Optical Illusion: What do you see, zigzags or curves?

Originally published at: Optical Illusion: What do you see, zigzags or curves? | Boing Boing


I see curves for both types of lines on the black and white backgrounds, but in the gray background, I get the zig-zags (even though my brain totally knows they are the same as the lines). Does that make me partially curve blind?


That’s exactly how I see this ‘illusion.’ Since cataract surgery in 2016, I went from practically blind myopia, astigmatism and presbyopia to 20/30 hyperopia, still with astigmatism, just not as pronounced as before the surgery. I wonder if the astigmatism is what makes me “curve blind?”


This is a bit silly, really. The zig zag curves are clearly more angular and are only elliptical right where they change direction. Even if they were solid black on a white background I would still have called them zig zags. These optical illusions are fun to gauge how your brain processes subtle visual variances, but certainly nothing authoritative enough to declare “blindness”.


What do you see, zigzags or curves?



I see both at the same time; and if you stare at it for long enough, you start to see spirals… everywhere!


Oh you see a vase? Must be awful going through life with human face blindness!


Funny I see zig-zags everywhere.


That’s a really dumb “illusion”

Do you see a straight line? Hah! Its actually a circle of infinite radius, n00b!

ETA: okay, only where there is a sharp transition at the peaks and troughs do the curves transform into zigzags. That seems like a reasonable shortcut by my brain. Thanks brain, keep up the good work!


When I look at it I see the curves with the color discontinuity at the peeks/troughs as zig zags on the grey background, but curved on the white or black backgrounds, but I see the other curves with the color discontinuity in the ‘strait’ section as curves on all three backgrounds. To satisfy my self I downloaded the image and opened it in gimp to do some editing and confirmed that the curvature on the lines is the same regardless of background or color pattern.

I do agree that trying to label this as a blindness is unnecessarily … hyperbolic.


salvador dali said he saw rhinoceros horns throughout everything he saw. i regard that description as an early recognition of the fractal nature of reality.


This is bunk, honestly. You aren’t ‘curvature blind’, you’re actually seeing the lighting of something that is angled sharply. It’s just applied to something that is curved.

I’ve done amateur texture work for 3d modelling for years, and when you are working in low-poly environments the artistry comes down to fooling the eye. Low-polygon models are blocky, angular, unrealistic even when they are supposed to be graceful curves.

So what do you do? You make a high polygon model, bake the texture, and then put the same texture on the low poly model. The baked lighting from a smooth, nicely curved object fools the eye into seeing that shape, and ignoring the actual topology of the model.

That is what is being done here. Don’t look at the actual shapes, look at the implied lighting on the lines. Sure, the lines are curved, but the transition between highlight and shadows from the ones that fool you are sharp, as if they were zigzag shaped.

You aren’t curvature blind, you’re just seeing something that wouldn’t ever really be real in the first place. Those curves wouldn’t have those highlights in reality. They’ve just been applied to fool you.


curve blindness? that’s unfair - its just context. Put the slightly curved line up against a field of true zig-zag and it will stand out.


Right, I get that. What I was saying that, even seeing the curvature of the zig zags and perceiving the difference between backgrounds, I would still have called the zig zags zig zags. Unless zig zag was defined as having straight lines that zig and zag at angles and are not elliptical, it’s highly subjective.

Also, it doesn’t prove anything other than that some people have more difficulty than others at distinguishing subtle variance amongst varying visual noise. Or maybe difficulty isn’t even the right word. People perceive things differently, which is hardly earth-shattering info. This makes me think of “36 Signs You Are in Love — The Millenial Way” quizzes in Cosmo (and yes, that’s an actual title I just looked up; so much stupider than I expected).


I’d be more impressed if the lines weren’t so thin and the radiuses so small.

also what’s with the audio? why is it even a video in the first place? either I’m old, or this is kind of dumb

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no - the radius in both types of lines is the same - the difference is where they change from dark to light.

The ones that look curved change tone at the mid-height, which empasizes the curve at the peaks and troughs.

The ones that look zig-zag change tone at the peaks and troughs, so the curve segment in each tone goes through the transition from curving one way to curving the other, which tends to cancel out to your eye, making it look like straight segments.


I think the illusion becomes more noticeable if you were to have a high resolution version of it.

@aLynHall explained it well. It really is a trick of lighting. Here is a snip from the top left were I increased the sharpness and turned the gray white. It’s the blending of the gray in the middle that tricks the eye into seeing what is not there. If we are all seeing the same thing I wouldn’t call it blindness.



Wow… some folks sure have taken this topic seriously.


I see zig zagging curves…
I also see glasses that are twice the size needed…

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That IS the illusion; the “zig zag curves” are the exact same shape as the “circle curves”; they are just shaded differently.