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Today I saw an optical illusion that I absolutely loved, to the point that I actually fired up IDL and generated my own set of animated gifs for this blog. Look at these two dots:

It’s easy to see that they are completely in phase and always the same colour. If we now place a big black border around one point and a big white border around the second point then something incredible happens:

The colours look like they’re completely out of phase, but really both of the dots are always the same colour as each other! No I don’t expect you to believe me. Yes you can go and check in Photoshop (or by hiding the image with a piece of paper then cutting two holes where the changing circles are). Here is a quote from Shapiro et al (2004), where this effect was first published:

The effect arises, in part, because of the conflict between the luminance and contrast signals. If our perception tracks the luminance level of the disks, then the disks should appear to be modulating in phase; if our perception tracks the contrast signal, which arises at the edge, the disks should appear to be alternating. Because at low frequencies both aspects can be perceived, the effect indicates that at a relatively late stage of visual processing, the signals that originate from the center of a patch of light can be separated perceptually from signals that originate at the edges. (p. 460)

This boils down to there being a conflict in the brain between the changing luminescence of the patches, and the contrast around their edges. Whatever it is, my mind is pretty much 100% blown

found via (Mixing Memory)

Contents of this post under the

You know those optical illusions where you spend ages staring at a random blob and then all of a sudden a hidden picture jumps out at you, like this one:

I keep noticing a similar thing in real life. After noticing a concealed detail in a design I just can’t unsee it, and then for ever more I just fixate on that one little feature. The archetypical example of this is, of course, the Fed Ex logo:

In the negative space between the last e and the x there is a perfectly formed arrow. If you weren’t aware of it before you’ll now start seeing that very clever little bit of graphic design in every single copy of the fedex logo from today onwards.

I’m now going to blow your mind with this one:

This is, the logo of the Islamic Republic of Iran (as an aside, I wish we had a logo as well as a flag). Now, if I add just three dots to the logo:

IT IS A PENGUIN WITH A MOUSTACHE, WEARING A BLACK TIE. Ever since learning that Iran’s official logo is a cheerful cartoon penguin my appreciation for them has increased tenfold.

Labels: opticalillusion

Warning! The following post may cause any and all monocles you are wearing to be ejected violently from your face as your eyes bulge in incredulity.

I often write about incredible optical illusions (part 1,part 2). This is another of those posts. We have all seen the illusions where you are asked to stare at a single colour for 30 seconds, which tires out some of the receptors in your eyes. You then see some weird effects when looking at a different image.

This takes it to the next level.

Additionally the author teaches you how to make your own version of this illusion in Photoshop!

Labels: opticalillusion

Back when this blog was but a wee young thing I talked about optical illusions ( here), and discussed for a while about how our minds have a terrifyingly strong filter between the ‘real world’ and the simplified version of reality our conscious mind works with on a daily basis (see old post for more detail).

I had nearly forgotten about how freaked out Iused to be about this until I saw this image:

^{Clicky for big. If somebody could find out who the origianl author is I’d appreciate being told as I just found this image on my hard drive!}

The central crossbar (X) shaped junctions are the same colour in each of the two structures. I still don’t really believe it, but have checked for myself with photoshop. This one picture serves as a horrible (or wonderful, I guess it depends on how you look at this sort of thing) reminder that the way we see things is coloured by what they are surrounded by. This really serves as a stark reminder that it is exactly the same mechanism that lets us know that a bright white reflection from a piece of coal is actually black, or that a table we see in low-light conditions is actually bright red that make our brains fill in the gaps in completely the wrong way here.

Although I know intellectually that my conscious mind couldn’t handle being bombarded with every single piece of infomation my senses recieve and that it absolutely must make some shortcuts and assumptions to operate in everyday life it still scares me to have it driven home like this.

Labels: opticalillusion

If I wore a monocle it would seriously have popped straight out of my eye when I heard this mp3 and if my mental state could be summed up by a picture it would probably be this one:

The mp3 is just that cool. Put on some headphones (note the headphones bit is important, this will not work with speakers) and enjoy the most awesome 3d sound experience ever:

awesome mp3 here

This technique is called holophonic sound and is described much better by some random page on the internet than I could ever manage:

Developed in the 1980s by Hugo Zuccarelli, Holophonic Sound uses the same "multiple exposure" premise as that used to create holographic images (“holograms”). Holophonic Sound is produced by recording the interference pattern generated when the original recorded signal is combined with an inaudible digital reference signal. The recorded sound produced is so realistic, some people claim they can smell sulphur when they listen to a holophonic recording of someone striking a match! It appears that Holophonic Sound waves stimulate our brains to reproduce very realistic and truly three dimensional sound within us, thereby stimulating other corresponding responses that our brains expect to accompany the sound, (like scents or other sensations). Even more interesting is the fact that researchers report that some hearing impaired people can “hear” Holophonic Sound - again because it stimulates their brains even though their audio receiver mechanisms are not working properly.

