Discovering the Third Dimension

Pre-renaissance artists had trouble with depicting depth in their paintings. Can you find some examples of this? How did their paintings fail to depict depth? What aspects of a painting give it depth?

Das Paradiesgärtlein, dating from the early fifteenth century, is an example of a two-dimensional painting that lacks the illusory power of creating a third dimension that is achieved more successfully in later paintings. What does this colorful, creative work lack that its successors would gain? The answers can be found in monocular cues – that is, visual depth cues that do not depend on the binocular power of stereopsis. They include:

1. Occlusion – better known as overlapping. The painting shown uses this technique well to create a sense of depth: flowers arch in front of the garden wall, a lady holds a book before her, a man hides behind a tree trunk, etc.

2. Size – in the painting, this depth clue is all about relativity and scale. Objects that are normally larger or smaller than other objects must retain that proportional size. Furthermore, variations in size due to depth or distance must also be included. Thus, a man must be shorter than a tree unless he is portrayed as much closer to the viewer than the tree, for example. In the painting, the latter of these size-rules is not followed as well. The flowers in the background, against the garden wall, are almost as tall as the women in the foreground.

3. Perspective – objects lessen in perceived size and rise in perceived horizontal location as they recede into the distance. As already discussed, the size scale is a bit off in this painting; objects don’t really lessen in size in the background, and may even be irregularly large in the first place. The rising-rule is followed a bit better: the garden wall, which is the furthest object in the picture, is near the top of the canvas, while the people are scattered through various latitudes. However, the overall placement is a bit extreme, and the extremeness is accentuated by the objects’ oddly uniform size.

4. Shading – shadows signify the location of a light source and show where light is lacking, thus conveying the three-dimensional shape of objects. There is some light shading in the painting, such as in the ladies’ skirts, but not as much as we would perceive in the natural world.

Overall, the painting relies on overlap, an exaggerated rise toward the horizon, a bit of shading and the brightly colored, clear-cut figures of the objects to convey the idea of separate images that recede in depth. However, while this painting is lacking in some ways, it is much more realistic than its predecessors and would be followed soon by surprisingly real achievements.

Das Paradiesgärtlein (The Paradise Garden), c. 1410

Final Blog Entry

It sounds a bit crazy, and maybe unsympathetic, but I always enjoy hearing about perception-related disorders. They reflect evidence and embodiment of what we have learned, and they may also just be strange, opening up our eyes to new perspectives, to different ways of living life and functioning in this world.

The most fascinating disorder that I read about this semester was Anton’s syndrome. Blake describes Anton’s syndrome as “a neurological condition in which a cortically blind person denies his or her blindness.” In one of the quirks of the human brain’s structure, the cortical area for visual processing is separate from the cortical area for visual awareness. If both are damaged at once, Anton’s can result.

Apparently the only way for someone with the syndrome to realize and accept their blindness is through physical trial-and-error: they describe what they are “seeing” with confidence (which is inaccurate), but eventually have enough trouble navigating to evoke doubt.

On the site ScienceIQ.com, David Gamon discusses some of the peculiarities of the condition: “the really weird thing about it is that they’re not lying… they really are convinced that they can see.” Conscious awareness and reasoning are completely disconnected from actual physical perception.

Or, perhaps, are these people still actively seeing, just seeing in a different way? We have discussed color-blindness, and how people who are color-blind still see the world, just not as the majority of humanity sees it. And we have discussed how some animals have only one or two cone pigments, and some have eyes more laterally placed on their heads. Is Anton’s just another mode of sight? Or another deficit of the visual system, like blind spots?

I’d have to say no. The examples described are biological differences derived from differences in receptors; Anton’s is caused by neurological damage. And deficits are evolved so that the brain has adapted to them, and can manage to work around them, whereas Anton’s is a complete and sudden loss of accurate visual information. People with Anton’s aren’t just perceiving the world differently – say, through a different filter; the neurological signals they are processing are misfires.

To an English major like myself, I see something almost comically literate about such a condition: the disconnect between reality and perception, between the internal and external, etc. It seems like someone should write a story, or at least a TV episode, about it. In the end, though, I’d have to say I’m grateful that it’s one more disorder that I don’t have to actually deal with myself. Functional perception is a useful thing.

Color-Math

What is the difference between adding and subtracting colors? What does that even mean?

Sometime around kindergarten, we learn that there are three primary colors – red, yellow, and blue – and that mixing red and yellow paint makes orange paint, red and blue makes purple, and yellow and blue makes green. Sometime later – sixth grade science, perhaps – we learn that light has different primary colors: red, blue, and green. But color is made of light, right? How can these two rules be reconciled?

There is a difference in primary colors and their resulting mixtures because of what the forms of color do. Paint is a material that changes the hue of color that is reflected from the paper. For example, white paper reflects all colors; putting yellow paint on the paper means that only yellow light is reflected. When the yellow is washed over with blue, the only light that is reflected is the light in the color spectrum that borders on both yellow and blue: green is left. And when green is washed over with red, only brown or black is reflected. This narrowing, decreasing range of color hues reflected from the painting – starting at white and progressing to black – is an example of subtractive color mixture.

Imagine the opposite scenario. You start with a dark space; no light shines into it. It is black. Next, a green light is switched on. The space is lit with a green hue. Then a red light is turned on. The space becomes yellow: more wavelengths of light are available. Finally, a blue light is turned on. The space is filled with white light, because it contains all of the wavelengths of light visible to the human eye. This process of light addition – starting at black and progressing to white – is an example of additive color mixture.

Therefore, in subtractive color mixture, more and more light is absorbed when colors are mixed. In additive color mixture, more and more light is reflected or produced when colors are mixed.

Nature v. Nurture in the Visual System

How does the nature versus nurture debate come into play in the development of a normal visual system?

One example of the nature versus nurture debate arises in the phenomenon called the “oblique effect.” The oblique effect refers to the visual system’s preference of horizontal and vertical lines to oblique lines. On page 129 of Blake, one can see a diagram of the unequal distribution of cortical cells to various preferred orientations.

The nature versus nurture question in this case is whether this cell distribution arises naturally from our genetic code, or whether the distribution is an adaptation to the environment we are exposed to during development. Research has shown that our environments do have a natural bias toward the visually horizontal and vertical. However, the development of this cell distribution occurs very early in our overall development – within our first few months, in fact.

According to Blake, the generally accepted view of nature versus nurture in this case is similar to the overall view of nature versus nurture which most scientists hold: both genetic and environmental factors influence our development, and so neither can be separated from the other or ignored as irrelevant.