Illusions and insights

The clearest example of the active nature of our perception is probably the existence of many illusions that can fool us. You probably already have witnessed a few, and you probably have seen yourself some stunning example of pictures where «there’s more than meets the eye».
Although this is not the most important example nor the most important reason why we need to understand better the nature of our mind, this is an excellent place to start to become familiar with the idea.

There are also some artworks that exploit these principles, the most famous of which are probably «Swans reflecting elephants» by Salvador Dalí and much of the works by Escher, who is especially known for making impossible pictures, illusory scenarios and art that challenges the fundamental nature of our perception. Images with less artistic value and designed to simply illustrate the illusion in question, however, may be even better to make us understand what is going on. Some of them are well known, and you may often notice them while surfing the web. Especially popular in these days seems to be «double images», often disguised as personality or intelligence tests. These are pictures that you can interpret in at least two completely different ways.

You probably have seen already, for example, the illusion of the old woman that can also be seen as a young one looking to the side, or the one where two faces looking at each other create a vase in the white background (here on the right).

I think the word «illusion» is a bit misleading in situations like this. That’s because it may suggests that the image contains a «correct» meaning along with an «illusory» one. In reality, however, there is not such a thing. It doesn’t make much sense to ask which interpretation is the correct one. In fact, if you think at it, it doesn’t even make much sense to think there is a meaning whatsoever. All you really see in a picture is a set of spots and lines. Even when you look at a photo or a realistic portrait of something, you are merely seeing a combinations of coloured dots on bi-dimensional surface. There really is no «object» in it. Any time you look at a picture and you realize what is in it, you are creating a meaning in something that, inherently, has none. Now, you may think this is a bit flawed reasoning. The image is supposed to have a meaning since, say, the artist had disposed the lines and dots precisely in such a way to convey a specific meaning. Still, however, this is possible because the artist’s perception happens in similar fashion to our own, and they are themselves creating a certain illusory meaning from the inherently non-sensical elements they draw or paint.

This may seem a complex and counter-intuitive statement, so let’s see a second example to make it more clear. You probably have seen as well some images that convey the illusion of movement: spirals, grids, or other pictures where, when we move our eyes across it, the elements around seems to move. And so on. Once more, you have an illustration of this on the right. That is clearly a static image on a printed page, so it can’t possibly be moving. Still, however, your eyes are telling something very different, aren’t they? You may say, then, that you are seeing something that is not «real». But is this the most meaningful way to describe what is happening? Sure, the movement in the spiral is not an objective property of the world. You can say you are being «fooled» into perceiving something that is not real. However, this implies that while looking at the image something unusual is going on. And that’s not the case. Technically speaking, the movement in the image above is not any different from movement you perceive at any other moment. In a sense, it is just as real – or just as not real, however you like to say it – because at any moment the perception of movement happens in your brain as a response to certain clues of the visual stimuli you are receiving.
This doesn’t meant that there is nothing objective outside your head. We already dismissed the evil demon hypothesis on practical grounds. However, the Subtle Evil Demon may still be there. Although there is an objective reality outside, you only see part of it. After that, the Subtle Demon fills the rest and tells you what the «outcome» looks like (i.e. is something moving or not).

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What you perceive, ever, is only what the Subtle Demon tells you about the real world. Whether the movement is an objective property of an external element or not, the reason you perceive something as moving is because your own brain decides so, based on a few clues it is actually observing. In most cases these clues are informative of what is really going on outside our head, of course. But sometimes they are not, like in the image above where a certain disposition of the lines triggered the response «something is moving», although such thing is not happening. To reinforce this point, notice that you can’t «unsee» an illusion, even after you know about it. You knew all the time the image above was not really moving, didn’t you? Still, although you know, you keep seeing the movement. This is commonplace with «illusions». It’s not that your brain is «tricked». It’s simply how your perception works. You can’t «decide» that you will not perceive the illusion any more than you can decide you will not perceive a real object in front of you.

An other famous example of illusion uses a chess board with some parts are under shadow. Although the shadowed white squares end up being of the very same colour of the black squares being directly under the light, we keep seeing them as a different colour (the white square still being lighter). You can clearly see that’s not the case by covering all of the image aside one shadowed white square and one enlightened black square. In such condition, you realize they are both the same colour. If, however, you remove the obstacle again, you start once more seeing the white square as being lighter, although you perfectly know that’s not the case. The same principle has been used to create images where our three-dimensional depth perception using shadows is exploited to make us see squares with the same colour as being very different. Here you can see an other example which works in a very similar way, although without colours since this books is printed in black and white.

In this image you can spot the illusion by covering with your finger the area between the upper and lower part. Before you do so, the shadows are telling you where there is more and less light, and you therefore perceive one side as being of a lighter colour than the other. However, after you covered the middle part where the two figure touch each other (which is the clue telling you there are two different figures altogether, rather than a single element), you can see that the two colours are exactly the same. To many people it looks like magic to see how the colour switch from being different to being the same as you move the finger on and away the separation point. The real magic, however, is in perception itself, being a very complex although instantaneous extraction of meanings from few cues we are often not aware of. Once more, notice how it is improper to say your vision was «tricked» into believing something not real. All you can say is that your perception tells you things that are not real, since it may reach opposite conclusions in different circumstances. But any perception is just as consistent as the other, and you can’t stop seeing something you realized to be illusory.

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This post is a free excerpt from my book.

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