Perceptual Illusions (2018) | Hacker News Reader

Perceptual Illusions (2018)

nautil.us

150 pointsrobertwiblin34 comments

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.

https://yewtu.be/watch?v=S4IHB3qK1KU

It reveals that at least this aspect of feline and human visual perception appears to be similar.

As a means of getting inside a cat's head, it's never failed to fascinate me.

There's another ... perceptual phenomenon is probably a better description than illusion ... 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.

In my case, I'd started listening to the podcast whilst falling asleep. I don't recall consciously hearing the cue ... but ... when I replayed the podcast the next day, I could understand the audio clip on the first play. I'd "crossed over to the other side* without even consciously hearing the cue.

(I've looked for the episode in the archives listing. I cannot find it though I think it may turn up.)

https://youarenotsosmart.com/all-posts/

Found it, episode 103, "Desirability Bias"

Mind, after several months of not having heard that episode ... I understood the audio immediately.

Audio: https://youarenotsosmart.com/wp-content/uploads/2017/07/103-... (mp3)

Episode: https://youarenotsosmart.com/2017/07/20/yanss-103-desirabili...

When David McRaney says "savour that feeling, because there is no going back", believe him. There really isn't.

The clip, and the reveal, are at the beginning of the episode.

Funny, I was able to wring some sense out of it on second hearing just because I was primed to expect that there was something there. But it turned out not to be quite the right answer. Now that I have heard the big reveal, I can actually hear it both ways, my original, (slightly) mistaken interpretation, and the actual answer.

But it occurs to me that this is exactly how humans learn language. We start by hearing an idealized version, carefully enunciated by parents and primary school teachers, and then we generalize that to more sloppy, noisy renderings in real-life situations, movies, podcasts...

So this experience is reproducible in the large: listen to a foreign language. It's noise. Then learn that language and it stops being noise and takes on meaning. Like the small example, ee efshar lachzor yoter lahatchalah. (That's a latinized transliteration of a Hebrew phrase. Figuring out what it means is left as an exercise :-)

bill / pail / mayo

https://yewtu.be/watch?v=KiuO_Z2_AD4

Similar to sibling comment, I understood what the noise was immediately, but I have no way of knowing if it's because I was primed by your comment.

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're convex and do not when they're concave. You can see this if you lay the tip of your mouse pointer over them.

Check out http://illusionoftheyear.com/

It's a yearly contest with people coming up with various stuff. Normally one finds Kokichi Sugihara in the top. I'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: https://github.com/Matsemann/impossible-objects

https://github.com/Matsemann/impossible-objects

holy crap those gifs with the mirror are completely doing my head in

http://www.ritsumei.ac.jp/~akitaoka/index-e.html

These 'Illusions' 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.

And its not just those 'Illusions'.

In reality, whatever that is, there aren't any vanishing lines meeting at a vanishing point somewhere around infinity.

But that 2D graphical user interface in your head comes in handy, moving in a higher dimensional (mostly 3, sometimes 4) reality.

So since perception is always subjective illusion (are there any others), science in a sense is parting from Illusions.

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't trust our eyes / senses for a lot of things! Some people should figure out a way for us to figure out what's true or not, even though we can't see what's true or not. /sarcasm

That's why eye witnesses aren't as reliable as one might think

I'm wondering if anyone has used optical illusions as a way to screen for bots.

what's the rate of a given illusion working consistently across general population? Probably not high enough to make that approach work.

> 3. Confetti

> 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.

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 less green, not more.

I’m pretty sure the effect just comes from half-toning.

>If the apparent difference was due to perceiving the lines as a neutral surrounding

That's not how it works.

https://www.livescience.com/confetti-munker-white-optical-il...

Another example

https://www.sciencealert.com/crazy-optical-illusion-makes-yo...

Agreed, I experience exactly the same, and is the weakest (read: most easily understood) example shown.

The others are all very good, I really like that I can understand why I am perceiving them the why I do, but despite of that can’t “fix” that perception.

Discussed at the time:

Perceptual Illusions - https://news.ycombinator.com/item?id=18307428 - 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 regularly go on 10+ mile hikes with my girlfriend and we’ve noticed this happens after 2-3 hrs of straight, continuous hiking. When you all the sudden stop, it looks like the surrounding environment is coming at you. Super weird, same concept.

Less impressively, the same effect can be observed after playing Guitar Hero for a while.

It's amazing how well it reproduces how some psychedelics warp vision. Those act on the brain, this tricks the eyes, similar result.

I experience something similar while cycling on trails. If I watch only the road rolling under me for some time and then look at some static object, like a big cloud, it appears to move towards me (or away, can't remember right now).

Nos. 3 and 4 only work at some sizes. If you increase or decrease the size of no 4, the illusion goes Away. For no 3, if you size up, the illusion goes away (as the bleed stops being an issue)

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's a 2013 article about the interaction of alpha rhythms in the brain and a flickering wheel illusion:

https://www.jneurosci.org/content/33/33/13498#:~:text=The%20....

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't I ever perceive actual Tube trains as going backwards? Or indeed ordinary mainline trains?

I suspect that the illusion/gif is ambiguous because it's made of just two repeating frames. A "smooth" version of it with more frames would reveal the real direction of the train.

Because you can see lot more than like... 3 frames or whatever it is that gif has; plus you have other cues, like the wind, sound, ground vibrations.

It's interesting to compare the effectiveness of these illusions when your sober and when you'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've often wondered if there are perceptual illusions for blind people: Maybe a physical cafe wall would feel like the rows weren't parallel.

There's a neat one that involves touch called the Thermal Grill Illusion. You put two pipes together and run cold water through one and warm water through the other. It feels scalding hot when you grab them.

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's different. I have to read the explanation to understand what other people are seeing.

Maybe you are a bot

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