Fascinating article by Rhitu Chatterjee in Science this past week. I am not a specialist in physiological optics, but I have always understood that you cannot give sight to someone who is blind from birth and is older than, perhaps, a teenager. According to Chatterjee's article, most ophthalmologists understood the same thing. It is not true.
Chatterjee describes a project to perform cataract operations on people who are congenitally blind. Some of these are teenagers or young adults, and they learn to see – not as well as you and I, possibly because part of their visual cortex has been used for touch or hearing, but they learn to see. In consequence, a neuroscientist, Pawan Sinha, launched Project Prakash as a humanitarian effort to give sight to people who have blindness that would be preventable in the developed nations.
What interested me more, in a way, was that newly sighted people fell for precisely the same optical illusions that normally sighted people fall for. For example, the two bars across the railroad tracks in Figure 1, the Ponzo illusion, are the same length, as you can verify with a ruler. The dashed lines on the right side of Figure 1 are parallel and show that the two bars are the same length – except that the illusion persists, and the dashed lines do not look parallel.
Figure 1. Ponzo illusion. The "more distant" bar appears longer than the "closer" bar. The usual explanation, that we learn to see perspective in drawings, is apparently falsified by the fact that newly sighted people also fall for the Ponzo illusion.
Probably most readers are familiar with the Ponzo illusion. The usual explanation is that we learn over time to recognize 2-dimensional drawings of 3-dimensional objects, and we think that the upper bar is farther away than the lower bar and so must be longer.
Amazingly, 9 newly sighted children fell for the Ponzo illusion.
Likewise, Figure 2 shows the Müller-Lyer illusion. Here, (a) the line segment with the arrows pointing out always looks shorter than (b) that with the arrows pointing in. The illusion persists, even when we provide a ruler to show that the lines are the same length. (See also here for a slightly different view of the Müller-Lyer illusion.)
Figure 2. Müller-Lyer illusion. (a) The line segment with the arrows pointing out looks shorter than (b) the line segment with the arrows pointing in. The illusion persists even when we provide a ruler for reference. Newly sighted people also fall for the Müller-Lyer illusion. From M. Young, No Sense of Obligation, Science and Religion in an Impersonal Universe (2001).
Once again, the 9 newly sighted children fell for the illusion.
No one Chatterjee spoke to has a good explanation, but it seems that we must be hardwired to perceive and interpret much more than is commonly thought.
19 Comments
MJHowe · 24 October 2015
Is it just me or are the letter 'a' and 'b' transposed in the second image?
Joe Felsenstein · 25 October 2015
gnome de net · 25 October 2015
MJHowe said:
Is it just me or are the letter 'a' and 'b' transposed in the second image?
Relax. It's not just you.
Matt Young · 25 October 2015
Yes, thanks, I have switched "in" and "out" in the text.
Also, Joe Felsenstein submitted the following comment, which somehow disappeared from the Comments but which I received by e-mail:
Is it just me, or does the ruler really show that the left-hand line segment is 7.5cm long, while the right-hand line segment is 8cm long?
There is an uncertainty due to the thickness of the lines, but even so, the right segment is a smidge longer than the left. I imported the drawing as a jpg from a picture I drew with an antiquated program around 1999, and the conversion must have distorted it somewhat; note that the "15" is located to the left of where it should be, so it looks at first glance that the right segment ends at 15.5 cm, whereas it really ends at 15. I may redraw the figure for posterity, but not before the middle of next week.
Joe Felsenstein · 25 October 2015
It was I who disappeared my own comment, after only a minute or so. I realized that I had simply misread the ruler scale, in the way you noted.
Shebardigan · 25 October 2015
Fascinating. Neither of these illusions works for me.
I am not entirely neurotypical, however.
gnome de net · 25 October 2015
Matt,
Switching "in" and "out" is a good start, but now you need this:
(a) The line segment with the arrows pointing out looks bigger smaller than (b) the line segment with the arrows pointing in.
At least it does to me.
Matt Young · 25 October 2015
Can't read my own writing, even when it is typed. (b) looks longer than (a). I'll try to fix that.
Shebardigan · 25 October 2015
I'm having a bit of trouble discerning where the optical illusion is in Fig 2. Segment (b) both appears to be longer than (a), and actually is. My initial estimate was about 5% longer, before noticing the handy ruler.
Robert Byers · 25 October 2015
I think i have a good explanation. It only touches on origin ideas a little, yet a little. the newly sighted people will be no different because its the same mechanism for seeing. We do not see anything but rather read a memory from our senses and so the eyes. Then it is edited by fixed principals in our memory. The newly sighted people don't need to learn anything. The fact they are successfully seeing is proof of the same principals being used as everyone else. It could only be this way. Their memory organizes sight the same way as everyone. Optical illusions show that our memory edits out minor details. These illusions are not found in nature but made by men. They simply, simply, show we don't see anything but only a recording and that edited in minor ways. In all senses info this happens. On NOVA these weeks there is a brain series by David Eagleson that touches on these matters and includes the idea we make reality in our head and not from our senses seeing reality. This is wrong but shows what we see etc is not what is there. In fact its 95% reality accurate. its just a editing thing but Eagleson and others conclude we make it all up. Nope. Illusions show the truth we don't actually see anything but only WE observe a memory from the senses. In origin matters this backs up that we are immaterial souls meshed to a great memory machine. THis is the mind. We have no brain but only soul and memory/mind.
Its not why do newly sighted people see the illusions but why shouldn't they!!! They are hardwired like everyone in how senses are used by US. in the end they all should see the illusions like everyone except in special cases as a poster here said they don't see them.
