Wisconsin Public Television University Place Presents  Christopher Tyler Depth Perception from DaVinci to the Present  September 21, 2012 UP771  cc >> Welcome to University Place Presents. I'm Norman Gilliland. How did they do it? For centuries, a challenge for painters was to create a three-dimensional image in a two-dimensional medium, such as a canvas. Then about 500 years ago during the Renaissance, painters seemed to get suddenly, rather suddenly at least, very sophisticated at representing three dimensions in that two-dimensional space. Were they using optical aids such as lenses to help them out, or perhaps some mathematical schemes? Or was it just a matter of a lot of practice and eyeballing? Well, my guest has done considerable research into the area of space representation in painting, and he has come to Wisconsin via the McPherson Institute of Eye Research, and as a way to bridge some of the gap between art and science. He is Christopher Tyler. He is a visual neuroscientist, and he's also the head of the Smith-Kettlewell Brain Imaging Center in San Francisco. Welcome to University Place Presents. >> Good to be here. >> How did you get interested in this topic in the first place? >> Well, I spent my career doing the science of depth perception, stereoscopic vision, how the two eyes combine to give you a sense of three-dimensional space, and I started to want to expand in studying the history of this and look at how has it been done through the ages. 

>> What would be, then, sort of the logic, if you will, of space perception? >> Well, the key is perspective, and the logic of perspective is that you're viewing an object through a frame which represents the canvas or the picture, and the light rays projecting through that frame tell you where every point should be from that particular viewpoint. So the perspective is correct if seen from that same viewpoint that it was constructed originally. >> So I think we have some building blocks here represented in this area of perception of space in a dimensional space. What's this first image representing? >> Well, this is a painting from the 18th century representing the geometry of what I just described. Here's a viewer looking through a plane at a cube. So the world that's being represented is this cube, and those lines show exactly where the places where those lines intersect the plane is where the painter should be painting. And it gives you a strong three-dimensional impression. >> And then we also get into some other aspects over here which seem to be representing, are we at vanishing point yet? >> Yeah. So, this shows when you follow this geometry, objects such as cubes have lines that project a single vanishing point, and this is a key issue of understanding the geometry. They don't just converge, but they converge all to the same vanishing point. 

So, this next image is showing how students draw cubes. They were asked to draw a physical cube on a piece of paper, and the dashed lines here show the shape that they should have followed, and the drawing shows exactly what the students did. And they don't even come close. >> Yeah, how do we account for that? >> Well, it's a difficult reconstruction problem to understand how the world should, in fact, be represented on paper, and even here in the 21st century, my students are not getting it right. >> And we get into a little bit of the neurology of it here. >> This is getting a bit detailed, but it shows how when the two eyes are viewing a scene, the image projects back through the visual pathways to the back of their head. And I'm talking here about the compression effect. So the circular image here shows the world and it's projected with a compression which is called magnification function to the cortex. This has to be taken into account if you really want to understand visual processing. >> At what point do we see the image, which logically, physiologically, would be upside down, at what point do we see it reversed? >> Well, this is a philosophical issue, the infinite regression of the homunculus at each part of the brain it's looking at the previous part. 

And so, exactly how the whole thing gets put together into our perception remains, still, a philosophical conundrum. >> What do we have here? >> Well, this is a replication of the same image below, but it shows for a cartoon that will come up next. Bart Simpson, this is how he would predict, this is the conundrum that the rest of the brain has to solve in order to understand what it is actually looking at in the outside world. >> And then this whole question of stereoscopic vision, how far back does that go? >> Well, stereoscopic vision was discovered in about 1830, but that's not what is showing up on the screen. >> Are these images identical or are they shifted just a little bit from one to the other? >> Actually, no. This is a depiction that is perhaps best shown in the next slide. So, the image on the left is a perspective scene, a scene of the real world, and on the right is shown the degree of information which is public transferred into the peripheral vision of the human observer which is much, much reduced, much distorted. And the point I'm making here is that they're still, nevertheless, good perspective information despite the degradation of the visual processing. >> Not to mention, of course, the degradation that one individual's vision would experience over another's. >> Oh, yes. 

