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Gurney Journey | category: Visual Perception | (page 2 of 15)

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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.

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Sensor Fusion Problem

One of the mysteries of visual perception is how the information all binds together into a singular experience after raw sensory data is decoded. 

Light enters our retinas, and the optic nerve feeds information back to the visual cortex. After that, the signal follows neural pathways to various areas scattered throughout the brain.

Sensor Fusion Problem

For example, the dorsal stream interprets movement, while the ventral stream decodes information about shape, color and object recognitions.

In addition to the visual streams, other streams of sensory information arrive via sound and touch. Those signal pathways also appear distributed around the brain. 

For a long time, neuroscientists supposed that all the various streams of sensory impulses must converge or fuse together at a central location, but it doesn't happen that way. 

Given the scattered nature of that neuronal activity, how is it that we feel that our perception is a single experience? 

According to neuroscientist Jeff Hawley's new conceptual model of the brain, the various areas in the cortex arrive at a preliminary conclusion of what they're looking at. They appear to form a consensus in a manner very much like voting. To do that they don't need to be in the same place.

Sensor Fusion ProblemRead More:

Sensor Fusion on Wikipedia

A Thousand Brains: A New Theory of Intelligence by Jeff Hawkins

NOTE: If you get my blog posts by email, you should know that Google is taking away email subscriptions next month. I'm trying to figure out a way to replace Feedburner for getting you your daily feed. Otherwise, you'll just have to click over to the blog to see new posts.

Seeing Depth for the First Time

Seeing Depth for the First Time

Neurobiologist Susan R. Barry was an adult when she acquired depth perception for the first time.

"Barry had been cross-eyed and stereoblind since early infancy. After half a century of perceiving her surroundings as flat and compressed, on that day she saw the city of Manhattan in stereo depth for first time in her life. As a neuroscientist, she understood just how extraordinary this transformation was, not only for herself but for the scientific understanding of the human brain. Scientists have long believed that the brain is malleable only during a "critical period" in early childhood. According to this theory, Barry's brain had organized itself when she was a baby to avoid double vision - and there was no way to rewire it as an adult. But Barry found an optometrist who prescribed a little-known program of vision therapy; after intensive training, Barry was ultimately able to accomplish what other scientists and even she herself had once considered impossible."

The story shows not only that the brain is malleable, but also that a conscious awareness of experience isn't the same as actually having that experience. As author Bruce Goldstein puts it, "Scientific knowledge is not enough." 

Seeing Depth for the First Time
Susan Barry tells her story in her book Fixing My Gaze: A Scientist's Journey Into Seeing in Three Dimensions

Are Artists Right-Brained?

There's a lot of information online about the difference between the two hemispheres of the brain and what that means for artists.

Many commentators suggest that each of us is either a "left hemisphere person" or a "right hemisphere person," as if we think and act primarily with one dominant hemisphere. This idea originated from studies in the 1960s and '70s with patients whose two hemispheres had to be separated by cutting through the connecting nerve bundle called the corpus callosum.

The notion that has percolated through popular culture is that each half of the brain functions separately.

Recent studies reveal that the truth is actually more nuanced than that.

Iain McGilchrist, a psychologist who has investigated this topic, suggests that different hemispheres of the brain are actually engaged in similar cognitive tasks, but each half approaches that task in a different way.

The right half focuses more on the big picture, and the left hemisphere focuses more on the details. The right brain appreciates metaphor, poetry, humor, and music, while the left brain is more focused on the notes, the denotive facts, and the logical conclusions. 

Although they have somewhat different styles of information processing, the two hemispheres are both engaged as you navigate through most tasks, and they work together when you're creating a painting. 

In this YouTube video, which is illustrated by a whiteboard animation, Iain McGilchrist explains the lateralized brain, and how that affects our personal and cultural styles of thought. 