How completely and utterly fucking awesome is that?

Wiki link here

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I love finding odd mind tricks and have put them in the blog pretty extensively (optical illusions, and weird neurological tricks)

Here’s another that I stumbled over today, the McGurk effect.

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A while ago I got interested in the question: ‘do there exist patterns or pictures that can cause actual physical pain to view’. I can’t remember exactly why this question seemed to important, but I’m sure everybody will agree that it is a fun one to ask.

At the time there existed a website (sadly dead now) on which the existence of these pictures was confirmed and a single reference given: Computers and the Imagination by Clifford Pickover. Sadly this book is out of print at the moment but I managed to grab a second hand copy off eBay, where I found the following quote:

In 1984, several British researchers discovered that some people find a certain pattern of stripes painful to look at; moreover, stripe viewing apparently induced headache attacks in some subjects

Awesome! I knew immediately that I had no choice but to find this picture and stare at it until my eyes melted. Thankfully Mr. Pickover gave a reference to a journal article in which the picture was reprinted:

Wilkins, A. et. al. (1984), 'A Neurological Basis for Visual Discomfort', Brain, 107:989-1017

Oh my, this is in the University library! Not only does it include a description of what the image looks like:

a circle filled with alternating black and white stripes. At a viewing distance of 43cm, this grating has a spatial frequency of 3 cycles/degree of visual arc, and a Michelson contrast of about 0.7

but it is reproduced in full on the second page!

The picture in the paper was pretty uncomfortable to look at, and after ten or so seconds I turned my eyes away due to a really unpleasant ’swimming’ sensation.

Recently I found a reproduction of the image on the internet (here it is!), unfortunately the size of the stripes depends strongly on monitor resolution, so for me this image did absolutely nothing.

Obviously you should probably not click the above link if you suffer from migraines or are epileptic.

I want to know now why this picture is so hard to look at.

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Optical illusion time!

Here are a couple of examples that have caught my eye recently, the first one you have probably seen before but it’s bloody impressive anyway. The two labelled squares are exactly the same colour (check in photoshop if you don’t believe me)

The second one is a little more obscure:

The two parallelograms are actually exactly the same size. I still have a hard time believing it. Click here for an interactive demonstration that they are the same. I first stumbled across this second one reading about human perception, here is a short explanation of how it works.
Objects stretching away from the viewer get foreshortened by projection, and the brain compensates for this, so we tend to see a given distance running up-and-down in the visual field as coming from a longer objectrunning left-to-right. And that makes us see the lengths and widths differently in the turned tables.

–Steven Pinker (in The Blank Slate)
It’s quite interesting to note that although our eyes are pretty bad at determining relative brightness (the shadow picture) and relative shape (the table picture), by the time we consciously percieve either one of the images our brain has filtered the input through a kind of ‘real life filter’ and has made the shadow appear darker and the table appear smaller. It’s very interesting to think about exactly how much filtering the brain does, and the lies it can tell us.

p.s. I’m back in Durham as of now so I’ll see most of the people who actually read this at work tomorrow. Thanks to the Room311 blog for keeping me up to date with various and sundry going ons in the department during my absence. Look forward to a return to daily (or more) posts in the near future.

Labels: opticalillusion

This is probably one of the weirdest optical illusions I have seen recently, (full explanation on this page).

Go and stare at these two grids for a few minutes. Yes, a few minutes, don’t rush this, it’s worth it.

When you’re done staring at the grids come back here.

If you look at the black-and-white grid again, you should notice a green haze around the horizontal lines, and a magenta haze around the vertical lines. The intensity of this effect varies between individuals. If you don't see this, go gaze at the colored grids for a while longer.

I know what you are thinking: this is a simple afterimage effect. If you think so, walk away from your terminal until you think the after image should be gone. Go home and try it in the morning. Then take a look. Or better, simply rotate the image.

I love this effect because it’s not just your eyes getting exhausted by one colour but rather something actually taking place in the brain:

The effect typically lasts for hours, or even overnight. The duration can be changed by the consumption of coffee and other psychoactive drugs. One paper found that it is stronger in extroverts than introverts, and might be a reliable test for extroversion.

The precise cause of the effect is unknown, and currently under investigation. It is not a simple case of fatigued neurons: there are neurotransmitters involved and appear to be responsible for the long-lasting nature of the effect. It probably takes place in the V1 processing stage of visual information. This is the first image processing after the signal leaves the retina in the eye. The edge detection circuits somehow become associated with the color. At this stage the processing is monocular: the images from the two eyes have not been combined.

I first looked at the grid about a week ago and can still see the haze. Weird.

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