Gurney Journey | category: Visual Perception | (page 1 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.

Bistable Percepts

Most people are familiar with the face / vase illusion (below). Psychologists refer to it as a "bistable percept." 

Bistable Percepts

A bistable percept is an image that can be perceived in two different ways. The perception can switch back and forth between the two interpretations, but you only see one at a time. 

Bistable Percepts
Another example of a bistable percept is the Necker cube which switches from appearing above you and projecting to the right, to appearing below you and projecting to the left.

One characteristic is that the duality, once perceived, can't be forgotten.

Ambiguous Images

Take a look at this picture. What do you see? When you look at it again, do you see something else?

Ambiguous Images
Image courtesy Steve Stuart Williams and Tim Urban

Most people see a man, off balance, running into a snowy forest. Then after looking again, they see a dog running toward us. Some people see the dog first and have a hard time seeing the human.

What's going on is that there are two opposite streams of information processing going on in your brain. One stream is like a camera. Light enters your eye and resolves into shapes and patterns that move to the back of the brain and up through the cerebral cortex to higher level processing. 

But while this is going on, the brain is constantly generating theories of what it's seeing and delivering those theories down the pipeline, optimizing what you're actually seeing to fit its dominant conception.

All along you're reality-checking the top-down theory against the information coming up the pipeline from the eyes.

If the first top-down reading doesn't continue to fit the bottom-up facts, you start generating new interpretations.

A similar process happens with auditory processing when you hear a gunshot...or was that a firecracker?...or was someone popping a paper bag? You can feel your adrenaline surge when you think it's a gunshot, and all that changes when you realize it isn't.

Weird Science of Visual Perception

This was a cover feature I proposed for ImagineFX Magazine . They never used it, but I still believe it would be an awesome subject for artists. 

Weird Science of Visual Perception

Birdman, oil. I used mainly four colors: viridian, permanent alizarin, yellow ochre, and cerulean.

Knowing about the science of eye-tracking, color vision, afterimages, and image processing helps us a lot as image-makers.

Read my previous posts on Visual Perception

The Role of Prediction in Perception

Stored Sunlight, 5 x 8 inches, watercolor and gouache

"The mind is a prediction engine, and nowhere is this more true than in visual perception." 

Comparison with photo taken after the fact

In his book "The Mind: Consciousness, Prediction, and the Brain," by E. Bruce Goldstein details current research about how the process of visual perception. 

What happens when we see is that the brain creates a top-down model of the world and continually checks it against the input coming from our senses.

"The mind encompasses everything we experience," he says, "and these experiences are created by the brain--often without our awareness. Experience is private; we can't know the minds of others. But we also don't know what is happening in our own minds."

This podcast interview with Goldstein lays out the issues well.

Attentional Spotlight

We bestow our visual attention very selectively, and that hierarchy of awareness is called the attentional (or foveal) spotlight. It's like exploring a pitch-black house at night with a narrow-beamed flashlight.

The fovea is the central spot of the retina, which is packed with photoreceptors, especially color receptors. In the peripheral retina there are fewer receptors, and they tend to be more responsive to tone and movement.

Attentional Spotlight
Robert Frederick Blum, Venetian Lacemakers, 1887, Cincinnati Museum

As I understand it, the attentional spotlight is more than just a structural feature of our photoreceptors. It also describes an aspect of our cognitive awareness of the world around us; some would say it's a central quality of consciousness itself. We focus our attention on elements of our world that match our conscious or unconscious search parameters, or distractions that pop up, competing for attention. 

Painters can capture the experience of the attentional spotlight, by helping the viewer know what's important, and downplaying the rest. It helps to darken, simplify, or blur areas that are less important. In the painting by Robert Blum, look at how much he downplays the peripheral areas in the foreground, and below the chairs, and keeps our attention within the circle of illuminated faces and hands.

Introduction to the attentional spotlight

Research Gate: Spotlight Model of Visual Attention 

Brain Scanners that Recognize What You Have Looked At.