 


The art teacher most strongly associated with this line of scientific reasoning is Betty Edwards, who wrote Drawing on the Right Side of the Brain and has updated it with a 4th Edition

Visual Form Agnosia

Visual form agnosia is the inability to recognize familiar objects. The problem isn't just being able to name something that you see; it's understanding the meaning of them, recognizing what they are.

Visual Form Agnosia

Roses from my video Flower Painting in the Wild

A person with such a condition might look at a bunch of roses and say it's "a cluster of convoluted pink forms held up by vertical green attachments."

People with visual form agnosia typically have otherwise normal eyesight, intelligence, memory, attention, and language ability. 

Visual Form Agnosia
Dorsal and ventral streams. Image from Slideshare

Scientists have studied patients with this condition, often caused by a brain injury. These studies have yielded insight about the localization of functions in the brain and the pathways followed by neural activity as images are decoded. Recognition of objects seems to happen in the sides of the brain, not along the top of the brain.

That led me to wonder if there's a resemblance between visual form agnosia and the particular mode an artist shifts into while doing a painting. That is, don't we have to shut off the "naming engine" or the "categorization machine" in order to really see what we're painting? 

Perhaps one day scientists will study what happens in an artist's brain at various stages of the process of drawing and painting. 

Three Stages of Vision

Vision doesn't occur passively. It's active, constructive, and largely unconscious.

And it doesn't happen all at once. Sometimes it takes a half second to process an image, and sometimes it takes a second or two. 

The light entering our eyes is translated and organized in stages, beginning with simple visual elements and proceeding to higher levels of interpretation. These stages of image processing start in the retina and continue in different parts of the brain.

Three Stages of Vision

For us to be able to see the flying white horses, our brain must segment the image and relegate the dark red shapes to the background, rather than vice versa. 

This kind of sorting normally happens unconsciously, but it's easy to intentionally flip the one set of horses from figure to ground and back again. 

Identifying the figure as a mythological flying horse and the whole pattern as a piece of art by M.C. Escher is the final and most sophisticated stage in image processing, involving several areas of the brain.

Eric R. Kandel et al., authors of a textbook on the Principles of Neural Science, describe the process this way:

Three Stages of Vision
"The brain analyzes a visual scene at three levels: low, intermediate, and high. At the lowest level, visual attributes such as local contrast, orientation, color, and movement are discriminated. The intermediate level involves analysis of the layout of scenes and of surface properties, parsing the visual image into surfaces and global contours, and distinguishing foreground from background. The highest level involves object recognition. Once a scene has been parsed by the brain and objects recognized, the objects can be matched with memories of shapes and their associated meanings."

Book: Principles of Neural Science by E.R. Kandel, et al.

Do You See the Face?

When you look at this shape, what do you see? 

Do You See the Face?

An animal or a person in a costume, or just an abstract shape? 

If you flip the shape over, another reading emerges...... 

Do You See the Face?

....and most people will see a face in profile looking to the left. 

This shape is called the Mooney Face, and it's used to test if special areas of the brain are activated for face recognition tasks. Indeed, the fusiform face area (FFA) lights up when you recognize the second diagram as a face. 

Previous post "Mooney Faces" shows additional examples





Research Gate

Are You a Super-Recognizer?

Are You a Super-Recognizer?

In this 10 minute podcast, cognitive psychologist Dr. James Dunn talks about "super recognizers." These individuals have an extraordinary ability to recognize individuals, even in cases where the encounter was very brief and many years earlier. 

Super recognizers are also adept at correctly identifying someone whose face may be partially disguised by a face mask or a hat or a new hairstyle. The ability is the opposite of prosopagnosia, the neurological condition better known as face blindness.

Dr. Dunn has developed a face recognition test to be able to find these super recognizers so that he can study them further at the University of New South Wales in Australia. At the website SuperRecognisers, there's a face recognition test that you can test your own ability. I got a 10 out of 14, which was OK, not bad, but not great.

