Weekend Diversion: The Master of Illusions

"Illusion is the first of all pleasures." -Oscar Wilde

It's tough to tell fact from fiction, and sometimes just as hard to tell reality from illusion. As long as you're enjoying yourself this weekend, I'd have to agree with Buckwheat Zydeco, and say

Let The Good Times Roll.

But despite what these images you're looking at might seem to show, there's nothing rolling at all here.

Image credit: Illustrator Fiestoforo. Image credit: Illustrator Fiestoforo.

Nor is anything moving, nor is there a hint of animation in any of these. Yet, based on what your eyes show you, things appear to be bulging, spinning, or more generally, there appears to be motion.

Image credit: Visual artist Anh Pham. Image credit: Visual artist Mark Grenier.

If you look closely, you can definitely see that whatever small section your eyes have honed in on isn't moving, but it's the portion of the image in your peripheral vision that appears to move. And because of how our brains are wired, our attention automatically seeks that out; this is probably a good thing, evolutionarily, for when a predator is stalking you! But that same wiring is what makes these snakes, below, look like they're rotating in your periphery, except for the one you're looking directly at!

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

This optical illusion, above, is no joke; it was made by Akiyoshi Kitaoka, professor of psychology and a researcher of illusions. One of the great illusions he investigated, as illustrated above, is known as the Peripheral Drift Illusion. In a nutshell, our eyes can be tricked by simple changes in luminance, which is why the color-scheme for the rotating snakes was chosen to have a black, a dark color, white, and a light color in that particular sequence. Let's take a look into Kitaoka's investigations.

Image credit: A. Kitaoka and H. Ashida, VISION Vol.15, No.4, 261-262, 2003. Tiling by me. Image credit: A. Kitaoka and H. Ashida, VISION Vol.15, No.4, 261-262, 2003. Tiling by me.

If you put one of these circles, shaded as-is, in your peripheral vision, the light-and-dark shading will make it appear to rotate. I can only see it rotating slowly, and the effect is far from pronounced. But one of the great things Kitaoka has discovered is a way to enhance this illusion. By creating the shading-order as follows: black/dark grey/white/light grey, the effect of the peripheral drift illusion becomes greatly magnified.

Image credit: A. Kitaoka and H. Ashida, VISION Vol.15, No.4, 261-262, 2003. Tiling by me. Image credit: A. Kitaoka and H. Ashida, VISION Vol.15, No.4, 261-262, 2003. Tiling by me.

And by altering the length of the edges, the effect can be enhanced even further!

Image credit: A. Kitaoka and H. Ashida, VISION Vol.15, No.4, 261-262, 2003. Tiling by me. Image credit: A. Kitaoka and H. Ashida, VISION Vol.15, No.4, 261-262, 2003. Tiling by me.

That's what the "rotating snakes" illusion was based off of. But Akiyoshi Kitaoka doesn't just investigate and study illusions and how they are perceived by our eyes, however. He also creates his own, and they are truly spectacular, and appear to trick our eyes in a variety of ways. Here are some of my favorites.

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

Clockwise and counterclockwise rotation, simply by using the altered-length trick.

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

A visual spiral, even though all the "edges" in this picture, above, are completely circular!

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

A central object that appears to move relative to the outer "background," particularly pronounced if you scroll past it!

And a second with the same effect...

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

and a third!

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

Here's one that appears to be blowing in the breeze, even though it's just a stationary background.

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

And here's one where you can see reddish dots at the corners between the tiles, even though the corners are all white!

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

And finally...

I wouldn't call it the evil eye, per se, but it sure does feel like it's sucking me in!

Image credit: Akiyoshi Kitaoka. Image credit: Akiyoshi Kitaoka.

Check out Akiyoshi's home page for literally hundreds of these illusions, and I hope you enjoyed this weekend's diversion! (Oh, and for those of you who get dizzy looking at objects like this, you'll probably get dizzy. I probably should've told you earlier. Oh well.)

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Is there a reason why most of the illustrations don't work on me? I mean the red dot and the heart work, but the others have a faint effect. I ask because I had a stroke a year ago and am mostly recuperated. I walk well, my speech is fine in both my languages and can express myself well, but things like this make me think there is a short still left in my brain.

