Here’s a picture to announce a summer posting pause.  We’re working hard on brilliant new features, for a relaunch in a few weeks.  But meanwhile explore the archive – there’s stacks on the site now, and it’s almost all new stuff, not the versions you see on lots of illusion sites.  Try putting the name of any illusion that interests you into the search box at the bottom of the lists to the right.  Or explore popular categories, like Impossible Worlds.  And don’t forget (if you’ve been here before) that there are now nearly a hundred brilliant mini illusions for you to download for your own sites.

This picture is a Photoshop fantasy rather an illusion, but it’s here because I like bubbles. I think the creature is a gecko, (please comment if I got that wrong). The background and sky is from the Nile in Egypt, but I snapped the gecko in the London Zoo. There’s an earlier post on how I photograph the bubbles.  For all the bubble picture posts (and some nice ice) see the category Soap Bubble Pictures.

Just about our first post was a tessellation tutorial. It was quite comprehensive, but a bit heavy going. I’ve been wanting to post an animated demo, because I reckon that seeing that first would make the tutorial much easier to follow. So the animation is below, but first, a reminder of the basics:

A tessellation is a pattern like the one above. The cells of the pattern fit together like jig-saw pieces, with no gaps and no overlaps. You can’t make a pattern like that out of just any old shape. It only works with shapes whose edges can be snipped into pairs of segments with special properties. The two segments in each pair must be indentical, except that they may be either reflections of one another, or rotated in relation to one another, like the hands of an old-fashioned clock. Confused already? Just watch this animation, showing the evolution of the pattern above, and you’ll see how it all works.

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If you can see this illusion, you may be amazed to discover it’s not an animation.  Most people will see waving movement, yet the pattern of lozenges is not really moving at all. But about 5% of people just don’t see this kind of illusion, and if that’s you, it doesn’t mean anything’s wrong. If you do see the movement, it won’t be wherever in the pattern you focus, but in the periphery of your field of view. However, the effect is also very sensitive to size.  I see it vividly with the screen about 15 inches (36 cms) from my eyes, and the image 8 inches (21.5 cms) wide on the screen, but I think you’ll get an even better effect by clicking on the image, if a bigger version then comes up on your system.

It’s a kind of illusion only discovered in the last few years. Lots of discoveries about it have been made by Japanese researcher Akiyoshi Kitaoka, and on his site (amongst scores of other stunning illusions) you’ll find his masterpiece in this line, his famous rotating snakes illusion.

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I’m fascinated by the Poggendorff illusion, and this is a new version of it. (Well, it is according to me.  Others would say it’s a different illusion). I’ve prepared it as an image that can be seen in 3D without a viewer, just to make it more vivid, but you don’t have to view it in 3D to see the effect.  (If you do want to view it in 3D, but don’t have the knack, visit this tutorial).

To see what it’s all about, first check out the figure below:

To the upper left is the classic Poggendorff figure:  the oblique lines are objectively aligned, but the right hand one appears shifted just a bit upwards.  About forty years ago, researcher Stanley Coren showed that the effect persists, weakly, when the configuration is reduced to dots, as at upper right.  But now look at the little array of three spheres to the left below.  I reckon this is a new kind of dot (or sphere) Poggendorff illusion.  Imagine joining up the centres of those three spheres, to make a long, thin triangle, pointing a bit up from horizontal.  Remembering we’re looking just at those three lower left spheres, what kind of triangle would you get?  To my eye, very nearly a right angle triangle.  But now look at the lower right three dots, making up a vertical triangle.  To me they present very much an equilateral triangle.  And yet the relative positions of the dots are identical in the two sets, just rotated to vertical at lower right. For the array lower left to look like a right angle, the target sphere must appear shifted upwards, just like the right hand oblique test line in the traditional, blue figure, immediately above.

It would be great to have comments on whether that works for you, or whether you see both lower arrays as equilateral triangle arrangements – illusions like these often do look different to different observers.

Now try viewing the array at the start of the post. It’s just a multiple version of the array of spheres lower left in the second figure. Check out just the three yellow spheres top right, for example.  If you see it how I see it, the position shifts we see here are like the ones we see in classic Poggendorff figures, but none of the explanations advanced for the misalignment seen in the Poggendorff illusion, including Stanley Coren’s dot version, can easily be applied to these new figures.

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