Gurney Journey | category: Visual Perception | (page 4 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.


Phosphenes are apparent flashes of of light that appear without any light coming into the eye. They can occur when the eye is stimulated by mechanical pressure on the eyeball, with electrical stimulation of the visual cortex, or just by means of random firing of cells in the neural system.

Here's an explanation (Link to video), along with a way to demonstrate the blind spot illusion.

Phosphenes can be experienced by people who have been blind from birth when their brains are stimulated directly, or by people confined for long periods in darkness (where the effect is sometimes called "prisoner's cinema"), and by people experiencing hallucinogenic drugs.
Wikipedia on Phosphenes


Look at the circle of red dots with your eyes relaxed. It is surrounded by a ring of blue dots against a black background. 


Does one group of dots appear to come forward or rise above the other? Is there any apparent lateral movement of the dots in relation to each other?


Here are some horizontal stripes: white, black, yellow, and blue, with a stonework texture throughout. Does the figure look flat, or do some of the stripes seem to advance forward toward you, like shiplap siding? 

About half of the viewers of all of these illusions perceive the warm colors to be coming forward relative to the blue and black colors, and many see other movement happening. Some people see the reverse: the blue parts ahead of the red or yellow 

These figures were created by Akiyoshi Kitaoka (link to website) to illustrate chromostereopsis, a phenomenon where warm colors seem to come forward while cool colors appear to recede.


Early stained glass windows suggests that artists have used the effect to create the illusion of depth in a 2D surface.

According to color expert David Briggs, "This phenomenon results from the effect on our stereoscopic vision of the different focal points of long and short wavelength rays, causing a red object to appear to be on a distinctly nearer plane than an equidistant blue object for the majority of observers." 

What is the complement of blue?

Chris says: "James your explanation of the Yurmby wheel in your book Color and Light changed my life. It's such a great way to make cohesion in the palette as well as knowing how to move a color. What always gets me though is how do you make grey from yellow and blue, that part of my mental wiring is the last hold out."

Chris, you're right to wonder about that. If you mix yellow and blue paint, you get green, not gray. However, in the machinery of the eye, a royal blue is opposite to yellow (not orange). You can test this for yourself by looking at a blue square for 30 seconds, and then let your eyes move to the white area below it. 
What is the complement of blue?

What is the complement of blue?

 What color did you see in the white box? Most people see yellow, not orange.

It turns out that complements are different in additive mixtures (the realms of visual perception, theater lighting, digital art, and camera sensors) than they are in subtractive mixtures (pigments).

What is the complement of blue?
J.M.W. Turner, Norham Castle, Sunrise
The argument for thinking in terms of the additive (blue-yellow) complements when painting is that you might as well optimize your final image to the behavior of the eye rather than to the behavior of the pigments, because that's what matters to the viewer's experience.
Read More: 
Previously on this blog: The Color Wheel, Part 3: Complements and Afterimages
On the excellent website: HueValueChroma: Additive Complementaries
On the excellent website: HueValueChroma: Subtractive Complementaries
Color and Light

'Facephenes': Hallucinations of faces, stimulated in the lab

Images courtesy Schalk and Discover Magazine
Facephenes are hallucinations of faces caused by stimulation of the face-recognition area of the brain.

Link to Video on YouTube
The patient was a epileptic Japanese man outfitted with a large number of brain electrodes to find the source of his seizures. He described the experience: "Your face changed completely," he said. “I don’t know what’s going on. Your eyes…change.” Sometimes parts of faces emerged, and at weird angles, and other times an anime-like character appeared over the background object.

It appears that facial recognition skills in the brain are primarily situated in the lower, lateral areas of the brain, right next to areas that play an important role in color perception, so when the stimulation moved over a bit, rainbows instead of faces appeared.

From the researchers notes to the YouTube video:

"The human brain handles several mental processes and cognitive tasks like the visual perception of the environment. Many studies investigated the role of individual brain regions during dedicated mental processes and tried to understand whether a specific brain region is exclusively engaged in such a process. In a recent study we partly answered that question by electrically stimulating the ventral temporal brain of a patient who underwent surgical treatment of epilepsy. Electrical stimulation of color- and face-selective sites, which were identified by means of visual evoked responses in the brain waves, affected only color and face percepts, respectively. The reported symptoms included illusory faces on top of objects and changed perception of faces during stimulation of face-selective regions, and the appearance of illusory rainbows near color-preferring sites. These findings support the theory that the brain at least partly consists of specialized regions that are exclusively and causally engaged in a dedicated mental process."

A key question posed by Neuroskeptic is whether the faces seem "superimposed over" the objects, or whether the objects appear to have the faces integrated into their forms. If they ever try an experiment like this on an artist, they'll get a much clearer description of the experience. 

Discover Magazine “Facephenes”: Brain Stimulation Creates Phantasmal Faces
IFL Science: Brain Stimulation Causes Man to See Ghostly Cartoon Faces Everywhere
Today, October 26, is the last day of the "American Masters" exhibition in New York City
I'll be giving a talk in Austin, Texas on Monday. Open to the public, but reserve your spot.