>> No two people see exactly the same, do they? >> Right. And particularly when they have any kind of visual problem. >> Sure. Maybe we'll touch on that a little later as we get into some of these paintings too. It is a fascinating topic. This represents, then, getting back to this one? >> Here I'm starting to show an inverse history of perspective. So, starting in the 20th century, this is a computer graphics image really using perspective to get a strong, vivid sense of depth. >> And this one I find particularly intriguing too. >> This is from the photo-realist movement. He's, again, using reflections and a strong perspective to express a vivid sense of depth going back towards the '50s or '60s. 

When is this? >> This would be... >> '70s, sorry. >> Yes, 1974. Well, one painter who is notorious for bending, distorting perception and perspective is Salvador Dali. >> Yeah. >> Well, what is he doing exactly that so effective? >> He's a surrealist but in a sense he's a strong realist. He uses very realistic detailed depictions in order to carry the sense of surrealism by then adding some weird distortion. Here he's using a distortional perspective so that the scene is rotating as it goes vertical from the landscape below to the cross above. >> And another artist that you have pointed out is doing some rather interesting things is Kandinsky. >> Well, here, Kandinsky is using all the elements of perspective, but deconstructing it to say these are the pieces we use. 

>> He's scattering them around? >> He's scattering, exactly. >> So we would have, how many would we have? How many vanishing points would we have in a painting like this? Any number? >> I think he's given up entirely on that. [LAUGHTER] >> Well, now we're getting into some, what we might call, classic paintings here. This one is demonstrating the image falling off, certainly. >> What's interesting here is it's a two-point perspective construction by Canaletto. And this was widely used in the 18th century. >> And for what? To demonstrate how to do a two-point perspective? And how does that work? >> It's just an elaboration, the variety of images that you can depict in three dimensions with perspective. >> Did I understand correctly that he used a device to create this effect? >> Well, it's well known that Canaletto had a camera obscura, which is a device for projecting images before the invention of the camera as we know it. It's not clear how much he used the camera obscura in his actual paintings. >> So that continues to be a little bit dicey, doesn't it? We know, for example, people had lenses, but what did they use them for exactly? >> Exactly. 

It's a continuing debate. And in the 15th century there was proliferation, a very strong perspective. This is one-point perspective exemplified by Crivelli. >> So this is where we start to touch on a bit of mystery, don't we? Why suddenly this emphasis on a stronger perspective in the 15th century. What's happening? >> Well, if you want to get into the debate, the problem with the optical projection concept is that it was only available for small local regions. So you'd have to move the lens from one place to another and then you'd have breaks. Each one would be an accurate perspective, but they wouldn't match each other. Whereas here, Crivelli, everything goes to a single vanishing point. So, to me, that argues against the idea of using optical projection. Besides which, you have to have the actual scene in order to project. 

But this is a fantasy scene. >> That's an interesting point, isn't it? We've been talking and probably will talk mostly about western Europe, but what were the Chinese, for example, doing at this point? >> I was particularly interested to realize how accurate or how rich these Chinese body of art was as early as the 10th century or the 11th century. But the Chinese almost universally used parallel perspective rather than converging perspective. Here they're kind of doing a compromise between parallel and convergence by having parallel regions but having them in two different directions as though they're converging. >> What are they trying to accomplish with that? >> It's difficult to interpret, but you have to remember that a lot of Chinese paintings were painted on scrolls would could be as much as 50 feet long. >> True, yes. >> So that seems to be a strong constraint against having central convergence from everywhere in the scroll. [LAUGHTER] >> That could be a little tough to pull that one off. And we also get some very interesting effects when we look at other nationalities too. Egyptian art comes to mind, for example. 

