are show how remarkably robust they are at providing a picture of the world that serves a purpose to us. For centuries, artists and scientists have noted that a grey dot looks lighter against a dark background than the same grey dot against a light background. In the same way, colours appear different according to what colour they are next to. Why? The conventional belief was that it was because of some way the brain and eye is intrinsically wired. But Dr Lotto believes this is wrong.

He says it's a learnt response; in other words, we see the world not as it is but as it is useful to us. His optical illusions seek to demonstrate this by proving that there are all sorts of ways you can make same-coloured areas look different, not just what colour they're against. You can produce similar effects with the way we perceive shade and form too.

His illusions throw in a whole range of visual clues that prompt the brain to draw conclusions about the objects we encounter on the basis of past experience. Look at the green and red tables right. They appear to have different dimensions, with the green table much longer and thinner. In fact, as the second table picture shows, their dimensions are virtually identical. The yellow line shows that the width of the green table is the same as the length of the red table. The blue line shows that the length of the green table is the same as the width of the red table. Why are we so deceived?

What is happening is that our brain is taking into account all the visual clues it has learned over a lifetime. Our brains have learnt to estimate size in a useful way, by the way objects sit in space, rather than according to a “pure” measurement. We have learnt to use all sorts of cues, such as light, shadow and the laws of perspective, to assess the nature of things. In three dimensions, these clues will help us perceive a table in a practical way - so that we don't fall over it, for example. But when the real world is represented in two dimensions, all that “useful” learning can deceive us. Dr Lotto observes the peculiarity of such illusions: our brain can simultaneously recognise it is being fooled, while being unable to see the illusion any differently.

“Context is everything, because our brains have evolved to constantly re-define normality,” says Dr Lotto. “What we see is defined by our own experiences of the past, but also by what the human race has experienced through its history. The structure of the brain is a reflection of that history.”

What Lotto means by this is illustrated by the fact that different cultures and communities have different viewpoints of the world, conditioned over generations, an area that neuroscientists are just beginning to unpick. For example, Japanese people have a famous inability to distinguish between the “R” and the “L” sound. This arises because in Japanese the sounds are totally interchangeable.

“Differentiating between them has never been useful, so the brain has never learnt to do it. It's not just that Japanese people find it hard to tell the difference. They literally cannot hear the difference.”

Dr Lotto is convinced that his experiments are grounding more and more hypotheses in hard science. “Yes, my work is idea-driven,” he says. “But lots of research, such as MRI brain scanning, is technique-driven. I don't believe you can understand the brain by taking it out of its natural environment and looking at it in a laboratory. You have to look at what it evolved to do, and look at it in relationship to its ecology.”

Street sculpture

Dr Beau Lotto's latest sculptural creation,The Beacon, will be unveiled on the streets of London next month. The installation, on Old Street, in Shoreditch (see the artist's impression above), demonstrates our relationship with our environment, with lights showing how colour is affected by its context, and with innovative powering arrangements showing how human beings are dependent on their surroundings for heat and light.

The six metre steel tower, funded by the Shoreditch Trust and Transport for London, incorporates solar cells and 16 fluorescent lights behind different colours of Plexiglas. By day it will cast the light of the sun into coloured shadows on the pavement. By night, stored solar energy will illuminate the energy-efficient lights.

Dr Lotto has invented special paving slabs made of photovoltaic cells and recycled glass to harvest sunlight and to help power the structure. He has applied for a patent.

Learning from busy bees

The Bee Matrix, by Dr Beau Lotto, pictured here at Trinity College Dublin, is a sculpture based on experiments investigating the way brains learn to perceive the world.

It's the result of a series of tests on bees, carried out in a glass box (see below left). Along one wall of the box are 64 illuminated lights, the intensity and colour of which can be changed. Each light also contains a glass tube that can be filled with nectar.

Dr Lotto wanted to see if bees could learn a concept such as “the darkest”, irrespective of colour and, if so, how quickly. The 64 lights were adjusted to random colours and various light levels. But only the darkest light was primed with nectar.

Special sensors tracked the movement of a bee each time it was admitted to the box. Dr Lotto found that, at first, the bee flew randomly. Several attempts later, the bee flew straight to the darkest tube, even if it had moved. They had learnt the concept of darkest because it was useful. Dr Lotto says that the learning process took two minutes.

The electronic recordings of the bees' flightpaths documented their learning process, and Dr Lotto had the bee trails etched by laser into glass cubes, piling the cubes up into towers, (main picture and below right) each tower representing the two minutes of time.

Visual cues that cause shady cube confusion

Dr Beau Lotto's visual illusions deal with our perception of colour, form and brightness.Look at the upper and lower surfaces of the object in the first picture (far left). They look different shades: white below, dark grey above. In fact, the colours of their surfaces are identical. This is demonstrated in the second picture (left), where all but two small circles on the top and bottom surfaces have been masked off, revealing that their colour is the same.

It's hard to believe, so convinced is our brain that the colours are different. What's happening is that our brain is taking into account all the visual clues it has learnt over a lifetime to distinguish the nature of objects. Normally, shadow on the ground tells us that light is coming from above, so the lower object must be in shade. Our brain compensates for this and tells us the colour of its face is lighter than it really is. The bright edge caught in the light is another trick that seems to confirm this.

“The more you increase the probability of something being in shadow, the more the illusion increases,” says Dr Lotto. “The brain isn't seeing the world as it is, but it has generated a useful image that can prompt behaviour to respond.”

In this case, the brain has developed a way of seeing based on the usefulness of being able to distinguish things in shadow, something that might well improve your ability to survive.

DOWNLOAD MORE ILLUSIONS

BRIGHTNESS ILLUSIONS

1. The large cubes in the foreground appear very different in brightness, but a mask reveals that their surfaces are identical. Download

2. The browns in this example appear completely different in tonal value, yet they are physically identical. Download

COLOUR ILLUSIONS

3. Despite what appears to be a fundamental difference the blue tiles on the left hand cube are identical in colour to the yellow tiles on the right hand cube – and all are grey. Download

4. The white tile under the table is identical to the black/grey tile to the right. The surrounding colour makes us see it otherwise. Download

FORM ILLUSIONS

5. The angles created by these four objects appear widely different, yet all are a perfect 90 degrees. Shading and colour give this effect. The red object appears to create a obtuse angle while the green object appears to create an acute angle. Download

Visit lottolab.org for more illusions from Beau Lotto

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