Optical Illusions » Geometric illusions

The Twisted Stairs (version 2)

david — Fri, 15 Jan 2010 15:28:39 +0000

I’ve been wanting to do a new version of my earlier post of The Twisted Stairs. That’s partly because the way I placed the figures in the original posting, they got in a bit the way of seeing the twist in the lateral flights of stairs. I reckon you can see the twist effect better [...]

80 Illusions Poster

david — Wed, 09 Dec 2009 17:06:20 +0000

You’re welcome to download and use for private purposes any of the imagery on the site, except for a very few pictures where I indicate that third party copyright might apply. But if you’d like a giant, 35 x 23 inch poster, full of illusions, you can buy it (along with loads of illusions on [...]

Doggendorff and Moggendorff Illusions

david — Tue, 08 Dec 2009 17:15:35 +0000

Here are a couple more variants of the Poggendorff illusion (mog, or moggy, by the way, is a term of endearment for a cat in UK English, but I’m not sure it’ll be familiar if your background is in American English). The symmetry axes of the dog and cat heads are objectively aligned, but to [...]

Pinna’s Intertwining Illusion

david — Sat, 05 Dec 2009 12:55:37 +0000

This is a brilliant illusion discovered by Baingio Pinna of the University of Sassari in Italy. The circles appear to spiral and intersect, but are in fact an orderly set of concentric circles. The illusion is due to the way the orientation of the squares alternates from circle to circle, and that contrast alternates from [...]

Subtle misjudgments of horizontal and vertical

david — Sat, 28 Nov 2009 11:24:31 +0000

Back in 1987 James Walker and Matthew Shank in the university of Missouri were doing a study of the Bourdon illusion. In some figures they devised for comparisons in their study they noticed a new effect, quite unrelated to their study. The figure upper left is a version of their chance discovery. The centre line [...]

Shepard’s tables – What’s up? (post no. 3)

david — Fri, 23 Oct 2009 17:35:31 +0000

This is a third look at the Shepard’s tables illusion. If you didn’t see the earlier posts, you might like to get up to speed on the illusion by scrolling down two posts to an animated demo. The two pairs of table-tops in these views are absolutely identical, and within each pair the two lozenge [...]

Shepard’s Tables – what’s up? (post no. 2)

david — Sun, 18 Oct 2009 10:47:34 +0000

The previous post presented an animation of Shepard’s Tables. If you didn’t see that, you might want to check it out first (scroll down to the previous post) to get the basics of the illusion. This new version of the illusion, with nested tables, follows the pattern: all eight of the lozenge shaped [...]

Shepard’s Tables – what’s up?

david — Wed, 14 Oct 2009 09:40:29 +0000

This is an animation of Shepard’s Tables, an illusion first published by Roger Shepard as Turning the Tables, (see his wonderful book Mind Sights, 1990, pages 48 and 127-8). The left hand lozenge-shaped table top seems to get longer and thinner as it rotates, but it’s an illusion. It [...]

An Ocean Wave Illusion

david — Sat, 06 Jun 2009 10:30:18 +0000

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 [...]

Dotty Poggy

david — Tue, 02 Jun 2009 14:24:16 +0000

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 [...]