The train track optical illusion that's bewildering the internet

[Andrew of Ware]

Not sure if this is the right forum, but I suspect the answer is something scientific.

This video - of a father shuffling around his son's toy train tracks - has bewildered the internet. Can you figure out what's causing the optical illusion?

http://www.bbc.co.uk/news/blogs-trending-35989211

[Em]

Originally Posted by Andrew of Ware

.. I suspect the answer is something scientific.

The answer is in the article you linked.

[ganzfeld]

Its name is in the article but the reason for the illusion is not known (which is true for most optical illusions).

[Andrew of Ware]

Ah. I read the page in bed this morning before getting up. The BBC updated the page when I wasn't looking.

However, is there also something about the camera angle? Looking at the still of the start of the video, the top arc of the upper piece of track does seem shorter than the top arc of the lower piece.

[ASL]

Originally Posted by Andrew of Ware

Ah. I read the page in bed this morning before getting up. The BBC updated the page when I wasn't looking.

However, is there also something about the camera angle? Looking at the still of the start of the video, the top arc of the upper piece of track does seem shorter than the top arc of the lower piece.

Looking at it cross-eyed, (so one image is imposed on the other) it does look like the one on top is a very little bit shorter than the one on bottom, but only just a bit. Could easily be due to the perspective of the one on bottom being a little closer to the camera.

[A Turtle Named Mack]

It would have been a nice addition to the video to take the piece which had been at the bottom and put it to the opposite side of the other, so one could see that it then looks like the smaller piece.

[overyonder]

There's nothing wild there. He's aligning the TOP of the bottom section of track with the BOTTOM of the top section of track. The angle of the camera makes it even "worse".

If you used cartesian paper, it would be much more evident.

OY

[musicgeek]

I used to have a licensed Harry Blackstone Jr. Magic set that included a pair of cardboard rainbows with which to mystify audiences with this illusion.

[Mochrie99]

I remember seeing that illusion when I was a kid when I saw a tv program out of Detroit called "Kid Bits" and the host demonstrated it using curves cut from paper plates. It's a really weird effect, but pretty cool. He also demonstrated other famous optical illusions from what I remember.

[ganzfeld]

Originally Posted by overyonder

If you used cartesian paper, it would be much more evident.

Is that really so? Did you try that?

I suppose you could say there's nothing wild and it just that the top is aligned with the bottom but here we are over a hundred years after its discovery (or rediscovery at least) and no one can say definitively why it happens so I think that's pretty wild. If we consider the model that people simply compare the size of the nearest side then other 'correct' comparisons and illusions would would not occur. Yet they do. So your explanation is missing something.

[overyonder]

Originally Posted by ganzfeld

Is that really so? Did you try that?

With my lousy photoshop skills:








OY

[UEL]

Originally Posted by overyonder

With my lousy photoshop skills:

OY

See, you needed photoshop to do it...

[ganzfeld]

Originally Posted by overyonder

With my lousy photoshop skills:

Cool! IMHO, the illusion persists in the second image despite the grid. But one opinion isn't that meaningful.

[A Turtle Named Mack]

That's one of the cool things about this illusion, Ganz - it persists even when you know the trick. I was fully aware of the situation when first viewing the video, but my rain's non-conscious processing centers still told me the top on was much smaller. The grid allows you to compare the lengths numerically, but visually your brain still says the top one is smaller.

[thorny locust]

Interesting. I see the illusion clearly without the grid; but, with the grid, the two look the same size to me; or at any rate much closer to it.

[overyonder]

Originally Posted by thorny locust

Interesting. I see the illusion clearly without the grid; but, with the grid, the two look the same size to me; or at any rate much closer to it.

Yes, and they are. It's the same pic that's pasted twice (at the same size). The point I was trying to make is that in the video, the track piece are aligned on a slanted plan (bottom pic on my post), not on a vertical plan (top pic on my post).

The angle of the camera adds to the visual effect.

OY

[thorny locust]

Originally Posted by overyonder

Yes, and they are.

Yes, I understand that. The question isn't whether the two are actually the same size, but whether the presence of the grid causes the illusion not to be perceived; and if so whether it does so for all people -- apparently it does for me but not for ganzfeld.