How The Brain Recognizes What The Eye Sees
- Salk Institute
- New work outlining the brain’s visual process could improve self-driving cars and point to therapies for sensory impairment, suggest investigators.
If you think self-driving cars can’t get here soon enough, you’re not alone. But programming computers to recognize objects is very technically challenging, especially since scientists don’t fully understand how our own brains do it.
Now, Salk Institute researchers have analyzed how neurons in a critical part of the brain, called V2, respond to natural scenes, providing a better understanding of vision processing. The work is described in Nature Communications on June 8, 2017.
“Understanding how the brain recognizes visual objects is important not only for the sake of vision, but also because it provides a window on how the brain works in general,” says Tatyana Sharpee, an associate professor in Salk’s Computational Neurobiology Laboratory and senior author of the paper. “Much of our brain is composed of a repeated computational unit, called a cortical column. In vision especially we can control inputs to the brain with exquisite precision, which makes it possible to quantitatively analyze how signals are transformed in the brain.”
“We applied our new statistical technique in order to figure out what features in the movie were causing V2 neurons to change their responses,” says Rowekamp. “Interestingly, we found that V2 neurons were responding to combinations of edges.”
Cortical Processing Of Visual Input
From the thalamus, visual input travels to the visual cortex, located at the rear of our brains. The visual cortex is one of the most-studied parts of the mammalian brain, and it is here that the elementary building blocks of our vision detection of contrast, colour and movement are combined to produce our rich and complete visual perception.
Most researchers believe that visual processing in the cortex occurs through two distinct ‘streams’ of information. One stream, sometimes called the What Pathway , is involved in recognising and identifying objects. The other stream, sometimes called the Where Pathway , concerns object movement and location, and so is important for visually guided behaviour.
How Do We See
Detailed diagram of the eye and its parts. Click for more detail.
Take a look around you. What do you see? You might see a computer or phone with a shining, colorful screen. A piece of paper may be under your left hand and a sharpened pencil in your right hand. While you look at these objects with your eyes, your brain is what is recognizing the objects. Many people take sight for granted, but how are you able to see and register objects?
You probably already know that your body has five senses that help you experience the world around you. These senses are touch, taste, hearing, smell, and sight. Although all of your senses are important, many people think that sight would be the most difficult one to live without.
If you could not see, how would you watch TV, cook food and not burn yourself, or walk across the street without being hit by a car? Many people do all kinds of activities without being able to see. Let’s learn a bit more about how vision works.
A comparison of a camera and an eye. Click for more detail.
The information that some animals receive through their eyes is called visual information or vision. For now, let’s think of the eye as a sort of camera.
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The Color System Of The Eye
Cone cells contain a pigment through which light must pass beforereaching the receptor. There are three pigments: One passes violet,with a wavelength of 430 nm one passes blue-green, with a wavelengthof 530 nm and the last pigment passes yellowish-green, with awavelength of 560 nm. In fact, these optical filters have filterskirts, meaning they pass light of other wavelengths, but with reducedsensitivity. Any monochromatic light actuallyactivates cone cells of multiple pigments, but at differentsensitivities. This also explains why we can see light with wavelengthsshorter than 430 nm, and longer than 560 nm.
No conecells, however, can truly perceive red. The closest we really get isyellowish-green. What we call red is really an opticalillusion, supplied by the brain by means of extrapolation. Oursensitivity to red is dramatically reduced compared to other colors,and our visual acuity in the red end of the spectrum is extremely bad.Everyone knows not to focus a projector using a redtest pattern. This is why the red gun in color-video equipment needsthe least resolution to be satisfactory .
Folk wisdom has many sayings about believing what you hear andbelieving what you see. The visual sense is just as prone to illusionas the auditory pathway, and equally filled with mystery andmisunderstanding. Maybe belief should rest not on the particularsensory pathway but rather on our understanding of the ways and meansthrough which we view the world.
A Range Of Neurological Vision Loss
- visual field defects such as homonymous hemianopia, when one half of the visual field in each eye is missing
- double vision where a single object is seen as two and cannot be merged together
- fluctuating vision this means the impairment is variable, for example, the person may be able to see something one day, but not the next
- visual acuity problems reduced clarity of vision
- eye movement problems for example, jittery eye movements or the tendency of the eyes to flicker around when the person is trying to look steadily at something
- strabismus the eyes are not aligned for example, it may turn inwards or outwards.
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What Visual Perception Tells Us About Mind And Brain
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Visual Processing Isnt All One Way
This bottom-to-top processing of our visual world may seem the logical path, but it isnt the whole story. Such a ‘bottom-up‘ approach would be far too slow and laborious, but more importantly, it would render our visual world full of ambiguity and we would struggle to survive. Instead, our perception relies to a very large extent on our previous experience and other ‘top-down‘ mechanisms such as attention. QBI Professors Jason Mattingley and Stephen Williams are both studying how attention can alter visual processing, using cognitive and cellular approaches, respectively.
As an example of top-down processing, consider the image below:
Wuhazet – Henryk ychowski
Square A looks lighter, but is actually darker than square B. Clearly, our visual system is doing a terrible job at seeing reality. But that isnt its purpose. Instead, our brains are trying to make sense of what they are seeing, rather than seeking the truth.
In the case of the above image, we automatically see based on past experience light and dark squares arranged in a checkerboard fashion, with a centrally lit portion and a shadow cast around the edges. With all of this information, we interpret A as a light square in shadow, and B as a brightly lit dark square. It isnt reality, but it is the most likely explanation given all of our previous experience and the data at hand. This is how our visual system works, ultimately to help us understand the world and so promote our survival.
