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Eyestonishing Notes for Teachers and Home Educators

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Eyestonishing Notes for Teachers and Home Educators EyeStonishing Notes for Teachers and Home Educators The activity starts with a consideration of the biology of the eye; how it functions and how our brains interpret the messages. Understandably this is kept brief but interested children can easily research this topic themselves. Firstly, it is important to emphasise that the medium being used – the internet – might not show illusions to best effect. If viewers are using a tablet or mobile phone, the screen will be too small for peripheral vision effects. If the screen resolution is low, again effects might not be demonstrable. We therefore include all the images in high definition for you to download and examine. Experience shows that simply copying these high-resolution images into a simple App like ‘Paint’ and displaying them on a big screen is effective. Now, some science …… Our brain and eyes work so well together that we believe what we are seeing is correct but our visual organs (eyes and brain) can sometimes be fooled into seeing things that aren’t there or incorrectly seeing things that are there. These effects are called optical illusions. Many illusions are created because we don’t see objects on their own. Instead we see them in context and surrounded by other objects which can influence our vision. By playing around with the context of colours, shapes, and tones and by changing the viewpoint of the audience you can create a wide range of illusions that will have you questioning what is real and what is not real. Video 1 Here an introductory section talks about the eye and vision. It moves on to consider: Scintillating Grids • Dark circles / blobs appear at the point where the white lines cross on the grid. Staring at one central white dot will leave your peripheral vision seeing black dots. • The mysterious blobs only appear when the crossing lines are straight, vertical and horizontal. When this happens the contrast between the lines and the black spaces creates a lateral inhibition effect. This occurs when signals from photoreceptors in your eyes conflict with each other, creating the impression of dark blobs where the white lines cross • Your eyes and brain use contrasts between light and shade to define the shape of objects. Your ability to see in 3D depends on how light and shadow are laid out. When you see a surface that has differently lit areas your visual system enhances the contrast to see it more clearly. This is called lateral inhibition and it works so well that it can create a lot of powerful visual illusions. Motion • Your eyes are so sensitive to light and motion that, sometimes you see movement even when there isn’t any. This is because your eyes make tiny movements that you are not aware of. When you look at an image you do not actually look at it in a steady way. Instead your eyes constantly jerk around, locating interesting parts of the scene to builds up a mental ‘map’ of the whole picture. Scientists call these random eye movements ‘Saccades’. • As your eyes try to follow the patterns, they make tiny movements, switching between the lines and the colours. This tricks the brain into seeing movement where there isn’t any. • This effect will not be apparent on a small or low-resolution screen. • Pulsing Star o The pulsating (right below) may be caused by differences between your central and peripheral vision. Your central vision is sharper and more sensitive to colour while peripheral vision is more sensitive to motion. The difference can create illusions of movement. • In a spin o As your eyes try to follow the patterns, (left below) they make tiny movements, switching between the lines and the colours. This tricks the brain into seeing movement where there isn’t any. 3-D Stereo images • Stereograms (also known as ‘autostereograms’ or ‘magic eye’) are 3D images hidden within a 2D pattern. In order to see the 3D image, move your face nearer to the screen. At this distance, your eyes cannot focus on the image and they focus somewhere behind the image. Now slowly move away from the image while trying to keep your eyes out-of-focus until you see the hidden image. Seeing a stereogram is tricky and you may have to be patient because it can take a little time. • The first stereogram is of a butterfly, then a DNA helix. In the garden it looks like a crocodile! While a bear is centrally located in this one. The bear looks like it is sat in a box or on a window sill. • These 3D images have all been easily visible on a computer screen – with a bit of practice. Surprisingly, they have been hardest to see when the You Tube videos have been shown in full screen mode. Video 2 Impossible shapes and Impossible Art • Impossible Cube Note how parts of the cube seem to be simultaneously in front of and behind other parts of the cube. You will see something which appears physically possible yet which you know is not. • Impossible triangle Follow the shape of the triangle starting at the top point; note how the left side seems to extend away from you, and the right side seems to extend towards you, yet they seem to lie on the same plane when they reach and are connected by the bottom vertices. You will see something which appears physically possible yet which you know is not. The shape of the triangle might at first appear feasible, but upon reflection one can see that it would be physically impossible to construct such a shape. • The Ambiguous Ring is one of many impossible figures (or impossible objects or undecidable figures): it depicts an object which could not possibly exist. It’s impossible for the Ambiguous Ring to exist because in order for it to exist rules of Euclidean geometry would have to be violated. Look at the green surface: is it the front or the back surface of the ring? You should experience a sense of perceptual confusion as you note the paradoxical nature of the depicted ring. • The Penrose Stairs Figure was created by Lionel Sharples Penrose (1898 -1972), a British psychiatrist, geneticist, and mathematician, and his son Sir Roger Penrose (1931 -), a British mathematician, physicist and philosopher of science. It was first published in the British Journal of Psychology in 1958 The Penrose Stairs is an impossible figure (or impossible object or undecidable figure): it depicts an object which could not possibly exist. It is impossible for the Penrose Stairs to exist because in order for it to exist rules of Euclidean geometry would have to be violated. For example, if one were to complete a circuit of the stairs, one would end up back at the same level that one began, even though each flight of the stairs continuously rise (or fall, depending on the direction of travel). Note how the stairs appear to continuously ascend when tracing round their path in one direction and descend in the other, yet if one were to complete a circuit one would end up back at the same level that one began. You will see something which appears physically possible yet which you know is not. • Belevedere is a painting by Maurits Cornelis Escher (1898 - 1972), a Dutch graphic artist that contains many impossible figures and impossible elements. The print was created in 1958, and the original version is now in the National Gallery of Canada, in Ontario. Look at the paradoxical placement of many of the pillars - look at where they begin at the top and where they end at the bottom, and yet they appear vertical. Look also at the impossible placement of the ladder. And notice the impossible cube that the boy sitting outside of the building is holding. You should experience a sense of perceptual confusion as you note the paradoxical nature of the building and other features in the painting. Bigger or Smaller? And Lining Up: How long? How far away? How much? We measure distance and estimate the dimensions of objects all the time usually without thinking about it. We can usually tell the difference between the actual size of an object and its apparent size. The actual size of an object cannot be observed (but it can be measured), because it must be viewed from a distance so that your eyes can focus on it. The apparent size of an object depends on it size and how far away it is. Objects that are closer will appear larger than if they are further away. Perspective and size constancy also play a part in how we see things. They obey these simple rules: • For two objects with the same ACTUAL size, the one that looks bigger is thought to be closer. • When we see two objects with the same APPARENT size, the one that appears to be further away is thought to be larger. • Muller-Lyer Illusion: Look at the two horizontal lines; note the apparent difference in length difference. The top horizontal line (with arrow heads pointing outwards) should appear to be longer than the bottom horizontal line (with arrowheads pointing inwards). However, they are in fact the same length. The Müller-Lyer Illusion is named after its creator, Franz Carl Müller-Lyer (1857 - 1916), a German psychiatrist and sociologist, who first published the illusion in the physiology journal Archiv für Anatomie und Physiologie, Physiologische Abteilung in 1889. The Müller-Lyer Illusion is one among a number of illusions where a central aspect of a simple line image – e.g.
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