Why Dogs Don't Like TV

Why Dogs Don't Like TVDog vision is different from human vision in several ways. They can't distinguish red and green.

And they don't have sharp focus in a central area of the retina. Instead of concentrating photoreceptors in the fovea centralis, which gives us humans very detailed and color-sensitive vision in the pinpoint center of our attention, they have a broader area of focus.

Dog vision may not be as sharp or as colorful as ours, but it's better at tracking fast-moving objects, because their eyes are optimized to respond quickly. 

Our photoreceptors have to recharge at a rate of about 60 times per second. This "flicker fusion" threshold is the recharge rate that allows us to perceive a steady image on a flickering source like a TV screen.

Watching video that refreshes at 30 or 25 frames per second will pass for stable reality for us—but not for a dog. As dog expert Alexandra Horowitz says, "Dogs have a higher flicker-fusion rate than humans do: seventy or even eighty cycles per second. This provides an indication why dogs have not taken up a particular foible of persons: our constant gawking at the television screen," which is not fast enough for dog vision. "They see the individual frames and the dark space between them too, as though stroboscopically. This—and the lack of concurrent odors wafting out of the television to engage them. It doesn't look real."

Their fast flicker-fusion rate and reaction time also explains why dogs are so good at catching flying frisbees or tossed chunks of cheese.
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From the book: Inside of a Dog: What Dogs See, Smell, and Know by Alexandra Horowitz

Can We Reconstruct Vision from Brain Activity Alone?

Scientists have scanned the visual brain while a person is looking at something to figure out if there were recognizable patterns in the brain that corresponded to the image the subject was looking at.


Researchers then took information from the scan feed and input into an image generating network (Deep Neural Network) that went through a series of iterations to match the inputs coming from the brain. (Link to YouTube) The resulting video of the evolving iterations is paired with the original target image.

The flickering, abstract video seems to put special weight on symmetry, heads, and eyes.

Sending fire from our eyes

We take it for granted that we see by means of light entering our eyes. The chain of effects begins when a source emanates light energy, which interacts with the surfaces of objects and then travels in all directions, some of it finally entering our eyes and activating our retinal receptors. The signals travel on to our brain, which decodes the information coming from those energized receptors. 

Sending fire from our eyes
The replicants in Blade Runner seemed to have light emanating from their eyes.
The effect was created with a light shining on a half-silvered mirror set at
45 degrees to the axis of the camera.

People haven't always imagined that vision works that way. Greek writers proposed that we see by means of a kind of fire that is emitted from the eyes toward the object. That idea, known as "emission theory" was bolstered by the reflective retinas of cats and other mammals at night. Other Greek writers doubted that notion. How could we see faraway stars at night? Could it be instead that all objects constantly emit a stream of particles? 

It took centuries to arrive at our modern concept of the eye as a organ receptive to bouncing beams of light. But the story doesn't end there, because vision turns out to be much more active and top-down than we thought. 

The eye is much more than a passive camera. A poet might say that a kind of fire comes from our mind and it meets the light at the front door of our eyes. The stream of data coming from our receptors is really very limited and fragmentary, and our minds have a very active role in fleshing out that trickle of information.

In the 1800s, German physicist Hermann von Helmholtz proposed the idea of "unconscious inference." The idea is that we receive incomplete information and the brain makes unconscious assumptions from this partial data based on previous experience.

As brain scientist Robin Carhart-Harris puts it: "We house internal models constructed by the brain rather than perceiving huge volumes of unfiltered raw information. "So much of our experience of the world is the product of our brain's internal predictive models rather than some kind of receptivity of information coming in." 
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Wikipedia on Emissions Theory

Sensor Fusion ProblemSeeing Depth for the First TimeAre Artists Right-Brained?Visual Form AgnosiaThree Stages of VisionDo You See the Face?Are You a Super-Recognizer?Why Dogs Don't Like TVCan We Reconstruct Vision from Brain Activity Alone?Sending fire from our eyes

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