But I gather, they're after something different in most Egyptian art. They're not after a realistic sense of depth when they have the relative sizes of objects. >> It seems much more like a cartoon strip depicting a story as it goes along different places in the strip rather than attempting to depict depth. >> And the relative size of figures would represent the relative importance in Egyptian art? >> Right. They size more to depict importance, and actually not at all to depict distance. >> And here being another example of that. Clearly not too great an effort to create three dimensions. >> Well, I put this in because, actually, the rays of the sun are convergent. And the rays of the sun are convergent because of perspective. >> Okay, so it's kind of a mix? >> Yes. 

So this is one particular symbolism that is the only way that the Egyptians incorporated perspective in their work. >> Now, the Egyptians did a lot of work with stone of course. Did they use that stone to create depth? >> Well, this is an example showing how they used interposition or overlay to depict depth. There's no diminution. So there's no convergence, but they're showing object in front and other objects by just putting them... >> Physically farther back. >> Superimposed. >> Now, what about some of my favorite paintings, the ones that we find in the caves? It's some fantastic works of art, regardless of what's going on with space perception. >> Yeah, it's just extraordinary to follow back and to see how long ago these paintings were painted. 30,000 years ago. 

Not 3,000. 30,000 years ago. And they use a lot of realistic depictions. Shading and accurate forms and so on, and yet, they just seem to draw the objects haphazardly on top of each other as they don't really care about the arrangement. This is puzzling. >> Are they using, in these cave paintings, are they using at all the texture of that cave wall to create effects? >> That has been used. It's not really a typical trend. What was particularly interesting about this painting is that it's the only example I could find that was actually used as what you might think was perspective. The top here is shown a rank of long-horned rhinoceros, and the horns are actually decreasing in size by a factor of three which I'm interpreting as being from front to back, and that's he first example in history as the use of perspective. >> Just a little hard to know exactly who was doing what since we have multiple artists superimposed over how many thousands of years. 

>> Right, right. >> But, certainly, a style that was developed, a very distinct style in those cave paintings from 25,000 years ago or so. What about Roman art? Do we find much use of perspective in that? >> Yes, it's actually written about in some detail by Roman writers such as Vitruvius 2,000 years ago, and the painters also knew this and used it as a technique. So this is one example where if we reconstruct from local regions of the steps and other parts, they all seem to have angles that converge to a single vanishing point. >> And we're seeing this here, I think. >> Yeah. The red lines. >> As we watch. And so, again, vanishing point is that point at which the perspective kind of disappears into the background. >> Right. 

But if it's accurate, then, at least for one style of perspective, they all have to converge to one single point. >> One place that I would think that would be necessary, particularly necessary to have three dimensions would be if you're doing a schematic or a drawing or what might be called a model of a building. >> Well, this is another point from Vitruvius that he clearly specifies the concept of a planned elevation and perspective and in those explicit words. Although artists don't often attribute perspective, as you said in your introduction, as being developed in the 15th century, but the word perspective is used in the architectural context by Vitruvius who planned looking down on where the building could be. The elevation being the front of the building, and the perspective being the three-dimensional view of this realistic sense of depth. >> Which requires quite the different, it's almost a different skill entirely from the other things we've been seeing. Now, if we go back to China for a while and look some more at this, you're calling it parallel perspective? >> Well, here I want to turn to the perceptual aspects. So the parallel perspective is a formalism that allows you to depict some sense of depth, but you also get a bizarre sense of expansion into the distance. The far regions look larger than the near. >> So what do you attribute that to? That can't be just a matter of it being a scroll? >> The lines here are showing that they really are parallel. 

>> They really are. >> Even though they seem to diverge. >> It's an illusion. >> It's an illusion. It's a depth illusion. >> Do we know what they were trying to accomplish with that? >> As I said, I think the parallelism is a required formalism in order to get a lot of information onto scrolls, and then you get a resulting illusion that they're struggling to avoid. >> And this shows us a little bit in what's going on here. >> Well that effect in China reminded me of this illusion from Roger Shepard where these tabletops not only have this parallel divergence effect, let's go back, but remarkably, the two tabletops are exactly the same shape on the paper. >> I really have trouble with that. [LAUGHTER] >> That's why it's a real illusion. 

