The Great Bowerbird is a curious bird. The males spend most of their time building bowers, which are elaborate structures, constructed solely for attracting females. These loveshacks are decorated with stones (and sticks, bones, etc.) in a very specific way: Small stones are put near the entrance of the bower; Larger stones are put further away. When looking out from the inside of the bower, which is were the females stand during courtship, this arrangement leads to a striking distortion of perspective. You can see this in the image below (compare b to c). In a sense, the size gradient of the stones flattens the image, reducing the subjective perception of depth.

Photos from Kelley & Endler (2012) and Anderson (2012)

The male bowerbird is quite picky about this arrangement. If the size gradient is disturbed (by a biologist, for example), the males immediately restore it. But why? Since the purpose of the bower is to seduce females, it is tempting to speculate that the distorted perspective is aesthetically pleasing to female bowerbirds. Who, as mentioned above, tend to stand inside the bower as they watch the male perform his dance of seduction.

But there could be numerous other explanations. For example, the males could simply be too lazy to carry big stones all the way to the bower. Or something like that.

But no, it appears that the distorted perspective really is what matters. In a recent issue of Science, Kelley and Endler investigated what the perfect size gradient is …

The following illusion is a variation on the boogie-woogie illusion, described by Patrick Cavanagh and (yes, again!) Stuart Anstis. If you play the video and track the moving dot with your eyes, you will see that the edges of the diamond shape come to life. Specifically, the dots that make up the edges appear to travel along the lines. Kind of like the steps of an escalator.

So what might be going on here? I have to admit that my degree of belief in the explanation that I will outline here is modest. But that being said, here we go: Essentially, this illusion could be an instance of the aperture problem.

Imagine that you are looking through a hole, as in a in the figure below. Through this hole, you can see part of a bar, but not all of it. Now imagine that the bar moves, as in b, c, or d. Can you tell, based on what you can see through the hole, what the exact movement of the bar has been? No! As long as you cannot see the ends of the bar, all three forms of movement look the same.

So what do people perceive when presented with this type of ambiguous motion? Well, they tend to perceive a motion that is orthogonal to the length of the object (d). Perhaps we are biased to perceive orthogonal motion, because that's how objects generally move (do they, though?). Or perhaps it's because orthogonal motion is, in a …

I recently came across this awesome optical illusion, first described by Stuart Anstis. Two bars, one red and one blue, move horizontally across the display. If a specific type of background texture is present, the two rectangles appear to move in anti-phase: When the red rectangle moves quickly, the blue one grinds to a halt, and vice versa. This is illusionary, of course, and the effect is gone when the background texture is removed.

The two rectangles resemble a pair of stepping (or shuffling) feet, hence the name: the stepping feet illusion. (The effect is strongest for some people if you don't look directly at the rectangles.)

The explanation for this illusion appears to be fairly straightforward (but see [1]). And, as any good illusion, it provides some insight into how our visual system works.

The crux is that the illusion will not work with just any pair of colours: There must be a luminance difference. Put differently, one stimulus must be bright (the blue rectangle in this case) and the other must be dark (the red one). In addition, there must be a comparable luminance difference in the background, which is achieved here through a pattern of alternating light and dark bands.

Now, let's say that the front and hind edges of the stimuli are on a dark band, as in a) in the figure below. In this situation, there is little contrast between the side edges of the red stimulus and the background (both are dark). Because of …

Oxford University Press, 2011 (Paperback)

Conclusion From turbulent rivers to auto-catalytic chemical reactions. With the "Nature's Patterns" trilogy, Philip Ball gives us an eclectic, yet surprisingly coherent overview of all kinds of patterns that are found in nature. It's an interesting and challenging read, but perhaps a single book would have sufficed.

Why are honeycomb cells hexagonal? Why do spotted animals tend to have striped tails? And, for that matter, why are animal pelts so often spotted or striped, rather than endowed with, say, a rectangular grid? Why does Jupiter have a giant red spot?

The diversity of the issues that Philip Ball takes on in his trilogy on nature's patterns is overwhelming. Most of them cannot even be said to have much in common: Jupiter's red spot cannot be explained in the same way as the shape of a honeycomb cell. Yet, despite his eclectic subject matter, Philip Ball manages to tell a coherent story. One that goes far beyond stamp collecting of interesting factoids.

A recurring theme in the three books (Shapes, Flow, and Branches) that together form Nature's Patterns: A Tapestry in Three Parts is that many patterns are 'emergent properties'. Spotted and striped pelts do not necessarily provide the best possible camouflage, so they cannot be fully explained in Darwinian terms. Nor is it practical (even if perhaps theoretically possible) to explain such patterns in terms of the laws of physics. Instead, Ball argues, to explain why spots and stripes are so common, you need to …

When writing a scientific paper it is considered good style to convey an absolute and unrelenting trust in your own findings. So in many papers the discussion section starts with something like 'the present study is the first to conclusively show that (...)' or 'the results clearly show that (...)'.

I've written a few lines like that as well. But, tainted with hypocrisy, I actually find this style of writing a bit weird. It is no secret that cognitive science is a messy business, and that experimental data is seldom clear-cut. Most scientists, and certainly the good ones, are quite frank about this. So why the sudden attack of confidence when writing a paper?

Well... I don't know, and perhaps it is just a matter of style without any real reason. Fashion, in a sense. But it does strike me that this is a relatively new phenomenon, and that scientists in the past were much more equivocal in their writing. The quite recent past, even. Take, for example, Michael Posner, who wrote in the abstract of his seminal 1980 paper Orienting of Attention that '(...) the possibility is explored that (...)'. Or Giacomo Rizzolatti, of mirror neuron fame, who wrote back in 1987 that '(...) the hypothesis is proposed that postulates (...)'. Both of these sentences (which were of course cherry-picked for the occasion) convey a modest degree of belief in ones own theory and/ or findings: I believe in X, but I could be wrong.

I thought it would be cool to analyse the PubMed …