By German Santanilla (not verified) on 16 Jun 2013 #permalink

The motion illusions only work on me as long as my eyes are scanning around (like normal). If I concentrate really hard on focusing them on one spot the illusion goes away (briefly, since I can't actually keep my eyes motionless long).

So random guess out of the blue: could the stroke have affected eye movement?

I always love these things. Having been a draftsman with high spatial acuity all of my life, I can sometimes ignore the effects. But on the other hand, having spent the 70's and 80's in a lysergically-enriched community of great friends, I say bring 'em on.

I believe staring at works like these trained me to immediately recognize the 3D images in those computer enhanced stereo drawings that were popular years ago. Hmmm. Could you maybe discover some acoustic 3D audio effects to include in a future blog?

By MandoZink (not verified) on 16 Jun 2013 #permalink

I think illusions like this are great, because they teach you that you can't trust your own brain. IMHO that's good training for examining your own assumptions in science. Here's another illusion, which is one of my favourites:


By John Duffield (not verified) on 16 Jun 2013 #permalink

Here's an audio illusion for you.

Take a monophonic audio signal, for example start with a stereo recording but use the left track only, or right track only. Feed that one track into both left and right inputs to an amplifier that's driving a pair of plain hardwired speakers, of the type that you have to connect via a terminal strip at the back.

First, listen to it in mono. Then, reverse the polarity of the connection to the terminals on one of the speakers (either one). Now listen to it again: it appears that the audio image has become "stereophonic," or that its depth has been expanded. This is due to the reversed speaker producing sound that is phase-reversed compared to the normal speaker, and the interactions between the different frequencies of sound under those conditions.

Note, some speakers can be damaged by being connected "backward" (typically those with polarized electrolytic capacitors in their audio crossover networks) so listen at a low volume level to minimize that risk.

For anyone in cog sci or experimental psych, if you're using audio white noise or pink noise in human subject research, try phase-reversing the feed to one speaker (or headphone), and you'll get "depth-expanded" white/pink noise. The subjective sensation of listening to this is substantially different to what you get from the usual monophonic white/pink noise feed.

This is particularly relevant to "sensory deprivation" studies, where white/pink noise is used to provide a uniform audio background. I'm inclined to believe that the difference between mono and expanded white/pink noise will make a difference in the qualitative aspects of the experiences that subjects have in that condition, such that depth-expanded will be experienced as far more pleasant than mono.

Here's another audio illusion: binaural beats.

Connect an audio frequency generator to the left input of an amplifier. Connect a second audio frequency generator to the right input. Using the frequency counters on the audio generators, adjust them so they differ by 8 Hz., for example 200 Hz left, and 208 Hz. right. Adjust the output levels to be the same. Now listen in the headphones at a comfortable volume level.

What you'll hear is a "beat" or modulation, that is the difference between the two input frequencies, in this case, 8 Hz. This audio illusion is produced directly by the brain, as a function of the way the audio processing areas in the left and right hemispheres combine sound from your ears into a normal 3-dimensional audio landscape.

Binaural audio beats can also induce entrainment of brain wave frequencies. For example the 8 Hz. beat frequency I've suggested here, is in the lower "alpha" frequency range, characterized by a pleasant sense of relaxation, but without visual imagery behind your closed eyes. Look up information on the relationship between brain wave frequencies and states of consciousness, and you can experiment on yourself and friends. The "theta" frequency range of 4 - 7 Hz. is particularly interesting, as it's close enough to sleep that it can produce dreamlike visual imagery. Combining different sets of frequencies can be interesting, for example low theta plus high beta to produce a sense of relaxation with alertness.

NOTE: DO NOT experiment with this if you have epilepsy, there is a very slight risk that it could trigger a seizure in the same manner as lights flashing at brain wave frequencies, which range from a fraction of 1 Hz to almost 60 Hz (which also explains why certain types of flickering room lights such as bad fluorescents, can interfere with concentration).

I understand what your suggestions accomplish. I once had some software that would perform alpha-wave transformations to audio tracks but I never tried it. I intended to delve into brainwave feedback experiments, but alas, I never did. For years I designed and built a lot of my own audio processing devices for electronic instruments. All were analog except for a prototype synth-module I made for my violin which dropped the pitch several octaves and allowed me to parse and remodel the waveshape. My roommate and I had an electronics room with oscilloscopes, freq-generator and the like. We routinely high-dosed caffeine, goofed off and breadboarded for hours.

