The Bourdon Optical Illusion

Bourdon Optical Illusion
Bourdon Optical Illusion

There’s a new optical illusion in town, and its name is “Bourdon Illusion“. The Bourdon  illusion is the apparent “bentness” of the straight edge of a figure consisting of two elongated triangles arranged apex to apex.

Like you see in the image on your left, the upper side of the left-lower triangle is actually aligned with the upper side of the right-upper triangle, the former appears to tilt counterclockwise while the latter clockwise. What we are seeing here is “seemingly bent” type of illusion. But why?

Further, I’ve added three rather subtle illusions, each showing bent lines. In Bourdon’s illusion, to the left, the straight left hand edge looks bent again. In Humphrey’s figure, (central object), the straight, loose line touching the corner of the cube looks bent. In the figure to the right, the straight line interrupted by the corner looks bent.

I don’t think we really understand any of these illusions, and since they are not very dramatic, you don’t notice them very often. There’s probably a different explanation for each. For example, both the left and middle figures show a bent line that is the backbone of two triangles meeting at a point, so you might think “Hello, we’re getting somewhere”. But then you notice that the lines bend in different directions relative to the triangles inside each illusion.

The Bourdon Illusion, Humphrey's Figure and Corner Illusion
The Bourdon Illusion, Humphrey's Figure and Corner Illusion

29 Replies to “The Bourdon Optical Illusion”

  1. Whoa, they look bent!

    That was sarcasm =D It’s not a very dramatic illusion, I agree, Vurdlak. But I understand that you can’t post explosive great illusion day in day out. So this one is okay. The middle one, Humphrey thingie, is the best one, in my opinion.

    Keep up the good work, dude!

  2. i don’t get it…the upper parts seem to be a line and the lower parts seem to be a bow or what?
    and the other ones look quite normal to me too

    maybe i’m just too stupid to really see the sense of these illusion ^^

  3. Well, I have to say that all those lines look straight to me. I don’t see any bending…

    Strange as I usually see these illusions and love them!!

  4. I can understand as to why most people would see a bent line.

    With the way the black triangle “edges” are set up, the majority of people would look at the ‘bottom’ of the triangles, not the ‘top’.

    Even I did at first.

    But! If you would clearly focus on the ‘top’ of the triangle edges, it does look like a straight line.

    Maybe I’m wrong, but it’s just my own guess. :D

  5. …this illusion is rather simple and is just the matter of the mesurements your brain makes…the two lines make up the illusion

  6. It’s been two or three days now for this illusion and there still aren’t even comments for us to read. I know there are comments because I left one two days ago.

  7. There must be something wrong with me.

    All of those lines look absolutely perfectly straight to me, from the moment I saw them.

  8. some of these are whack but some are ok and some are amazing but what do i know cuase i didnt make any

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