Illusions (visual, auditory, and more)

I remember seeing plenty of optical illusions of the "these are the same size, but look different because of the surroundings back when I had a working eye, but the font weight ambiguity is a new variant on me… Though to add to the color perception conversation, the exact same spot of color can look orange or brown depending on the background color(I believe it’s the darker the background, the more orange it looks, the lighter the background, the more brown… and I remember seeing an illustration where the apparent discrepency holds up with two identical dots on close, but opposite colored square of a checkerboard(if memory serves, the illustration used white on a medium dark gray for the checkerboard).

And I’ve heard it’s fairly well documented that some optical illusions work better on some people than others, but tsuch claims I’ve heard have usually been in regards to ambiguous image type illusions where people differ on which image they see by default and some people have an easier time switching between the images than other’s. Examples that come to mind are the mask illusion where most people see the outside convex surface of the mask but a minority default to seeing the concave inside of the mask, and the dancer illusion which is just two mirror image frames of a dancer alternating that most people interpret as the dancer spinning which was once believed to be a test for left-brainess versus right-brainess as to whether the viewer saw clockwise or counterclockwise rotation by default… of course, left/right brain dichotomy is discredited.

I can say from personal experience that magic eye, 3-d glasses, the hole in the hand illusion, the 3DS’s top screen, and all other illusions based on binocular vision have never worked on me. Granted, I went blind in my right eye as an infant, so I never had the prerequisite biological hardware for such illusions.


You reminded me of those old stereo images from the 80s that just looked like a bunch on confetti until you stared cross-eyed at it long enough to see the contoured shape of a dolphin. (They never had cool images to see.) :wink:


A lot of these types of illusions are very dependent on presentation, lighting, and setup as well.

If you were to show the Haunted Mansion busts out of context the trick is easily understood,

but when you see them on a set where they are presented in context as normal statues sitting on a shelf and lit correctly to cast the right shadows, it doesn’t immediately occur to you you are seeing an illusion and the effect works better.



@Hal9000: Yeah, that’s the kind of thing I was referring to when I said Magic Eye. Only ever had one working eye, so it was impossible for me to look at anything cross-eyed(or walled eyed for those stereoscopic images where two normal looking photographs of the same subject taken from slightly different angles are presented on a monitor and the idea is to stare at the left hand image with your left eye and the right hand image with your right eyewhile avoiding the usual overlap of visual field. Also, all I ever got out of red/cyan 3-d glasses was a monochrome image of the color of hte left eye filter, all I got of polarized 3-d glasses was dimming the screen and getting rid of the overlapping images, and all I ever got out of the 3DS’s 3-D effect was the screen alternating between bands of light and dark.

@Hanon: Most of the the optical illusions I’m familiar with of are of the the static image printed on a page or displayed on a monitor variety and many rely on lack of detail(often the the images are just outlines or silhouettes, though I think the the mask illusion is one I only heard of after I went blind, though there is one optical illusion(that also crosses over into auditory illusion territory) that doesn’t involve images at all: the the repeated the the illusion, where the brain tends to filter out short, repeated words like the the. See if you can find all the the instances of it in this paragraph.


This is part of the reason it’s often difficult to thoroughly proofread your own work: you’ve seen it so many times it makes sense as is and you won’t notice things like repeated words.

I have also experienced some auditory illusions, such as the Shepard tone, and one where you hear a somewhat degraded recording of a word that will sound like two different words depending on context - often if you see the word printed you’ll hear the word you see, but if they switch the word and play the same sample you’ll hear that word.



Audio pedant interruptus: Actually the Shepard tone is an octave-based tone. It can be used to create an illusion of an unendingly descending or ascending pitch called the Shepard scale. There’s a good quote on the wikipedia page describing the scale as “a musical barber’s pole”.



There’s also an auditory illusion similar to the Shepard Scale, but for tempo, in which the audio loop seems to be getting progressively faster and faster or progressively slower… Sadly, auditory illusions don’t get nearly as much coverage, and other sensory illusions even less so(though I do recall one thermoreceptive illusion exhibit that consisted of three vertically mounted bars, one bar was heated, the opposite bar was chilled, and the middle bar was at ambient temperature.You’d grab the hot and cold bars with a hand a piece and hold for like 15-30 seconds, than grab the middle, ambient bar with both hands, which would feel cool to the hand that held the hot bar and warm to the hand that held the cold bar, at least until your hands return to ambient temperature.

Bottom line, none of our senses can be perfectly trusted


the forever getting faster tempo audio illusion makes me anxious not gonna lie :joy:

another thing abt e-ink. it’s meant to be on a matte screen that reflects light like…a book! e-ink “white” looks off white most of the time.


We in Italy use three basin, two filled with hot and cold water at the sides of a central one filled with lukewarm water. one put one hand, one in the hot and the other in the cold water basin, then put both hands in the central, lukewarm, basin. the hand who was in the hot water feel cold the lukewarm water, and the hand who was in the cold water feel hot the lukewarm water.

(it’s a rare point of contact between science and humanitaries: the experiment explains ancient Latin jokes about the order used in the thermae e.g. “at Rome, people goes from calidarium to tepidarum to frigidum (that is, feeling colder) at Sibari people goes from frigidum to tepidarium to calidarium” (that is, feeling warmer) )

Best regards from Italy,
dott. Piergiorgio.