>> I even took out a ruler and tried to measure them, but somehow I didn't get very far. But yes, it is a fascinating illusion. And so how is that illusion built exactly? >> Well, I believe it's a perspective illusion because the orientation of the two parallelograms is such that one appears to be receding in depth. >> True. >> And the other one doesn't so much. >> And we'll see some of that same thing applied. >> Here I was just showing that it's reminiscent of the two tables in this Chinese... >> Absolutely. Yes, absolutely. They're doing the same kind of device, and I think we'll see the principle behind that one also in a second here, coming in and illustrating how the parallels work. 

>> Exactly. So most of these lines are all parallel to each other, but some are locally parallel. but divergent from the others. Why don't they all go together and start probing the mystery? >> Right. Yes. Definitely. Do we see much interaction in this matter between east and west in 15th, 16th century even? >> I don't think so. There are almost no examples of convergent perspective in Chinese art, even coming up to the 19th century. >> Really? Up to the 19th? >> Yeah. >> Largely because religious use is for a different purpose, different medium, really? >> Yes. I think it's probably driven largely by the medium. 

>> Now, here's a familiar face. The fascinating thing about da Vinci, that he started so late. >> Yeah. Most of his work is from his later years, and yet, this is atypical of major artists. They normally do an apprenticeship and come out with great stuff in their formative years, their 20s, and there's so little work known from da Vinci in his 20s. There's one in Washington, DC, an early da Vinci. It's about the only finished work that is available from him in his entire, up until age 30. >> So what do you suppose was going on in those first years? >> So, this makes an interesting problem to look into in terms of art historical analysis. I spent a lot of time probing, a lot Internet searches, and so on, to see what he might have been doing in that period. And one key factor is that he was working with geometric analysis of perspective, and that's shown in the next slide. 

This is a diagram from those same years showing Leonardo's depiction of how you draw perspective. What's interesting here is that he's drawing a globe. >> Which is, it seems to me, a singular challenge itself to represent in two dimensions. A sphere, it just seems to me, would be the hardest thing to represent. >> Well, not necessarily because it projects as a circle, and that's a very bleak angle. But what's interesting is that he's focused on this structure, which represents the spherical universe with the spherical Earth. This was all, of course, before Columbus discovered America, before the world was really understood to be spherical. >> Yeah, so he's certainly current in his science there. And in a minute we'll get to a fascinating representation of that sphere, the globe in fact. Is this one of the devices that would have been used for creating this effect? >> This is just a reconstruction of what was shown in the previous drawing. 

The main focus of this talk is to look at the relationship between Leonardo and other great thinkers in perspective in that same period when he was in his 20s. So, two older figures from Renaissance Florence were Uccello and Toscanelli. Uccello was a well known artist who was often attributed as being fascinated by perspective. And Toscanelli was a mathematician who had worked with the supposed originator of perspective, Brunelleschi. So the mathematician and the architect were supposed to be two of the first. >> We know that they were connected? >> Yeah. >> That they interact? >> Yeah, they had extensive interactions in those early days. Neither of them had normally associated with Leonardo da Vinci. So, what I'm doing here is pulling out connections that suggest that there were associations. So here, Uccello's famous for this polyhedra and on the right, and da Vinci has drawings of the very same objects. 

>> That does give you a smoking gun. [LAUGHTER] What about artists, if we pick any particular artist, do we see inconsistency in their representation of perspective? >> Well this is the remarkable thing about Uccello, although he has the reputation of being very interested in perspective, his own paintings are not necessarily an accurate perspective. And his most famous painting is the Saint George and the Dragon which doesn't have a whole lot of perspective, but it does have these flower beds that allow us to analyze the perspective convergence. All the receding lines at the edges of those flower beds should converge to a single vanishing point. So they don't converge to a single vanishing point. Whereas Leonardo da Vinci is very clear about the accurate convergence as shown by his own diagram here in preparation for Adoration of the Magi. >> We do have a sense that this one with the faulty perspective was an early one. >> It was pretty much in the same era. Uccello was, again, a friend of Brunelleschi and Donatello. He should have known the rules of perspective by then. 

