Friday, November 25, 2011


You will perhaps remember that when we left off talking about Ingres, we were discussing the implication of form and volume in drawings of his like this one:

To continue, a little bit of neuroscience, courtesy of Dr. Margaret Livingstone.

In her marvelous book, Livingstone describes two evolutionarily distinct systems of visual processing in humans, which she calls Where and What. Where is a primitive system, shared with many mammals and tuned to movement and location. The younger What is a sophisticated system shared only with primates. It is responsible for object recognition and detail analysis.

What itself is subdivided into Form and Color (her casual names, it should be noted, do describe anatomically and functionally distinct structures).

Form is a high-resolution part of the system, using color differences and brightness differences to determine the shapes of objects. Color identifies the colors of objects, and it is surprisingly low-resolution.

As a matter of information processing efficiency, our brain basically produces a colorless high-resolution image, then smears some colors onto it, much like a painter proceeding from a well-defined grisaille underpainting to a hastily-completed color painting. This resolution difference has been exploited in video technology with the use of 4:1:1 color space. 4:1:1 is a data-compression system in which the brightness of each pixel of a frame is defined individually, but color is defined in blocks of four pixels:

4:1:1 saves a lot of space in a video signal, and interfaces perfectly satisfactorily with the lopsided resolutions of our Form and Color systems.

This simple general description unfolds, of course, to reveal all kinds of fascinating quirks. When we were talking about Ingres a few weeks ago, I made vague reference to how the heavy dependence on line makes unusually extensive use of "the information-completion procedures of the visual brain." By now, you should know that I don't especially like vague references. So I've been thinking about which exact procedures I'm alluding to, and this led me to re-consider one of the quirks of Form/Color integration in the evolved What system of the human brain.

In chapter 11 of her book, Livingstone gets into the nitty-gritty of how the separate information feeds from Form and Color are re-integrated to produce a coherent image in the mind. One of the topics that arises is color and edges. It turns out that part of the edge-detection machinery we discussed a while back results in our being strongly sensitive to colors at the boundaries between regions of unlike color, and weakly sensitive to colors in homogeneous color fields.

(As an aside, this gives us some insight into the sense of suggestion in Rothko paintings:

Mark Rothko, No. 14, 1960, oil on canvas, 114 1/2 in. x 105 5/8 in.

By producing nearly, but not quite, homogeneous color fields, he is producing the visual equivalent of a sound one cannot quite make out. He causes us to strain at the limits of our sensitivities, becoming awake to subtleties which we ordinarily fail to perceive. His fields begin to shimmer with suggestion, with the evolving interaction between true presence and phantoms.)

But back to the point - we are sensitive to colors at the edges, not the centers, because of the edge-detection machinery of our visual systems. Our brain compensates for this physiological deficiency with a truly ridiculous trick: Autofill (my own sarcastic term, not Livingtone's). We see, for instance, a red apple as totally colored in part because our brain, receiving a "red edge" signal, fills the interior with red:

You see how you kind of see the interior of the bottom apple as reddish? I don't mean full-on red. But it doesn't look like the same white as the background. And yet, it is. That's "the information-completion procedures of the visual brain" I was talking about last time. Wild, huh?

Livingstone, wise in the ways not only of neurons but of paintings, illustrates her point with this Cezanne painting, The Lime Kiln (1890-94):

Cezanne, it would appear, was the man at exploiting this particular visual system quirk. All artists hack the human visual system at one or more points of weakness. Cezanne enjoyed using Autofill. Consider his apples as well:

Cezanne, Still Life with Apples, 1890-94, oil on canvas, 18 1/8 x 21 5/8 in

Observe how he darkens the edges, and makes the colors more rich at the edges. This is not an outcome of the frontal lighting alone. It also answers to visual integration in the brain, producing a startlingly vivid sense of presence by reinforcing the mechanisms of the Form and Color systems.

The presence overwhelms that of more realistic depictions of fruit - Hockney points out the relative lack of vividity of Caravaggio's fruit:

Caravaggio, Basket of Fruit, 1597

Why? In part because Cezanne has amped up color and contrast. But also, because he is depicting not only what we see, but how we see it. We are observing not the external world, but the partly-garbled outcome of our means of perceiving the external world. The painting, in a sense, is already inside of us: what was inward has been made outward. He speaks to us, mind to mind, soul to soul. These apples are icons not only of matter, but of consciousness. I have discussed this concept with you before - a painting which is not biologically alive, but is in a metaphysical sense at the boundary of being a living thing. It is excavated from the depths of the mind, and shaped as it is by the processes of the brain, correlates with no thing in the physical world.

Now, I'd like to extend Livingstone's claim with a little experiment. Let's look at the same apple comparison with the color removed:

Huh, that worked. I just did this in Photoshop myself - you and I, my friends, are the laboratory for this experiment. You see how the interior of the bottom apple looks faintly darker than the background? Autofill is still working. If it's the same Autofill Livingstone describes, what this means is that the Color system doesn't depend on actual per se color to signal the mind to see a continuation of edge color. It just needs a value difference delineated by a sharp boundary on one side and a soft boundary on the other.

Now let's see what happens when I try this:

Yes! It works! OK, notice how the white region of the right half of the apple looks a little darker than that the of the left half? Almost as if a slice had been taken out of the left half, so that you were still seeing the apple's skin on the right, but the flesh of the apple on the left? Of course, all of that interior is exactly the same shade of white.

What we've done here is evoked a complex response on the part of Autofill. On the left, there is an edge, but no interior gradient shading to instruct the system to autofill the interior of the apple. On the right, the gradient shading does deliver the autofill-interior-of-apple instruction. Overall, we know the apple is one closed form. But our brains are treating it as having two different color regions, resulting in perception of two different interior brightnesses; even if we can't quite tell where the boundary lies, there is a distinction.

Forgive me if you've already deduced where I'm going with this. We are treating a simple example here, but an example with the markers I wanted to explore: a figure depicted on a white field by means of outlines of diverse qualities. Having demonstrated the principles involved in a simple system, we can extend the conclusion back up to the real system of interest:

Like Cezanne, Ingres has hacked Autofill. His variation of line is delivering a series of instructions to the Color system to observe value differences which are, for the most part, not actually depicted in the drawing. These value differences are interpreted by the mind as depictions of form. Ingres is using his mastery of line to trick the brain into seeing imaginary forms.

And that, my friends, is what makes Ingres a master and you and me a couple of shmucks with an art supply store discount card.

Let me add one more thing before signing off: I am not immune, as perhaps you are not immune, to the persistent worry that one can strip the mystery and beauty out of art by looking at some facet of it and finding out what it is and how it works. Reflecting on the matter, I have reached this formulation: that to know what it is and how it works is not the same as to know what it means, or why. We can - indeed, as working artists, to some extent we must - find out how to achieve the effects we intend. But to learn these things, even in the painfully analytic manner of this blog, has never breached, nor can ever breach, the muscular bond between the image in the eye and the sensation in the soul. Ingres, Cezanne, Rothko, and Caravaggio come through this examination intact, because when we look at them, we are not seeing with our analytic understanding alone. Indeed, for me, this additional element of knowing serves only to reinforce the impression - "How miraculous is their work, and how miraculous are we, to see things as we see them."