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What the Leaning Tower and related illusions reveal about how your brain reconstructs 3-D images.
July 8, 2008 | 13
In the Leaning Tower Illusion, discovered by Frederick Kingdom, Ali Yoonessi, and Elena Gheorghiu of McGill University, two identical side-by-side images of the same tilted and receding object appear to be leaning at two different angles....[More]
The Leaning Tower Illusion elucidates the way in which the visual system uses perspective to help reconstruct 3-D objects . We say "reconstruct" because the visual system has no direct access to three-dimensional information about the world....[More]
Further analysis of similar images reveals subtleties in the way our visual system processes the perception of depth and perspective. For instance, the Leaning Tower Illusion also works with paired images of train tracks, violating the rules of perspective....[More]
However, the illusion does not occur when viewing two leaning Japanese manga girls, even though the two cartoon images are tilted. The reason is that the cartoon girls do not appear to recede in depth, so our brain does not expect that they would converge into the distance....[More]
The leaning tower illusion is such a fundamental feature of our visual system that it works even if one draws a 3-D solid object as it recedes into the distance. The parallel lines give the illusion of diverging in the distance....[More]
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13 Comments
Add CommentThis is not and illusion - it's obvious. The two pictures are identical... If you actually had 2 parrellel cylinders in front of you in separate locations, due to perspective, the 2d projections of the two cylinders would result in 2 different images! If the images are identical but in different locations, they cannot be parrellel, so it's obvious that the brain would see things that way. Again, this is not an illusion - it's just due to perspective.
Reply | Report Abuse | Link to thisJust, want to add - one misunderstanding here is that people forget that eyes (and thus the brain) see the world in angular coordinates - not height and width in pixels. The two 'identical' images when transformed to projected angular images are not really identical.
Reply | Report Abuse | Link to thisJust re-reading the article again - this part really gets me:
Reply | Report Abuse | Link to this"This incredible effect was first noticed just last year".
This 'illusion' is a simple result of basic trignometric principles that have been well understood for hundreds of years, how it can be considered a new discovery I have no idea.
kieryn, I think you're missing the point. This doesn't have to do with perspective. In the visual illusion slide show the side-by-side pizza tower and railway pictures are the exact same. Yet the towers appear to be leaning in different directions (one on the right more to the right) and the railway rails appear very different (one on the right appears to run further into the distance, as I see it).
Reply | Report Abuse | Link to thisThis is an illusion, the images are the exact same, yet they appear different.
This is a simpler way of looking at it, but not entirely accurate as thinking about the angular projection - think about simple perspective drawing principles... when parallel lines get further away, the 2d projection of them converges to a point. The vertical lines in the picture of the tower are all getting further away and therefore they all converge to a point. However, If you copy the picture and put it next to the first, the vertical lines in the second picture do not converge to the same point, therefore they cannot be parallel with the first tower - hence it IS leaning in a different direction. If it was leaning in the same direction it would have to be a different image, where the vertical lines converged with the vertical lines from the first picture.
Reply | Report Abuse | Link to thisAgain, this principle has been understood in art for hundreds of years.
Kieryn and danshil, I think I can reconcile what you both are saying like this: If you look at the two pictures independently you would perceive and describe the towers as leaning the same way -- obviously, since they are identical. BUT when you look at them side by side, your brain tries to make sense of them as a single scene, which is how we usually expect to engage the world. Considered that way, Kieryn's explanation makes sense: since the parallel lines don't converge to a common vanishing point, the brain interprets the towers as leaning differently, which they would have to be *if they were part of a single coherent scene*. I suspect that this disconnect is what creates the illusion. What scientists are claiming is newly discovered is not the well-understood perspective principle, but the powerful exploitation of it to provoke this gap between perception (different leans) and reality (identical leans) when two pictures are viewed side by side: we see something we "know" isn't true.
Reply | Report Abuse | Link to thisI find it interesting that they feel it is a function of the way our minds process clues for depth perception. If I cover my dominate eye, I still see the illusion. However, covering my other eye & and viewing the images with just my dominate eye; the illusions disappear.
