You think she is looking at you from across the room? But then when you speak to her, you think it must all have been in your mind. It may not be in your mind, but in your eyes - an optical illusion! Or so the runner-up for this year’s Best Visual Illusion of the Year Contest showed.
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Who hasn’t, as a child, sat for hours making trees dance by alternatively closing an eye? Some people retain that fascination for life, and the Best Visual Illusion of the Year Contest brings them together with results that might change the way you look at the world.
The competition is a fantastic coming together of science and art, and makes learning about optical illusions fun.
Visual illusions are those perceptual experiences that do not match the physical reality. Understanding visual illusions is an important part of the process of curing many diseases of the visual system. Therefore – and here’s a fabulous job! – there are visual scientists dedicated to discovering the neural underpinnings of visual illusionary perception.
The 2008 winners, Rob van Lier and Mark Vergeer from the Netherlands, portrayed an illusion that shows that the colour viewed induces an aftermath of diluted colour on a surface that is actually white. This is a well-known phenomenon, but the edge they showed is that 'a coloured image can produce different coloured after-images at the same retinal location”'(Lier & Vergeer). Click below and try it out:
Filling in the after-image after the image
What to do
Fix your gaze on the centre of one of the figures, and stare at it for some time (20-30 seconds) while it cycles (without moving your eyes).
After several iterations you'll start noticing that the empty outlines fill in with ghostly reddish or bluish colours. These are called "after-images".
Interestingly, the colours of the after images vary, which is puzzling because they come from the same original figure. Moreover, the shape of the outlines determines the filled-in colour, which is complementary to the colour of the same shape in the original figure.
Lier and Vergeer explain that the perceived after-image colours depend on the contours presented after the colour image. But more specifically, the illusion shows that the after-image colours spread and mix between those contours.
'The phenomenon is likely to be caused by a spreading of the after-image of those elements between the physical contours of the outline shape,' they say. 'For example, when a circle is positioned in the centre of the outline shape, no after-image is perceived within the circle.
'In conclusion the observations are due to a rapid spreading of local patch-based after-images within the outlines presented after the image.'
Ghostly gaze
The “Ghostly Gaze” by Rob Jenkins was runner-up. This is the “you- think-she’s-looking-at-you-but-it's-all-an-illusion”, illusion:
Ghostly Gaze.
What to do
Move the slider and watch how both women turn their eyes to you.
We normally try and figure out where someone is looking by perceiving where the dark parts of their eyes are looking. Jenkins shows that details such as the outline of the iris can override larger patches of darkness.
We take many social cues from a gaze direction, and Jenkins’ Ghostly Gaze illusion shows “gaze estimation is not always dominated by gross luminance distribution across the eye”. So make sure she really gave you the cue and looked at you before you act, guys!
Hollow mask
The third prize awarded to Thomas Papathomas from the US added an additional illusion onto the well known hollow-mask illusion.
Have you ever had a mask hanging up and been sure that its gaze follows you as you walk in front? In addition when the hollow mask is made to rotate, it appears to turn opposite to the actual direction it is in fact rotating.
Now if we add an object such as a nose ring, it is not assigned the illusionary depth that the mask does. This in effect creates a motion illusion as the object appears to rotate in the opposite direction to that of the mask (you may have to download a programme in order to see this image):
Hollow Mask
Building & clouds
An additional illusion that the competition explains answers why the contours of skyscrapers appear to bulge against a cloudy sky. Most illusory distortions of parallel lines disappear if contours are jagged.
However, in Bettella, Casco & Roncatos’ illusion, the illusion is still present, irrespective of the jagged contours, because, “the visual system relies on local luminance contrast to code local tilts and positions along the contour bordered by a thin outline”.
This broadening of the illusion landed Bettella, Casco & Roncatos’ in the top 10. Check it out:
Building & Clouds
Shaded arch
Here’s one for artists. Dejan Todorovic, who won third prize in 2005, displays an impossible object with a shaded arch. Our vision interprets shading differently, according to the shape of the contours.
In this image, two different contours are shaded with the same pattern, but convey two different reliefs. This reveals how the optical system reacts when faced with ambiguous input:
Shaded Arch
Pinball Wizard
Michael Pickard’s illusion, the Pinball Wizard, causes a sense of optical rotation. The interesting thing about this popular illusion is that it breaks the ‘rules’.
Whilst the classic Rubin-vase illusion demonstrates how we automatically segregate foreground and background in an image, the Pinball Wizard shows a single image acting simultaneously as both images.
This gives rise to an illusory sense of rotation. Using visual cues to create an impression of depth and carefully chosen colour values, a static screen is combined with an animation of horizontally traversing spheres.
The screen appears simultaneously as a background and as foreground surface on the spheres - inducing a sense of rotation as the spheres move (you may have to download a programme in order to see this image):
Pinball Wizard
(Claire Latouf, Health24, July 2008)
To find out more about illusions, or to enter 2009’s Best Visual Illusion of the Year Contest, go to Illusion contest.
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