Perceptual Illusions (2018)

One of may favourite instances of an optical illusion ever is this short video of a cat pouncing on a sheet of paper on which shows an apparent-motions spirals illusion.<p><a href="https:&#x2F;&#x2F;yewtu.be&#x2F;watch?v=S4IHB3qK1KU" rel="nofollow">https:&#x2F;&#x2F;yewtu.be&#x2F;watch?v=S4IHB3qK1KU</a><p>It reveals that at least <i>this</i> aspect of feline and human visual perception appears to be similar.<p>As a means of getting inside a cat&#x27;s head, it&#x27;s never failed to fascinate me.<p>There&#x27;s another ... <i>perceptual phenomenon</i> is probably a better description than <i>illusion</i> ... contained in an episode of the You Are Not So Smart podcast. In it, a short snippet of noise is played. It sounds completely random. After a cue is heard ... the noise resolves to a comprehensible message.<p>In my case, I&#x27;d started listening to the podcast whilst falling asleep. I don&#x27;t recall consciously hearing the cue ... but ... when I replayed the podcast the next day, <i>I could understand the audio clip on the first play</i>. I&#x27;d &quot;crossed over to the other side* without even consciously hearing the cue.<p>(I&#x27;ve looked for the episode in the archives listing. I cannot find it though I think it may turn up.)<p><a href="https:&#x2F;&#x2F;youarenotsosmart.com&#x2F;all-posts&#x2F;" rel="nofollow">https:&#x2F;&#x2F;youarenotsosmart.com&#x2F;all-posts&#x2F;</a>

Number 8 has not been created correctly. The line segments actually are being lengthened and shortened because the black segments overlap part of the colored line when they&#x27;re convex and do not when they&#x27;re concave. You can see this if you lay the tip of your mouse pointer over them.

Check out <a href="http:&#x2F;&#x2F;illusionoftheyear.com&#x2F;" rel="nofollow">http:&#x2F;&#x2F;illusionoftheyear.com&#x2F;</a><p>It&#x27;s a yearly contest with people coming up with various stuff. Normally one finds Kokichi Sugihara in the top. I&#x27;m a big fan of him after meeting him at a conference (FUN With Algorithms), and made my own attempts on some of his concepts: <a href="https:&#x2F;&#x2F;github.com&#x2F;Matsemann&#x2F;impossible-objects" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;Matsemann&#x2F;impossible-objects</a>

<a href="http:&#x2F;&#x2F;www.ritsumei.ac.jp&#x2F;~akitaoka&#x2F;index-e.html" rel="nofollow">http:&#x2F;&#x2F;www.ritsumei.ac.jp&#x2F;~akitaoka&#x2F;index-e.html</a><p>These &#x27;Illusions&#x27; that trick the mind are based on perceptional biases, more or less hard-coded brain structures that gave its ancestors a survival advantage. They had faster reaction times with some out-of-the-box categories and such. They back-propagate information that filters perception.<p>And its not just those &#x27;Illusions&#x27;.<p>In reality, whatever that is, there aren&#x27;t any vanishing lines meeting at a vanishing point somewhere around infinity.<p>But that 2D graphical user interface in your head comes in handy, moving in a higher dimensional (mostly 3, sometimes 4) reality.<p>So since perception is always subjective illusion (are there any others), science in a sense is parting from Illusions.<p>Something, one or the other religion, strangely also claims for itself.

Very nice collection. All the illusions are due to natural intelligence in the days of artificial intelligence. Brainpower is always a mystery to me.

Wow, that means we really can&#x27;t trust our eyes &#x2F; senses for a lot of things! Some people should figure out a way for us to figure out what&#x27;s true or not, even though we can&#x27;t see what&#x27;s true or not. &#x2F;sarcasm

I&#x27;m wondering if anyone has used optical illusions as a way to screen for bots.

&gt; 3. Confetti<p>&gt; The illusion is a vivid demonstration of the fact that we don’t directly perceive the colors of objects in the world. Instead, the perceptual system takes an educated “guess,” based on the objects’ surroundings.<p>I disagree. E.g. the circles overlapped with green and blue lines look greenish to me, and the circles overlapped with purple and blue look pinkish. If the apparent difference was due to perceiving the lines as a neutral surrounding, the effect should be the opposite: a circle overlapped with green should come across as <i>less</i> green, not more.<p>I’m pretty sure the effect just comes from half-toning.

Discussed at the time:<p><i>Perceptual Illusions</i> - <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=18307428" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=18307428</a> - Oct 2018 (24 comments)

Number 12 is quite something, it works with anything you look at after staring the center of the top image. I looked at my food and I could see it moving in a very odd manner, went back to image for 15 seconds and looked at the walls, same effect and repeated the same with other stuff and after 10 minutes I feel motion sickness like the one you get after spinning and losing your balance (not everyone gets this I think)

I wonder how many of these illusions work in 3D. Might have to take a crack at modelling the rice wave illusion or the cafe wall illusion for 3d printing.

Here&#x27;s a 2013 article about the interaction of alpha rhythms in the brain and a flickering wheel illusion:<p><a href="https:&#x2F;&#x2F;www.jneurosci.org&#x2F;content&#x2F;33&#x2F;33&#x2F;13498#:~:text=The%20flickering%20wheel%20illusion.,the%20afterimage%20of%20the%20stimulus" rel="nofollow">https:&#x2F;&#x2F;www.jneurosci.org&#x2F;content&#x2F;33&#x2F;33&#x2F;13498#:~:text=The%20...</a>.

These were all great. I have a question on the Tube train one though - as someone that has lived over 20 years of his life in London, a lot of them using the Tube, why don&#x27;t I ever perceive actual Tube trains as going backwards? Or indeed ordinary mainline trains?

It&#x27;s interesting to compare the effectiveness of these illusions when your sober and when you&#x27;re fairly drunk...

My favorite perceptual illusion of all time is the Rauchenberg Illusion: a pure white canvas, when observed intently, is anything but pure white.

I&#x27;ve often wondered if there are perceptual illusions for blind people: Maybe a physical cafe wall would feel like the rows weren&#x27;t parallel.

I seem to be immune from most of these illusions. I am not color blind and both my eyes can see fine. It must be something inside my head that&#x27;s different. I have to read the explanation to understand what other people are seeing.