Reply | Report Abuse | Link to thisActually that isn't really new, we often noticed that effect as Scientific Photography students at RMIT back in the 1980's.
Reply | Report Abuse | Link to thisI find that if I close one eye and look at each picture individually I still perceive the angle as different between the two pictures. I can make the angle appear the same by moving my head sideways. This agrees with others who have said that the image is not really the "same" for each eye. I wonder if this is more related to the same effect as looking at a photograph of a person. As you move about, the eyes seem to follow you even to extreme angles. We are interpreting the flat photograph as a 3-d object. The angle you have to the photograph will change the perceived angles in the photograph. Obviously two side by side photos will have different angles. It is not that they are side by side that causes the illusion, it is that they are at different angles on our retina. The side-by-sideness makes this difference more obvious.
Reply | Report Abuse | Link to thisEye Illusions are awesome!
Reply | Report Abuse | Link to thisI have read this article with interest but have found the discussion taking place in these comments perhaps even more interesting!
Reply | Report Abuse | Link to thisThis discussion is itself evidence of the way our brains interpret incoming signals; it is evident/apparent that different people 'see' differently and/or interpret the data differently and/or explain it differently.
'Perception' is therefore a subjective and personal experience.
Demonstration of this is what is intended by those who draw such parallels (sic); which provoke subsequent discussion. Regardless of one's personal interpretations, this discussion validates the whole article along with its visual contributors. -It proves that we can never 'know' that our experiences are common to anyone else.
It is perhaps disconcerting that we may be wrong to believe either axiom: truth or illusion - for there can be no proof of ultimate truth and no ultimate reality.
We are all alone with our unique interpretation of what we think we think our experiences are telling us, yet living in the forlorn hope that we will find utopia through proof that we are right, by finding agreement through common consent; and for confirmation of this by comparison alone.
All we find is that there is no means of escape from our own personal singularity. We are destined to be alone for each of our unique eternities, just as converging parellels will never come together unless invoked through theoretical extrapolation.
All I find is that there is no means of escaping my own personal singularity. I am destined to be alone for all of my unique eternity, just as converging parellels will never come together unless invoked through my theoretical extrapolation.
We search for comfort but only find it when we invent it.
I have read this article with interest but have found the discussion taking place in these comments perhaps even more interesting!
Reply | Report Abuse | Link to thisThis discussion is itself evidence of the way our brains interpret incoming signals; it is evident/apparent that different people 'see' differently and/or interpret the data differently and/or explain it differently.
'Perception' is therefore a subjective and personal experience.
Demonstration of this is what is intended by those who draw such parallels (sic); which provoke subsequent discussion. Regardless of one's personal interpretations, this discussion validates the whole article along with its visual contributors. -It proves that we can never 'know' that our experiences are common to anyone else.
It is perhaps disconcerting that we may be wrong to believe either axiom: truth or illusion - for there can be no proof of ultimate truth and no ultimate reality.
We are all alone with our unique interpretation of what we think we think our experiences are telling us, yet living in the forlorn hope that we will find utopia through proof that we are right, by finding agreement through common consent; and for confirmation of this by comparison alone.
All we find is that there is no means of escape from our own personal singularity. We are destined to be alone for each of our unique eternities, just as converging parellels will never come together unless invoked through theoretical extrapolation.
All I find is that there is no means of escaping my own personal singularity. I am destined to be alone for all of my unique eternity, just as converging parellels will never come together unless invoked through my theoretical extrapolation.
We search for comfort but only find it when we invent it.
I do not quite understand the following statement: "Thus, two truly parallel towers, such as the Petronas Twin Towers in Kuala Lumpur, appear to converge in the distance as they recede. "
Reply | Report Abuse | Link to thisThe towers, as viewed in this picture, do not appear to be converging at all. To my eye, the distance between the towers at the top is identical to that at the bottom.