So it's very strange that he would make those mistakes. So, now I pursue this story by looking at another painting of Uccello's which is very hard to interpret. It looks like a big mess. >> It is. It's pretty muddy, yes. >> Yeah. But what's interesting is when they took this off the wall, they found an underdrawing or sinopia, which is shown in the next slide, which is an extremely accurate perspective. So I'm trying to counterpoint. We see the inaccuracy of Uccello's perspective with the fact that Leonardo was around at that very same time, and he understood the accurate, logical perspective. >> Yes. 

>> It's a wild hypothesis in terms of art history, but I'm hypothesizing that maybe Leonardo, in his wanderings around Florence, was actually working with Uccello. >> On perspective. >> Yes. And perhaps did this underdrawing himself. As I said, it's a wild hypothesis. >> I'm sure some analysis of this image will indicate whether it's likely to be by Leonardo. >> Well, there's not much to go on in terms of artistic style. But just the fact that it's an extremely accurate perspective, which Leonardo did, as opposed to the inaccurate capabilities of Uccello, I think is rather telling. So, now this is another painting by Uccello which, again, looks like a different style from the well known George and the Dragon, Saint George and the Dragon. >> Yes. 

>> So I'm wondering, again, did Uccello really paint all of this, or could Leonardo have been involved in the painting as well? >> I think we have detail here. >> I'm particularly drawn to this figure of Noah who looks like a very noble patrician character. >> Yes. >> And I would say uncharacteristic of Uccello's own portraiture. >> And so, what's going on? >> So perhaps Leonardo painted it, and then I started wonder, well, who does it look, if it was painted from life, who could it have been representing? So I came across these other images of this mathematician Toscanelli, and I see some resemblance in the turban and there's something strange about the mouth in these drawings. So, again, a wild hypothesis, but I'm proposing that there's some kind of evidence that Leonardo may have known Toscanelli, the mathematician, that reflected Leonardo's own strong mathematical interests. >> Well, we're always coming across these fascinating possibilities of who is that in that painting really? >> Yeah. >> Contemporary of the painters but perhaps the painter himself in some instances. So we know that they did that kind of thing all the time in Leonardo's day. >> So how could Leonardo have known Toscanelli, but it turns out that in the year 1468 when Leonardo was 16, Toscanelli made a big public demonstration of boring a hole in the roof of the -- which had been recently completed, in order to allow the sun's rays to come in and project to a structure on the floor called a gnomon which indicated the seasons and the progression of the sun. 

>> A very old idea. >> Yeah. And the reason the church was interested in allowing this is because they wanted to define when Easter would be every year. >> Well, that makes sense. A good, practical reason. >> Otherwise you think, why would they bore holes in the roof of a cathedral? So he not only did this, but he made a big public demonstration. Everybody in Florence was invited, and Leonardo himself had worked on the roof the cathedral. That you can't really see, but at the top of that, the pinnacle of the -- is a golden ball. And this golden ball weights two tons, and it was put up there that very same year by Leonardo's master, Verrocchio, with the help of his apprentices, which would have definitely included Leonardo. >> Well, another example, I would think, you actually sort of alluded to this earlier, another example of perspective would be in maps. 

>> Exactly, and you can imagine if Leonardo is viewing Florence from the top of a cathedral, he would naturally get a view of the city and be interested in mapping. You can see how it could lead to an interest in mapping. >> And a point of view in mapping, for example. Now, this is an interesting one, and it's a circular map. >> It's a circular map, and it's drawing a relationship between this circular visual field. It's, again, very hypothetical, but it shows the kind of detailed maps that Leonardo is really one of the first people to draw. >> Speaking of drawing, here is some more from Leonardo. >> And so, he drew endless landscapes and bird's eye views of the environment, not only around but other regions of Italy. >> For example? >> So, here I'm saying however, although he has a reputation for being the first painter to paint landscapes, this was not, in fact, the case. This is not by Leonardo. 