Shebardigan · 25 October 2015
And it dawns on me why Fig 1. did not work: I saw it as a trellis rather than a railroad track.
Yardbird · 25 October 2015
Robert Byers said:
We have no brain...
Certainly seems like that for some of us. (Sorry. It's hard to lay off the softballs. Done now.)
gnome de net · 26 October 2015
The optical illusion is exaggerated by the thickness and locations of the arrows. Line "a" is 7.5 cm including the arrows; line "b" is 7.5 cm excluding the arrows. Line "a" between the thick arrows is less than line "b".
j. biggs · 26 October 2015
Shebardigan said:
And it dawns on me why Fig 1. did not work: I saw it as a trellis rather than a railroad track.
For me the second image (in fig. 1.) clarified things and made me see the image as three rather than two dimensional. So now I see two intersecting planes that are perpendicular to each other.
DS · 26 October 2015
Well in figure two the two line segments are exactly the same length, at least on my screen. But the first segment definitely appears shorter and the problem isn't just the arrows. According to the scale, the left segment is 7.5 cm and the right segment is 8.0 cm. So the scale is wrong and is part of the illusion. The illusion does not persist despite the scale, it persists at least in part because of it.
gnome de net · 26 October 2015
Look closely and you'll notice the numbers on the scale gradually shift to the left. 15 on the scale is below the hash mark for 14.5 cm.
Shebardigan · 26 October 2015
Correcting for my sloppy measurement methods, I concur that they are of equal length.
Dr GS Hurd · 27 October 2015
I love these perceptual illusions.
They are why we use scientific metrics like ruler
ashleyhr · 28 October 2015
On the 'Conjunction' post, there's Venus, Mars and Jupiter 'close' together as viewed from Earth on 29 October. And on 7 November the moon close to both Venus and Mars in the sky.
19 Comments
MJHowe · 24 October 2015
Is it just me or are the letter 'a' and 'b' transposed in the second image?
Joe Felsenstein · 25 October 2015
gnome de net · 25 October 2015
Matt Young · 25 October 2015
Joe Felsenstein · 25 October 2015
It was I who disappeared my own comment, after only a minute or so. I realized that I had simply misread the ruler scale, in the way you noted.
Shebardigan · 25 October 2015
Fascinating. Neither of these illusions works for me.
I am not entirely neurotypical, however.
gnome de net · 25 October 2015
Matt Young · 25 October 2015
Can't read my own writing, even when it is typed. (b) looks longer than (a). I'll try to fix that.
Shebardigan · 25 October 2015
I'm having a bit of trouble discerning where the optical illusion is in Fig 2. Segment (b) both appears to be longer than (a), and actually is. My initial estimate was about 5% longer, before noticing the handy ruler.
Robert Byers · 25 October 2015
I think i have a good explanation. It only touches on origin ideas a little, yet a little.
the newly sighted people will be no different because its the same mechanism for seeing.
We do not see anything but rather read a memory from our senses and so the eyes. Then it is edited by fixed principals in our memory. The newly sighted people don't need to learn anything. The fact they are successfully seeing is proof of the same principals being used as everyone else. It could only be this way. Their memory organizes sight the same way as everyone.
Optical illusions show that our memory edits out minor details. These illusions are not found in nature but made by men.
They simply, simply, show we don't see anything but only a recording and that edited in minor ways.
In all senses info this happens.
On NOVA these weeks there is a brain series by David Eagleson that touches on these matters and includes the idea we make reality in our head and not from our senses seeing reality. This is wrong but shows what we see etc is not what is there.
In fact its 95% reality accurate. its just a editing thing but Eagleson and others conclude we make it all up. Nope.
Illusions show the truth we don't actually see anything but only WE observe a memory from the senses.
In origin matters this backs up that we are immaterial souls meshed to a great memory machine. THis is the mind. We have no brain but only soul and memory/mind.
Its not why do newly sighted people see the illusions but why shouldn't they!!!
They are hardwired like everyone in how senses are used by US.
in the end they all should see the illusions like everyone except in special cases as a poster here said they don't see them.
Shebardigan · 25 October 2015
And it dawns on me why Fig 1. did not work: I saw it as a trellis rather than a railroad track.
Yardbird · 25 October 2015
gnome de net · 26 October 2015
The optical illusion is exaggerated by the thickness and locations of the arrows. Line "a" is 7.5 cm including the arrows; line "b" is 7.5 cm excluding the arrows. Line "a" between the thick arrows is less than line "b".
j. biggs · 26 October 2015
DS · 26 October 2015
Well in figure two the two line segments are exactly the same length, at least on my screen. But the first segment definitely appears shorter and the problem isn't just the arrows. According to the scale, the left segment is 7.5 cm and the right segment is 8.0 cm. So the scale is wrong and is part of the illusion. The illusion does not persist despite the scale, it persists at least in part because of it.
gnome de net · 26 October 2015
Look closely and you'll notice the numbers on the scale gradually shift to the left. 15 on the scale is below the hash mark for 14.5 cm.
Shebardigan · 26 October 2015
Correcting for my sloppy measurement methods, I concur that they are of equal length.
Dr GS Hurd · 27 October 2015
I love these perceptual illusions.
They are why we use scientific metrics like ruler
ashleyhr · 28 October 2015
On the 'Conjunction' post, there's Venus, Mars and Jupiter 'close' together as viewed from Earth on 29 October. And on 7 November the moon close to both Venus and Mars in the sky.