Art is a record of selective attention

Painting in Rawlins, Wyoming Watch the video on YouTube
Every painting is a window to another world. More than that, it’s a record of the artist’s awareness of that world. It’s a document of reality as filtered through one person's consciousness.

This way of looking at drawing or painting is based on the "filtering" or "gating" models of perception that have arisen in neurobiology in recent years. You might think of it as a modern way of expressing Emile Zola's 1866 idea that "art is a corner of nature seen through a temperament."

Sensory gating theory proposes that we screen out the majority of information that surrounds us at any given time. The classic case is a cocktail party, where you focus on the conversation, while your brain discards the bulk of other sensory information. That other information is mere noise that might otherwise distract you from the signal.

Another famous example of perceptual gating is the "Gorilla Experiment." In this demonstration, the observer is asked to count the number of times a ball is passed back and forth. While you concentrate on that task, other things happen that you might not even notice.

In our normal daily life this gating is achieved for the most part automatically. But attention can be distributed consciously and selectively, especially with practice. As artists, we learn to control the perceptual filters that we use, and we deploy them at will. Essentially, this is exactly what we're trained to do whenever we paint or draw.

For example, at the beginning of making a picture, we gate our perception to notice only the perspective, the proportions, the relative measurements, and the slopes of the lines. During these early stages, we ignore such things as colors or edges or textures. As the painting progresses, we shift our attention to notice other aspects of the scene, shifting back and forth between noticing big shapes and small details. A classic beginner's mistake is to paint the eyelashes or buttons at the very start.

Ernest Meissonier, An Artist Showing His Work
In the midst of this process of filtering attention, we also enlist our emotions, because art-making isn't just a technical trick. We may have some personal connection to the subject. We might be looking for what pose is characteristic. Something might strike us as funny about it. Or the subject might impress us as scary or unsettling. Consciously or not, those emotions will drive choices of what elements we allow to pass through the filter, and what elements get filtered out.

Whether the results are realistic or distorted, they strike viewers as "artistic" because we identify with the very human filters that the art has passed through. Art engages us in a kinship with each other because it allows us to pass through the doors of perception from one human soul to another. 

Making a Hollow-Mask Illusion

The "Hollow-Mask Illusion" involves tricking the viewer into thinking a negative form is positive.

Creating this effect involved:
1) Making a negative mold from the face of the original sculpt (which is by Jake Hebbert). I used Magic Sculpt for this.
2) attaching that to a positive sculpt of the base
3) Lighting everything in the scene - except the hollow face - with a light from the upper right. I used a gobo on a wire to block light on the hollow face.
4) Lighting only the hollow face with light from the lower left, using an oval mask to shield everything else.

A computer generated version of this is called the "Rotating Mask Illusion."

You can make your own interactive version of this out of paper. 
Magic Sculpt

What does eyetracking tell us about the rules of composition?

What does eyetracking tell us about the rules of composition?
Eyetracking heat map of The Last Supper by Leonardo da Vinci   
Artist and blog reader Eric Wilkerson asks:

     "I had a discussion with another illustrator over composition recently. Specifically about the usage of directional lines and shapes to lead the eye to the focal point of the painting or cinematic frame in a movie.
     "I know you refer to it as spokewheeling and shapewelding. I learned all this back in college and it was drilled into us based on the old Loomis books.
     "Anyway, my friend says that all of that is nonsense due to eye tracking and that it doesn't matter where the lines are going because the brain is going to look for a face or random points of interest every time.
     "So do you think eye tracking negates spokewheeling etc or is it all a combination of elements to lead the viewer through a composition?
     "I'm firmly in the camp that it doesn't. I've been studying the work of some famous cinematographers lately and they compose whole frames through use of strong light, shadow, color and directional shapes to lead the viewer.

     "I don't know....So I'm writing you. Hope you can settle this for me or at least offer some insight."

What does eyetracking tell us about the rules of composition?
Eye tracking scanpath  by A.L. Yarbus
on Repin's painting "The Did Not Expect Him"
Hi, Eric,
That's a fascinating question, and I'm glad you asked it. Here's the short answer: I believe that scientific insights from eyetracking challenges a lot of the art-school dogma about how we look at pictures. But don't throw out the compositional toolkit just yet. Many of those compositional devices are probably still valid.

What does eyetracking tell us about the rules of composition?
Eye tracking heatmap in a bar. Viewers apparently want to know
what brands of beer are on tap  
You and your friend are both right. Your friend is right that faces (or other psychologically important objects) will attract the most attention wherever you place them in the design. Eye tracking proves that. It also shows that the way each viewer explores the picture is highly individual. No two viewers will experience the picture in the same way.

What does eyetracking tell us about the rules of composition?
Venice by Turner. I'd love to see an eyetracking heatmap of this painting. I believe
 that I'm most attracted to the light buildings on the light background,
not to the areas of highest contrast. But maybe I'm misreporting my experience,
and maybe I look at this painting differently than others do.