This is by a relatively unknown painter called Masolino da Panicale who does all kinds of amazing things. >> It's actually a panorama, isn't it? >> It's a panorama, and it's a fantasy panorama. And if you zoom in on it, you see that he has some very bizarre buildings. It's hard to imagine anyone even conceptualizing in the 15th century. And this was 40 years before Leonardo was born. >> Now here is an example. We've been talking about vanishing points, and this one really seems to be a very obvious conspicuous example of vanishing point. >> Yes, and, again, this is by Masolino and it's many years before Leonardo or anyone else really was doing accurate perspective. It's an obscure chapel north of Milan that I actually visited. And I knew this painting, and I said to the person showing us around the chapel, you know, I know where the vanishing point should be on this painting, and we went over and looked at it and there's a hole in the plaster. 

[LAUGHTER] I predicted. Now, the hole in the plaster is a remnant of how they would have constructed the perspective. They put a nail in the wall and stretch a string out in different directions. >> Yes. >> And use that to define the direction of the accurate perspective. >> So not really a mathematical approach so much as just a visual one. >> Yes. >> And that vanishing point seemed almost exaggerated to me. It must be almost unrealistic in the way he represented it. >> And this is what the art historians say. 

They don't like Masolino's paintings because there's too much perspective. But I'm interested in historical viewpoint. This is very early, and so Masolino was one of the originators. >> And here we're back to speculation about contemporaries of Leonardo's. >> Yeah, so now I want to look at Toscanelli was a cartographer, and he is reputed to have drawn the map Columbus used to discover America, or to try to discover the Indies which ended up discovering America. Toscanelli was intimately associated with that process, and this is a reconstruction of the map he is supposed to have used. You notice it goes straight from Africa from Japan. >> Yes, a little optimistic there. [LAUGHTER] Columbus was supposed to have taken, what was it, the smallest estimate of the size of globe and superimpose on it the largest estimate of the land mass and said, oh, look it's just a hop and a skip and a jump over there. >> I didn't know that. 

>> He was a bit of a salesman apparently, as one would have to be to raise the money. >> So, soon after, so that was 1492. So here in 1507, this is a famous map showing what was known at that time. A little skinny strip that is America. What is very curious to me is how he tries to finish the edge of the Earth. He even has Africa sticking out over the edge. He really, philosophically, doesn't know what to do with the edge of the Earth. >> Right. >> He's throwing up his hands. >> It could be a bit of a challenge. 

But this is the one that really fascinates me. >> Then I came across this amazing map. It was found among Leonardo's papers at Windsor. It was presumably Leonardo's map but is a complete globe. >> Right. Again, it's representing three dimensions in two. >> Exactly. >> By splitting it up which was a technique that was used for many years. It still is to some extent. It's sort of, I call it, an orange peel approach to taking off the surface of the globe and flattening it out in a very artificial way. 

>> You never can quite flatten it out. But this is a very interesting attempt to achieve that. >> It has the pole zone too, doesn't it? The polar map. >> In 1514, when he is supposed to have made this, he has Antarctica. >> Yes. That's fascinating. >> And so, just to summarize, this is my attempt to bring all these characters from the 15th century and before to life as epitomized by this painting of all the philosophers by Raphael, The School of Athens. And in the center of this is a painting of Leonardo da Vinci represented himself. >> I think we've got a detail here. >> Yeah. 

So the man on the left is the representation of Leonardo da Vinci, and my own identification is that the bearded chap in the background may be Masolino. >> Well, it's the kind of thing that's very tempting, and also the kind of thing that will keep artists and art historians and also people in your line of work occupied for a long time to pin down and compare the images of who's who. >> Exactly. >> But this summarizes in the sense that we know these people were, in effect, learning from each other and that they were all working very hard to create the sense of space in a two-dimensional medium. >> And they were very much a community of people who knew each other and were all trying to impress each other with their latest works. >> Well, thank you very much for impressing me with some of your work. Christopher Tyler, it's been a pleasure. >> Thanks very much. >> I'm Norman Gilliland, and I hope you can join me for the next episode of University Place Presents.