• Science
    Optical illusions

    The deceptive brain


    Do phenomena such as The Dress or a 3D painting on the sidewalk leave you flabbergasted? Sometimes, your brain draws hasty conclusions, says neuroscientist Whee Ky Ma at Studium Generale on Monday, 18 January.
    By Christien Boomsma / Translation by Sarah van Steenderen

    Who would have thought that Whee Ky Ma – at 22 one of the youngest PhD students in the Netherlands, ever – would leave his career in physics? Yet the former resident of Groningen chose to focus on neuroscience after obtaining his doctoral degree. On Monday, he will be visiting from New York to talk about his favourite subject: optical illusions.

    Amazing 3D paintings on the sidewalk, a castle that is in black and white but looks like it is in colour, and The Dress: all illusions that you fall for every time, even when you know how the trick works. They are fun to look at and be amazed by. But for Ma, who is currently a professor of neuroscience and psychology at the University of New York, there is more going on. Mindfucks like these say a myriad of things about human perception. Such as what? Ma will explain this during the kickoff of the lecture series Weet wat je ziet. Over perceptie, illusies en hersenen (Know what you’re looking at. Perception, illusions, and the brain), at Studium Generale.

    The checkershadow illusion

    Square A and square B are the exact same shade of grey. And yet you could swear that A is much darker than B. That is because of the column on the picture. Your brain ‘knows’ that the column should be casting a shadow and therefore interprets the picture that way. This illusion was designed in 1995 by Ted Adelson at MIT.

    Ma combines his background in mathematics with his interest in psychology. ‘Human behaviour can also be codified into laws’, Ma posits with certainty. ‘Not in the same way as the laws of Newton and Einstein, but you can apply equations to it and make reliable predictions about the way people are going to behave.’

    Black box

    He is not talking about predictions about buying a new car or bicycle, but rather our reaction after the quick – often subconscious – analysis of the world around us. How, for instance, do we perceive traffic? And what do we do with the uncertainty about that perception when it is foggy? ‘The brain is a black box’, says Ma. ‘Things go into it and come out again.’

    The Spanish castle

    This is one of Whee Ky Ma’s favourite illusions. Stare at the picture of yellow and blue splotches for thirty seconds. When you then look at a black and white picture of a castle, you can see it in colour.
    You do not, incidentally, need the theory of prior knowledge to be able to explain this illusion. In this case, the colour comes into being because the colour-sensitive cones in your eyes become overstimulated. When the picture is lost, the balance shifts to the complimentary colour. So yellow becomes blue, red becomes green, and blue takes on a yellow tint.

    That subconscious analysis also plays a part in optical illusions, says Ma. While most internet sites concentrate on separate explanations, he would rather look for an explanation that covers all the bases. ‘With an optical illusion, the brain actually does exactly the same thing it always does’, he says. ‘You see something, your brain goes over all the possible explanations for the signals at lightning speed, and then picks one.’ And all that happens in a fraction of a second.

    So when you come upon a 3D street painting of exposed pipes, if you stand at the right spot and close one eye to prevent depth perception, your brain can choose one of two different interpretations: either this is a strangely deformed painting or it is a three-dimensional image of a familiar object. ‘Your brain will choose the most likely option. Prior knowledge is very important in this choice – and that knowledge is based on a lifetime’s worth exposure to images and objects.’

    The Dress

    Black and blue or white and gold? You would think the two are easily distinguishable from one another, and yet…
    The explanation partly has to do with how the viewer judges where the light on the dress is coming from. Are you assuming that it’s morning light because you happen to be more of a morning person? Then you probably see the dress as white and gold. If you presume evening light, you will interpret the image differently.

    Early birds and night owls

    This strategy plays a role in almost all human perception and explains a majority of the well-known visual illusions, Ma reiterates. Take, for instance, the internet hype surrounding The Dress last year. After a blogger put a picture of a striped dress on her Tumblr, it turned out that approximately half the people saw the dress as black and blue, while the other half saw it as white and gold. How was this possible? ‘The different interpretations may have to do with where people assume the light is coming from’, Ma explains. ‘People who are night owls often see the dress as black and blue, while morning people see it as white and gold. Night owls experience light differently than early birds and that can influence the interpretation of the image.’

    Breaking free from these illusions is difficult, and in some cases even impossible. ‘The strategy your brain uses is very effective’, Ma confirms. ‘As it should be. You have to be able to rely on that automatic method. What if you doubt everything you see? It would make it really difficult to safely cross the street.’

    You can hear all about The Dress and other illusions during Studium Generale. Other lectures in the ‘Weet wat je ziet‘ series will be held on 26 January, 2 February and 9 February.

    McGurk effect

    Watch this man, and listen to him. No doubt about it, right? He is saying ‘bah’. And then? Then he is saying ‘fa’. That is what your brain is telling you, anyway. But in reality, the sound is the same: ‘Bah.’ But your brain disregards this information when it sees the lips moving differently. Only when you close your eyes can you hear the ‘real’ sound again. So with a ‘b’.