Something I forgot to mention in my previous post, but I’ve wondered what the brain would think if you played an ascending Shepherd scale in one ear and a descending Shepherd scale in the other… or did the tempo illusion with the accelerating version in one ear and the decelerating version in the other… and if there’s a corresponding illusion for volume(that is, a sound of constant volume, but which seems to be getting ever louder or ever more quiet)… and whether there are any musical compositions that make extensive use of auditory illusions… granted with how little sensory illusions other than optical illusions get talked about, there could be a song I’ve heard countless times with unknown illusions within… The one piece of music with auditory illusions I can name is Endless Stairs from Super Mario 64 which is a Shepherd scale.

ANd yeah, probably myriad ways to setup the hot-cold reversal illusion… After all, many optical illusions are just variants of each other, so its only reasonable to expect the same to hold for other sensory illusions.

Yes, visual illusions can be printed in a book, where auditory illusions require equipment.

The hot-cold bars sensory trick I’ve experienced in more than one museum. In my area I’ve visited The Magic House - back in the day it was much more “magic” but now it’s evolved more into a giant children’s busy box play area for birthday parties, though I believe there are still some of the science illusions. Also the St Louis Science Center is great - last time I was there they had a full-scale Ames room.

We also have a Museum of Illusions that must be relatively new because I’ve just discovered it now. It looks like the real deal, but has the unfortunate URL “moistlouis” (MOI=Museum of Illusions + ST Louis…)


I know only about visual illusions. Or maybe the doppler effect counts as a sonar illusion?

Do you know these strange images where you have to put your nose very close to it and look some time at it and then suddenly a 3D image seems to appear? (This works only with 2 eyes, off course.) It never worked for me! I stared and stared, but nothing happened.

I also love Escher’s drawings. Like the forever up-going walk or the impossible stairs and rooms etc.

1 Like

Brown is just dark orange, so it makes sense varying the background color would change your perception by contrast.

Even with binocular vision, I have never been able to see anything in those 3D stereogram pictures except random colored dots.


The “magic eye” puzzles are subtle and you have to almost be in the right ‘frame of mind’ to see the image. It works on the principle that if your eye is focused on the point in space where the actual image is, you see a repeating pattern. If you cross your eyes so different portions of the separate images from each of your eyes overlap, then relax so that your brain can perceive the overlap as one image with different perspectives in each eye, it can be falsely assembled into a 3D image by your brain. You’re basically doing the work of 3D glasses by aligning two pictures taken from the perspective of each eye together as if your eyes are seeing them separately.

Here’s one that’s a little easier because you can see what it is; there’s no “mystery picture” so you can see what you need to align:

If you cross your eyes (sometimes it helps to stand back a bit so your eyes have less to accomplish) on this picture, you’ll see “four” images, two from each eye.

[image1][image2] [image1][image2]
what you first see with crossed eyes

You want to adjust your focus so the two “inner” images overlap perfectly, either by muscling your focus, or standing a bit away to let your eye relax; if you can get the inner images to align and “lock together” so your brain “commits” to that being your focal point from both eyes, you’ll see a clear 3D image in the center and single 2D images on either side. (You have to commit to the combined center image and focus on it; if you move your focus to look at either side picture you’ll lose it.)

This one helps if you concentrate on getting one of the stars in the image (like the bright one at the top) to align with your eyes crossed.

[image1]  [image2]  =>
      <=  [image1]  [image2]
           3D image

This video is hard and not as convincing to me since it’s moving and way bigger (I had to stand like eight feet back from the screen) but the beginning explains the process you’re doing with your eyes visually.


Thanks @HanonO for the good explanation of the mechanisms in magic eyes (I didn’t know that Magic Eye is the name for it.)

EDIT: I tried it with the method you gave (concentrating on the middle picture) and for the first time in my life it worked. (Both with the star nebula and the title picture of that video! :slight_smile:


I’ve tried many times over the years, and again with your examples. It just doesn’t seem to work for me.


I think “Magic Eye” is the patented name for those pictures with the mystery image. The difficulty in Magic Eye is you’re not sure where where the focus is, and they deliberately make the texture of the picture different. It may be random kaleidoscope or watercolor or repeating images that may show you a dolphin shape hovering in space, but since it has that unrelated texture, it can be difficult to know what you’re looking at. I think that’s the point of those puzzles. But once you understand how it work you at least have a chance to decipher them.

This one is quite difficult - it looks like several mashed up images of fish, but if you Magic-eye it, the layers separate so each different color/type of fish is split to a different layer on the Z-axis.

The difficulty is you’re not aligning two discrete images, but you’re searching the alignment point, all while not knowing what you’re supposed to see and trying to make your eyes do something they’re not used to doing (choosing a different focal point than where the actual image is.)


Yes, you are right. The examples found in magazines don’t have the clear separation into two pictures. But from the two-image examples I learned what to do with my eyes.

I have large occlusions in the retinas of both my right and left eyes. I have to be very careful not to let my brain fool me. My visual processing does its best to fill in the blank areas. I can totally miss an object that truly exists. The blank fill just blend with the surrounds making the real object disappear.


Day one of epistemology class we were shown this classic illusion:


A and B are the same colour! I remember the student next to me saying “If this was a religion, I’d be converted”. I guess we were being inoculated against naïve realism.