Per your polarity boost/cancel suggestions, I got my roomate to wire up his stereo in his car by adding a third speaker on the dash to sound only the left-right differences (main speakers were in the back). The effect on our favorite music was fascinating. In my own room, I ran the stereo output of my system through a stereo-choruser and amped that to two more corner speakers. The music shimmered, as did I. Those were good times back then.

These days the capabilities of digital processors are remarkable. My DSP effects box does impressive amp, cab and effects modeling. It enables my electric mandolin to create a nice array of blues, jazz, or heavy guitar sounds.

NOTE: My mental aberrations, while undiagnosed, are appreciatively not epileptic in nature.

By MandoZink (not verified) on 17 Jun 2013 #permalink

The black & white ones didn't perform as expected for me, except for the false spiral. That one completely fools my eye, and also tends to twitch cw/ccw randomly. The sequence of medallions with the different shading don't rotate, but the centers strobe in a pretty distracting manner. The yellow/orange and purple/yellow patterns also feature a square that either looks rhomboid, or looks like it is tilted diagonally, even though it's square and level.

@ Ski Bum
I enjoyed the video. Well recorded audio on a nicely set up surround-sound is already quite impressive. People have often expressed doubt that the Universal Translator device on Star Trek could ever work. I always thought that in the future, a well formulated and projected output from a language translator combined with entity position tracking technology could assure each listener would hear only the language intended for them, while cancelling the other peripheral translated sounds.

By MandoZink (not verified) on 17 Jun 2013 #permalink

Re. Mando @ #7: There's a free piece of software by the name of "Gnaural" (from the "GNU" free software license + "aural") that produces binaural beat audio for self-experimentation with its subjective effects. You can program audio sequences for desired outcomes e.g. start at beta, ramp down to alpha for relaxation, or up to gamma for alert concentration.

BTW, this entire field of binaural entrainment of EEG was developed by the Monroe Institute, as a means of reproducibly inducing the brainwave patterns that were found to accompany out-of-body experiences (OBEs). Whatever one believes about the ontological status of OBEs, binaural entrainment is a textbook example of something that starts out in parapsychology and goes mainstream once the mechanism is understood.

Re. the visual illusions on the page here: the one I found most intriguing was the "red dots" example, because unlike the others, it involves an overt hallucination: the perception of objects (the red dots) that do not in any way exist in the image. All of the others involve the perception of movement of objects that do exist on the page. The red dots are wholly synthesized. I'd be very much interested to know how that works, and whether the hallucinated red dots are produced optically by the eyes, or cognitively by the brain's interpretation of signals from the eyes.

Lastly, there are some findings (sorry, I don't have a cite for this) that the signal flow from the optic nerve to the brain looks like random noise, that can't be interpreted by software to ascertain the objects seen by the eyes. If this is the case, it suggests that our normal visual perception is for the most part synthesized by the brain with a high degree of signal processing that utilizes learned examples of objects to organize the input from the eyes. Probably all of us have had the experience of seeing an object or a picture that we can't recognize in even the most generic way, and perceiving the object as nothing more than a collection of shapes and colors. Then once we "understand" what we're looking at, suddenly it "makes sense" and we can assign it to categories and compare to other objects with which we're already familiar.

Pssst...Hey, you. Yeh you. Want some eye drugs?

I am pretty sure that these illusions work because the eye normally moves back and forth in saccades


That movement brings different retinal cells to bear on the pixels that are being looked at. That is necessary to get color vision because eyes do color the way that ccd cameras do, light sensors with differential sensitivity to different wavelengths.

An experiment that you can do to demonstrate that eyes are digital is if you look at a swinging pendulum with both eyes, and then put a partial shade over one eye, the pendulum appears to be going in an ellipse. My interpretation is that cells accumulate signals until they reach a threshold and fire. If it takes longer to accumulate the signals, it will take longer to fire. The later firing cells give a later signal as to when the firing happened, so the object is perceived to be in a different place.