In recent years, brain imaging studies have been able to recognize what image a person is looking at purely from brain activity. This is possible because the image maps onto the visual cortex almost like a blurry projection.

Brain Scanners that Recognize What You Have Looked At.
But now scientists have gone a step further. Researchers studying patterns of brain activity can correctly identify what image you have seen in the past, or even what image you're imagining, based on brain activity.

The research examines how you remember — and imagine— pictures that you've actually seen. It turns out that similar mechanisms come into play when you imagine something compared to how you process the real thing. 

The scanning system is still in its infancy, but it portends the kind of mind-reading device described by science fiction authors. "It's what you would actually use if you were going to build a functional brain-reading device," said Jack Gallant, a neuroscientist from the University of California, Berkeley.

CNN: Brain scans reveal what you've seen

Brain Inspired Podcast: Thomas Naselaris | Seeing vs. Imagining

How much data does the eye transmit?

Researchers estimate that the neural wiring from the retina transmits information to the brain at approximately the same rate as an Ethernet connection, about 10 million bits per second. That sounds like a lot, but it's not as much information as we think we're getting. 
How much data does the eye transmit?

"Much research on the basic science of vision asks what types of information the brain receives; this study instead asked how much. Using an intact retina from a guinea pig, the researchers recorded spikes of electrical impulses from ganglion cells using a miniature multi-electrode array. The investigators calculate that the human retina can transmit data at roughly 10 million bits per second."

"The retina is actually a piece of the brain that has grown into the eye and processes neural signals when it detects light. Ganglion cells carry information from the retina to the higher brain centers; other nerve cells within the retina perform the first stages of analysis of the visual world. The axons of the retinal ganglion cells, with the support of other types of cells, form the optic nerve and carry these signals to the brain."

As we've seen in previous posts, the impression we have of a highly detailed world don't come entirely from the eye, but also in a top-down fashion from in the form of predictive models from memory centers in the brain.

Read the article at Science Daily

A Funny Face

Have you seen this painting of Ada Lovelace, the Victorian lady who helped invent the computer? Her eyes are kind of close together, but you get the idea. The image was created by a computer.

A Funny Face
Image courtesy Daniel Russell @danielrussruss

Now look at the image again. Do you see a dog with a white nose? Ada's eyes become the nostrils.

I found that once I saw the dog, I couldn't go back to Ada Lovelace again.

A Funny Face
Most humans see the Victorian lady first. What does Google reverse image search think it is? Mostly it think's it's a dog, but there are some ladies mixed in, too. 

Pipeline of Meaning

Our eyes work with our brain to make sense of the world. 

At any given moment our conscious attention is fixated on one spot, but we're also guessing what's around it. This peripheral awareness cues the eyes where to jump next. That jumping or saltation happens about three times per second. 

By combining data from brain scans and eye-tracking, scientists at the University of Birmingham are trying to understand how we guess at what the next point of attention might be, and how different regions of the brain cooperate in this "pipeline of meaning" as "one object is established while another region of the brain is simultaneously deciding which next item is important."  

Pipeline of Meaning

N.C. Wyeth (1882-1945), The Studio, ca. 1913-1915, oil on canvas, 16 x 20 1/4 in.
Collection of Mr. and Mrs. Frank E. Fowler. Photo Rick Rhodes

The scientists say: "Humans do not necessarily perceive objects simply one after another (in series), and nor do they perceive items simultaneously (in parallel). Instead, they establish a pipeline of observations, in which meaning from one object is established while another region of the brain is simultaneously deciding which next item is important."

A similar process happens when we read text. "The neuronal activity required to scan the next word in a sentence also increases according to the complexity of the word."
Bistable PerceptsAmbiguous ImagesWeird Science of Visual PerceptionThe Role of Prediction in PerceptionAttentional SpotlightBrain Scanners that Recognize What You Have Looked At.Oscar Reutersvärd, Master of IllusionHow much data does the eye transmit?A Funny FacePipeline of Meaning

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