Gurney Journey | category: Visual Perception | (page 15 of 15)


Gurney Journey

This daily weblog by Dinotopia creator James Gurney is for illustrators, plein-air painters, sketchers, comic artists, animators, art students, and writers. You'll find practical studio tips, insights into the making of the Dinotopia books, and first-hand reports from art schools and museums.

Getting a Fresh Eye

When I work on a painting I literally get too close to it, and I grow accustomed to its faults. There are at least six ways to get a fresh eye on a work in progress.

1. Turn it upside down and look at it (or work on it) inverted. I spend about one-fourth of my painting time working on my fantasy paintings inverted, either to see them objectively or to get a better angle on the strokes and perspective lines.

2. Step back from it, squinting and tilting your head.

3. Use a reducing glass—a double concave lens that will make your full composition fit handily into the palm of your hand.

4. Shoot a digital photo of the painting and look at it in the LCD, flip it 180 degrees or process it in Photoshop to see how it works in two values.

Getting a Fresh Eye5. Set up an adjustable mirror on the wall behind and above your shoulder (see above). Mine is mounted on a wall bracket with an adjustable ball in socket joint. Making the painting both smaller and reversed will help you spot problems right away.

6. Ask a trusted friend, family member, or visitor to take a look at it. They don’t have to be an art expert. What interests me most about someone’s reaction to my picture is what strikes them first, what they notice most. It’s not always what I was intending.

Bleaching and Glare

Bleaching and GlareWhen sunlight is extremely bright, the eye is dazzled for a moment. It takes a few seconds for the pupils to constrict. The cones are overwhelmed. Color response drops off in the brightly lit areas, and the shadows appear higher in chroma. This is the reverse of the normal rule of “color obtains in the light.”

Bleaching and GlareBefore Impressionism there was a movement called “The Glare Aesthetic” where artists used this bleaching phenomenon to convey bright light.
GJ post: "Color Obtains in the Light," link.
Top painting is by William Paxton (1869-1941) called the Chinese Parasol (1908), link.
Bottom painting by William Picknell (1853-1897), Road to Concarneau, link.
Chapter on the glare aesthetic in American Impressionism by William Gerdts, link.


What is going on in your brain when you behold the Pietà by Michelangelo?

NeuroestheticsOn one level your brain instantly perceives the shapes and contours, and it recognizes that the image on your computer screen is a photograph of a three-dimensional form. Even if you had never seen it before, you would recognize that the sculptural form represents human figures. You might observe that the sculpture is accomplished at the highest level of mastery. The subjects portrayed are not just any humans, but Mary and Jesus, with all the emotional and spiritual associations that go with that story. Perhaps you might recall the mentally disturbed geologist who vandalized the work with a hammer in 1972.

When I saw the Pietà in person, I was overcome by its beauty. I remember the feelings welled up inside me. I choked up, my eyes filled with tears, and I was unable to speak.

All these responses to a work of art can be studied using the new functional MRI (fMRI) mapping techniques. Corresponding with each level of response, there is specific and localized electrical activity going on in different parts of the brain.

NeuroestheticsTraditionally, the study of how and why we respond to beauty has been addressed by the field of aesthetics, a domain of philosophy. But today, a small group of scientists is working to understand aesthetic response in neurological terms, and this is part of a larger movement called “empirical aesthetics.”

One of the pioneers in this new field of neuroesthetics is Professor Semir Zeki. He coined the term, and he runs the Institute of Neuroesthetics at University College London. In his Statement on Neuroesthetics, he says, “Art is a human activity and, like all human activities, including morality, law and religion, depends upon, and obeys, the laws of the brain.”

Professor Zeki graciously responded to a few questions:

JG: Can we tell from brain imaging that the response to art is somehow special or different from the response to utilitarian or nonesthetic objects?

SZ: At present it is difficult to tell the difference between the response to an ordinary object (eg. a chair) and the response to viewing the painting of a chair. The same applies to faces. If, however, one were to focus specifically on the aesthetic value of what is being viewed, one would (I think) be able to differentiate between the two - assuming that the painting has greater aesthetic appeal. This is because, in that case, there would be greater activation of the orbito-frontal cortex.

JG: Tolstoy’s definition of art involves one person consciously infecting another with an emotion. When a subject reports that a work is beautiful or ugly, how is the brain’s emotional center involved?