The scanpath (the track of eye movements over time) of a given viewer depends to a great extent on what psychological or narrative expectations he or she brings to the interpretation of the image. Contrary to many dogmatic assertions that we learned in art school, the eye's path through the picture does not really follow passively along the directional lines. Instead it jumps around in unpredictable jagged leaps all over the picture. While we customarily speak about "leading the eye" or "forcing the viewer" or "directing the attention" by means of leading lines, we have to remember that the eyes are not driven in a deterministic way, like a train on a track.

Eyes are active extensions of a hungry brain.

Does this mean that those traditional compositional devices have no effect on our experience of the picture?

No, and here is where I think you are also right. I believe that most of the classical design devices (including  spokewheeling, chromatic accents, edge control, value organization, etc.) can influence the way we perceive a composition. When used intelligently, they can help the average viewer decode what's important in a picture, and they accentuate the viewer's satisfaction in having their attention anchored to the centers of interest as they further explore subordinate areas.
What does eyetracking tell us about the rules of composition?
Yarbus's data originally published
in "Eye movements and vision" (read more)

But it's difficult to know exactly how we're influenced by such devices. I suspect that we perceive them by means of our peripheral vision, even if we don't perceive them directly with our center of vision.

For example, let's look at the two paintings in this post. In "The Last Supper," Leonardo's placement of the vanishing point behind Christ's head seems to reinforce our focus on that important center of intererst.

But in the case of "They Did Not Expect Him," Repin doesn't place the vanishing point behind any of the major heads, but that doesn't seem to compromise the ability of viewers to find what is important in his painting.

Yarbus showed that people looked at the the Repin painting many different ways (right) depending on what question they were prompted with first.

Viewers are perhaps more influenced by leading questions than leading lines.

Science is beginning to reveal that visual processing of any image—but especially a realistic, narrative image—involves many areas of the brain. How we look at a picture appears to be affected by several interrelated factors, such as lines, tones, lighting, color, psychology, title, caption, and other factors. The leading lines and the shapes are just two of those elements.

My advice
Science can help us bayonet sacred cows, but it can't guide us very much in designing pictures. How we look at artwork is a topic that is still mostly unexplored by cognitive scientists using modern technology. Until more studies are carried out, we can't fully understand the logic behind pictorial design. My advice is to be skeptical when you hear any dogmatic assertions about composition. Instead, follow your instincts. Don't concern yourself with following compositional "rules," and don't bother with making your pictures pleasing or harmonious. Instead just work to make your picture interesting. Figure out what you want to say and say it emphatically.

If a graduate student in neurobiology is reading this and wants to devise some experiments, please contact me! I'll volunteer some of my paintings as guinea pigs.
More info
Previous posts:
Eyetracking and Composition (series)
Books: Vision and Art (Updated and Expanded Edition)
Imaginative Realism: How to Paint What Doesn't Exist

How do we look at architecture?

Where do we put our attention when we look at a building? 

How do we look at architecture?

Here's a photograph of a Civil-War-era field hospital with an eye-tracking heat map overlaid. It shows that observers pay the most attention (red and yellow areas) to direct human presence.

There's a figure standing in the doorway, and a group of other figures to the left. The interest in the upper windows appears to be a search strategy for finding other people, or at least for learning about human presence indirectly. No one looks at the ground, the trees, or the chimney.

How do we look at architecture?

What if no people appear in the photograph? How do we respond to the purely abstract elements of architecture on their own terms? Here are two photos of a building, one with the side windows removed by Photoshop.

Researchers Ann Sussman and Janice Ward have discovered from such studies that "People ignore blank facades. People don’t tend to look at big blank things, or featureless facades, or architecture with four-sides of repetitive glass."

How do we look at architecture?

They also observed that "buildings with punched windows or symmetrical areas of high contrast perennially caught the eye, and those without, did not."
Eye tracking of Civil War photos
Here's What You Can Learn About Architecture from Tracking People's Eye Movements

Do your eyes play tricks on you?

Do you see things exactly as they are, or do your eyes play tricks on you? Check this diagram:

Do your eyes play tricks on you?

Are the horizontal blue bands tilting up or down? Are they straight or do they twist and bend? Or are they straight and level?

If you hold something straight up to the diagram, you can verify that the blue bands are actually straight and level.

This optical illusion by Victoria Skye is a variation on the famous "Café Wall Illusion," in which rows of black and white tiles are slightly offset to the right and left to create a strange tilting effect.

Do your eyes play tricks on you?

Optical illusions remind us that our eyes — really our brains — do indeed deceive us. That's why we need to use the methods of checking lengths and slopes if we want to achieve accuracy in our drawing. 
Read more
Previous post (2009) on the Cafe Wall illusion
An interactive version of the Café Wall illusion with sliders that lets you change parameters
Pop Culture Cafe about the Skye illusion
Explanation of the illusion by Richard Gregory
PhosphenesChromostereopsis What is the complement of blue?'Facephenes': Hallucinations of faces, stimulated in the labArt is a record of selective attentionMaking a Hollow-Mask IllusionWhat does eyetracking tell us about the rules of composition?How do we look at architecture?Floor Tile Optical IllusionDo your eyes play tricks on you?

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