By daedalus2u (not verified) on 19 Jun 2013 #permalink

Your brain wires up the system in ways to inhibit or promote a signal, creating a mental image of a straight line or complete block of colour even though no such thing is detected by the eye itself. The fact you have a huge blind spot but NEVER notice it is a huge pointer to that fact...

And the brain therefore has a hell of a lot to do with what you see: your eyes see almost nothing of what you believe you're seeing.

"Pssst…Hey, you. Yeh you. Want some eye drugs?"

Funny you should say that. Your eye is an excellent delivery route for LSD and its associated psychoactive lysergic acid amides. It is remarkably efficient (only half the dose is required) and response time is quick (10 minutes to onset and only 2 hour to peak, vs 4 hours orally). Also, since eyes are warm, moist and constantly exposed, they have evolved a remarkable defensive chemicals which will immediately lyse (see lysis) most bacteria on contact, so worry of infection is low.

( DISCLAIMER - This is not an endorsement. Do not try this at home.... at least not without Pink Floyd. )

Whoops..., sorry. Another 70's and 80's flashback.

By MandoZink (not verified) on 19 Jun 2013 #permalink

Wow's point (#14) is exactly right, and the key to understanding what's going on. The brain creates these illusions from the raw eyeball-generated signals. And it does so because it's trying to correct for what it perceives as data errors. The brain over time builds up a template of reality, and it tries to show us that reality, even if the signals coming in don't quite fit: "That object shouldn't be moving, or that color; that one should." Drugs can impede or even disable that brain function, leading to pleasant or unpleasant "hallucinations." Decades ago (when I was young and foolish) I took LSD and watched the stucco ceiling above me bubble and churn. But I knew that wasn't really happening, almost immediately the perception changed. I found I could turn it on and off at will. So I asked myself how or why. Then realized I was turning on/off a "filter" in my brain. My eyes were perceiving the stucco ceiling through the waves of heat rising from my own body. In normal mode, my brain smoothed out the signal, telling me, "Nothing to see here; ceiling is not moving." In altered mode, it actually enhanced the perception, saying, "Something funny is going on; that ceiling is behaving very strangely. You might want to get the hell out of here." Now, it's obvious that too much data is coming in from our senses all the time for us to consciously process, so it makes sense for our brains to pre-filter: "Pay attention to this; ignore that" (actually, it doesn't tell us 'ignore that'; it just neglects to inform us of that). But I'm convinced the brain does the same thing in all our functioning, and depending on the rigidity of our preconceptions (or worldview) that can impede our ability to learn, to experience new things, to develop as persons. I'm very glad I took LSD so many years ago -- and learned not to trust my brain. At least not totally.

By chuckinmontreal (not verified) on 21 Jun 2013 #permalink

Re. daedalus2u: Interesting about the pendulum/ellipse illusion, I'll have to try that. (all it takes is a piece of string and any handy small object, and a business card to partially cover one eye).

Re. LSD: The US FDA has been quite a bit more reasonable about authorizing human-subject studies with psychedelics over the past ten years or so. These are usually done with psilocybin, that has a 4 - 6 hour duration of action (compared to 8 - 12 hours for LSD), and the track record so far shows that psilocybin is completely safe under appropriate medical supervision (do not try this at home).

For years I've believed that interesting medical uses for psychedelics will be found at lower dosage levels. The recent finding that Ketamine (a dissassociative anaesthetic with psychedelic properties at sub-anaesthetic doses) is an extremely rapid-acting antidepressant in doses far below the psychedelic dose, supports that conclusion.

The point of this is, drugs such as psilocybin, at doses 1/4 to 1/2 of their normal psychedelic doses, could be highly useful for teaching people new skills involving their perceptual and cognitive functioning. Learning how to turn on/off visual illusions, as chuckinmontreal says, is one example that could prove useful for training people whose occupations involve exposure to novel stimuli, pattern-seeking, and so on. One potential application would be for soldiers who have to deal with camouflaged opponents. Another might be for small aircraft pilots who frequently fly through cloudy or stormy conditions. (Clearly we're not talking about having these people take any amount of psilocybin in their actual work environment, only as an early training exercise to develop a skill that can be used later.)

I will pray for all of you. God Bless.

And I shall give offering for you god botherers.

Satan Guard You.