SZ: Perceiving something as ugly or beautiful involves activation of the medial orbito-frontal cortex. Activity here is much more pronounced when pictures considered to be beautiful are perceived (in other words the activity is proportional to the declared experience of beauty).

JG: Walter Pater said that all of the arts aspire to the condition of music. Can we tell from fMRI studies how the response to visual art actually compares to the response to music or literature?

SZ: This is a question that I cannot answer at present. It is nevertheless an interesting question, worthy of future study.

JG: Does the brain respond differently to abstract versus representational art?

SZ: Yes, it seems to. Portrait paintings activate a specific part of the brain, landscapes another, and still lifes yet another. Abstract art seems to lead to very little activation, presumably because in the contrasts used to elicit the activation, the ubiquity of what is shown in abstract paintings (that is to say the features there that are also common to landscapes and still lifes and portraits) lead to activity being cancelled out in the subtraction process.

JG: How would you respond to critics who say that this line of inquiry is too reductive and diminishes the mystery and grandeur of the aesthetic experience?

SZ: I would say that they are misguided, because knowledge of the mechanisms involved in artistic appreciation and creativity does not in the least diminish the affective value of these works when we view them. I would also say that they are misguided to think that there can ever be a satisfying theory of aesthetics and beauty which does not take into account the neural activity which leads to aesthetic experiences. I would finally say that, whatever their concerns, science has now embarked firmly on a study of neuroesthetics, and there is no turning back.

Professor Semir Zeki's blog and website. and his statement on neuroesthetics.
Wikipedia entry on Neuroesthetics, link
Association of Neuroesthetics website, link.
More about fMRI, link.
Image of brain from:
More about the Pieta and its vandal, Laszlo Toth, link.

Never Forget a Face

Never Forget a FaceAccording to a recent study by Kim Curby and Isabel Gautier of Vanderbilt University, we can remember faces far better than, say, wristwatches or cars.

Never Forget a Face“Our results show that we can store more faces than other objects in our visual short-term memory,” says Gauthier. “We believe this happens because of the special way in which faces are encoded… Being able to store more faces in VSTM may be very useful in complex social situations.”

Addendum May 17
I was intrigued by Erik's comment about hair and beards, and noticed the lack of them in the pictures that were used for the experiment, so I asked Dr. Gautier the following: "Have you factored in the role that hair or beards play in facial recognition? Does it code or store differently from other features given that it can be more variable?"

She replied: "In general, our work and that of others focuses on mechanisms that appear to distinguish face processing - the internal features of faces are processed in a more holistic manner (not as parts, but as a whole) than other objects. In the context of experiments where we only use a limited number of faces, hair might be SO helpful that people would rely on it entirely and we could not study how internal features are processed - so they are generally excluded."

Vanderbilt University report, link and article in Science Daily, link.

Edge Induction

It was twilight in Tannersville, New York. A light rain had been coming down steadily all day. I set up my easel under a store awning because I stupidly forgot an umbrella. The aroma of French onion soup beckoned from the restaurant across the street.

Edge InductionThe sun must have set by now because the light was failing. The light from the sky seemed to have bluish cast in contrast to the warm lights that were coming on. But I wasn't sure. I could practically feel the cones in my eyes shutting down. Honestly I could hardly see what colors I was mixing on the palette, because I forgot a flashlight, too.

As I studied the scene I realized that I could easily see the sharply defined contours of the utility pole and the roofline against the bright sky. But I couldn’t make out the clapboards or the signs; in fact I really couldn’t see the windows or doors at all—except on the bright white building in the center of the picture. So I tried to paint the scene as I saw it: blurry and tentative.

Edge InductionThis illustrates a principle called “edge induction.” When a subject is poorly lit or in shadow, some of the edges will be below the threshold where our eyes can discern a contour. A camera might be able to pick up all the edges in these dim zones, but not the human eye.

It's not just a matter of what the rods and cones can respond to. What happens without you knowing it is that your brain takes over where your eyes leave off. In dim conditions your visual cortex starts interpolating or inventing contours based on the few edges that you truly can see and on your prior knowledge of how things should look.

The brain wants to confirm the contours first, and then it quickly fills them in with textures, tones, and colors—almost like a coloring book. This happens instantly at an unconscious level, as was demonstrated in a study published last summer by researchers at Vanderbilt University.

The visual cortex is always busy constructing a detailed fabrication of the world, whether it has all the information or not, and it tricks you into thinking you’re seeing edges that really aren’t visible.

Edge InductionPainters shouldn’t seek out edges that aren’t there; in fact poetry often springs from deliberately placing edges into obscurity, as Meissonier did in this portrait of Dumas.

Edge InductionLet edges and details go out of focus in sub-threshold or shadow areas, as Gerome did with the shadow-side eye in this portrait of a peasant. If you like a painterly handling, here’s the place to use sketchy, soft brushstrokes. It’s perfectly OK to deny the viewer the chance to scrutinize the details too much.

For more about that Vanderbilt University study and the phenomenon of edge induction, link.
The last three images came from Art Renewal Center, link.

Tomorrow is the Art by Committee sketch challenge. Please get your sketches in by Tuesday at 6:00 pm. Eastern Time, USA. To read about the challenge, link, and then scroll down.

Is Moonlight Blue?

Moonlight is about 400,000 times weaker than direct sunlight. It’s so dim that the color receptors in our retinas, called the cones, can barely function.

In moonlight the other retinal cells called rods are doing most of the work. Rods detect relative lightness and darkness, but they are entirely color-blind.

Is Moonlight Blue?
Moonlight is simply the white light of the sun reflecting off the gray surface of the moon. There’s nothing in that interaction to give the light a bluish or greenish quality. In fact, scientific instruments have shown that the light from the moon is very slightly redder in color than direct sunlight.

These facts added together suggest a mystery at the heart of how we as artists choose to portray moonlight in paintings. If moonlight is just gray-colored light, and if it’s close to the minimal threshold of our color receptors anyway, then why do so many artists paint moonlight as bluish or greenish? Do we really see it that way? Is it some kind of illusion, or perhaps is it just an artistic convention?

Let’s look at some paintings by master painters of moonlight. As you look at them, consider your own perception of the colors at night, and ask yourself which of the paintings best convey your own experience.

Is Moonlight Blue?Here’s a painting by J.M.W. Turner. It’s fairly gray, with just a hint of warm color around the moon. Notice that there isn’t much detail in the shadow area. All you really see clearly are the silhouettes of the sail and the boat on the water.

Is Moonlight Blue?
Russian seascape painter Aivazovsky painted this night scene lit by a golden moon. The sky, the water, and the shadows all sink into blue-green tones. He doesn’t show very much detail, and he stops well short of black in the shadows.

Is Moonlight Blue?
This lightening of darks was also a feature of Remington’s nocturnes. The cast shadow to the left of the pony’s nose is composed of dull umbers and greens. These luminous shadows lighten and liven the obscurity. Except for the light saddle cover, Remington has left most of the edges soft and undefined, especially on the donkey on the right.

Is Moonlight Blue?
This famous nocturne by Whistler of the Battersea Bridge uses a fairly saturated blue-green color, especially in the water and in the silhouetted figure. The detail is blurred throughout, even in the areas where the bridge appears against the sky, setting up for the tiny sparkles of light in the distance.

One of the reasons for softening the edges is that we depend on the cones for fine discrimination of edges. Unfortunately the cones are located on the fovea, the centerpoint of vision, and with them off-line in the darkness, we just can’t sort out small details.

If you take a book or newspaper outdoors in moonlight, you can see that there is writing on the page, and you might be able to read headlines or other large type, especially when you glance around with your peripheral vision. But reading normal size text is almost impossible. When you look directly at the words, the blind spots get in the way.

I said earlier that our cones are barely functioning in moonlight. In fact, contrary to what some authorities have claimed, most people’s cones can make basic color judgments by the light of a full moon. But how much variation in color can we really see?

Is Moonlight Blue?
Maxfield Parrish rendered this moonlight scene with quite a bit of color saturation. He painted the yellow moonlight, the reddish cupula on the barn, the deep blue of the sky, and the orange color on the shadow side of the house. Did he really see such colors in moonlight, or did he invent them for pictorial effect? Too bad he’s not here to ask.

Direct plein-air painting is virtually impossible in moonlight. Every artist has to work from memory and imagination. We may try to convey our actual optical sensations, but we’re not scientists. Each of us is also trying to make a subjective aesthetic statement intended to evoke a particular mood or emotion. Any moonlight painting is an attempt to translate a “rod experience” into a “cone experience,” an image that will be seen in a brightly lit environment.

Is Moonlight Blue?Here’s how you can test how your cones actually respond to color in moonlight. Paint a set of separate, matching, unmarked color swatches or find some construction paper at about the same value. Take them into full moonlight (this Tuesday) and let your eyes adjust (it takes about 30 minutes). Shuffle the cards, and while you’re still outdoors, mark on the back what colors you think they are.

Is Moonlight Blue?I have used Photoshop to manipulate a photo of the swatches (actually shot in daylight) to simulate how they appeared to me under the full moon: dulling, darkening, and blurring them. Both Jeanette and I could easily identify the basic hue family of each swatch. But beyond that basic classification, we weren’t sure, and the gray swatch confused us both.

When I looked at the same swatches in the much dimmer light of a half-moon, or in a moon shadow, I found my cones went sub-threshold and shut down completely, and the swatches became completely monochromatic.

Although the rods of the eye can’t actually see color, scientists have shown that they are most sensitive to greenish wavelengths of light. As a result blue-green hues appear lighter in tone in dim conditions. There’s a name for this: the Purkinje Shift. It’s a different phenomenon from, and often mistaken for, the perception of moonlight as blue.

You can demonstrate the Purkinje Shift by comparing a red and green swatch that start out indoors at the same value. If you take them outdoors in moonlight, the greenish one will seem much lighter in tone. Many observers have noticed that red roses look black in the moonlight.

If you scroll back up to my Photoshopped version of the moonlight color swatches, you can see I’ve adjusted the values to simulate the way the red and green looked to me as a result of the Purkinje Shift.

Is Moonlight Blue?
Here, Remington shows a scene with Indians in moonlight. We see their flesh tones and some clear red touches in their costumes. Throughout, the edges are much crisper than his other painting.

Is Moonlight Blue?This nocturne of old Cincinatti by contemporary artist John Stobart has a distinctly bluish cast. He introduces much more detail than we’ve seen in the other examples, reminiscent of the “day-for-night” film shoots in old westerns. You can even read the name “Bonanza” on the shadow side of the ship.

In addition to the moonlight, there’s a secondary source of yellow-orange lamplight. In this case, one could argue that the blue cast to the picture may be a complementary color induced in opposition to the color of the lamplight.

Is Moonlight Blue?Atkinson Grimshaw was famous for his poetic moonlight studies. Here the shadow masses at the left are fairly soft and impenetrable, but the bricks and branches show up very clearly. The moonlight on the road is an intense yellow-orange, assuming this reproduction is accurate. The shape of the patch of light points to the lovers standing in silhouette at left.

Is Moonlight Blue?
Russian landscape realist Ivan Shishkin, painted this haunting image of a winter night in the wild north. The snow in moonlight is relatively brilliant, with a soft halation along the edge at left, but it’s not yellowish. The cast shadow gradates in tone, getting lighter as it catches more sky fill and bounced light. There’s quite a bit of detail in the tree form, but he has kept the foreground and background description to a minimum.

So, to get back to the question posed earlier, why do we see moonlight as blue?

Saad M. Khan and Sumanta N. Pattanaik of University of Central Florida have proposed that the blue color is a perceptual illusion, caused by a spillover of neural activity from the rods to the adjacent cones.

Is Moonlight Blue?A small synaptic bridge between the active rods and the inactive cones touches off the blue receptors in the cones, kind of like an insomniac turning over in bed and rousing his sleeping spouse.

This influence of rod activity on the adjacent cones tricks the brain into thinking we’re seeing blue colored light, even though we’re really not.

As the authors put it: “We hypothesize that the rod cells predominantly synapse onto the S-cone (cone cells sensitive to bluish light) circuitry resulting in the visual cortex perceiving a tinge of blue.”

Is Moonlight Blue?
So moonlight isn’t blue; our eyes are just playing tricks on us.

Unfortunately, this tantalyzing hypothesis remains untested. I contacted Dr. Khan and he told me that because of other projects he hasn’t had time to prove the hypothesis in controlled conditions. I hope that he can shed more light—of whatever color—on this elusive topic.

Until then, moonlight remains a mystery at the meeting point of art and science.

Further reading:
  1. Khan and Pattanaik’s summary article in Journal of Vision, 2004. Link.
  2. Related discussion on the NASA web site. Link
  3. "The Eye and Night Vision," from American Optometric Association. Link.
  4. More on Remington’s nocturnes at David Apatoff's blog. Link
Tomorrow: Elegant Graphics
Getting a Fresh EyeBleaching and GlareNeuroestheticsNever Forget a FaceEdge InductionIs Moonlight Blue?

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