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How The Brain Perceives Colors
Color vision is the ability to distinguish different wavelengths of electromagnetic radiation. Color vision relies on a brain perception mechanism that treats light with different wavelengths as different visual stimuli . Usual color insensitive photoreceptors only react to the presence or absence of light and do not distinguish between specific wavelengths.
We can argue that colors are not realâthey are âsynthesizedâ by our brain to distinguish light with different wavelengths. While rods give us the ability to detect the presence and intensity of light , specific detection of different wavelengths through independent channels gives our view of the world additional high resolution. For instance, red and green colors look like near identical shades of grey in black and white photos.
An animal with black and white vision alone wonât be able to make a distinction between, letâs say, a green and red apple, and wonât know which one tastes better before trying them both based on color. Evolutionary biologists believe that human ancestors developed color vision to facilitate the identification of ripe fruits, which would obviously provide an advantage in the competitive natural world.
What kind of colors do these animals see?
Skorupski P, Chittka L Photoreceptor Spectral Sensitivity in the Bumblebee, Bombus impatiens . PLoS ONE 5: e12049. doi: 10.1371/journal.pone.0012049
What Youll Learn To Do: Explain The Process Of Vision And How People See Color And Depth
Figure 1. Our eyes take in sensory information that helps us understand the world around us.
The visual system constructs a mental representation of the world around us. This contributes to our ability to successfully navigate through physical space and interact with important individuals and objects in our environments. This section will provide an overview of the basic anatomy and function of the visual system. In addition, youll explore our ability to perceive color and depth.
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Remembering What Is Seen And Visual Imagination
The act of copying information requires visual memory, as do a host of daily activities. The structures that serve this function include the hippocampi and the temporal and frontal lobes. The act of thinking about specific nouns leads to activity in structures within the inferior portion of the temporal lobes , along with frontal working memory areas. Active visual working memory is a function of the fusiform gyrus of the temporal lobe in association with the inferior frontal gyri. Ventrolateral areas are involved mainly in working memory for objects and dorsolateral areas are involved mainly in working memory for spatial locations. Recent experiments suggest that not only bottom-up signals from the retina but also top-down signals from the prefrontal cortex can trigger the retrieval of visual memories from the temporal lobes, which may serve as a neural basis for conscious recall.
Areas Of The Brain Affected By Stroke And Symptoms
Below, youll learn about the different parts of the brain that can be impacted by stroke. You will find a short summary of the effects of each type of stroke, and you can click the link in each section to learn more.
The effects of a stroke will vary from person to person, so its best to reference a full list of the secondary effects of stroke to get an even better idea of what to expect after stroke.
Here are the major areas of the brain that can be affectedby stroke:
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How The Eyes Communicate With The Brain
When we decide to look at something, a brainstem structure called the pons is called into action. It controls eye movement, constantly telling our eye muscles to move toward the correct stimulus of light .
When light enters the eye through the pupil, it strikes in the retina called rods and cones. Rod cells are responsible forperipheral vision and night vision, while cone cells react to brighter light, color and fine details.
When light hits its corresponding rod or cone, the cell activates, firing a nerve impulse through the optic nerve the middle man between the eye and the brain.
This impulse travels across countless nerve endings and eventually ends up with our pal the occipital lobe, where its processed and perceived as a visible image. This is eyesight.
Since an image isnt much help without meaning, the occipital lobe sends this visual information to the hippocampus in the temporal lobe. Here its stored as a memory.
All of this happens within the tiniest fraction of a second, allowing us to perceive the world in essentially real time.
The human brain is an incredibly complex web of neurons and synapses. And the more we understand about its mind-boggling ability to process and make sense of random collections of light, the more we can appreciate the equally complex world around us.
STILL HAVE QUESTIONS ABOUT YOUR BRAIN AND VISION? Talk to an eye doctor near you to schedule an appointment.
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The Dorsal And Ventral Streams
After the visual stimulus leaves the eyes, it is first processed through distinct points in the brain along the path to the occipital lobes. Then, that information exits the occipital lobes in white matter tract pathways called streams to other parts of the brain. The ventral stream is involved with object and visual identification and recognition. The dorsal stream is involved with processing the objects spatial location. In other words, the brain is figuring out what to do with the visual information it has received how to use it to recognize persons seen before map routes recognize symbols and letters and many other interpretations. These streams run through the temporal and parietal lobes, which is why sometimes surgery to these parts of the brain can affect visual processing as well.
The dorsal stream guides your actions and helps you recognize where objects are in space. Also known as the parietal stream , the where stream, or the how stream, this pathway stretches from the primary visual cortex in the occipital lobe forward into the parietal lobe. It is interconnected with the parallel ventral stream which runs downward from V1 into the temporal lobe.
The dorsal stream is primarily involved with the perception and interpretation of spatial relationships, accurate body image, and the learning of tasks involving coordination of the body in space. Damage or disruption to this stream can cause visual processing issues, including:
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Central Processing Of Visual Information
Vivid images of the world, with detail, colour, and meaning, impinge on human consciousness. Many people believe that humans simply see what is around them. However, internal images are the product of an extraordinary amount of processing, involving roughly half the cortex of the brain. This processing does not follow a simple unitary pathway. It is known both from electrical recordings and from the study of patients with localized brain damage that different parts of the cerebral cortex abstract different features of the image colour, depth, motion, and object identity all have modules of cortex devoted to them. What is less clear is how multiple processing modules assemble this information into a single image. It may be that there is no resynthesis, and what humans see is simply the product of the working of the whole visual brain.
Great progress has been made over the last century in understanding the ways that the eye and brain transduce and analyze the visual world. However, little is known about the relationship between the objective features of an image and an individuals subjective interpretation of the image. Scientists suspect that subjective experience is a product of the processing that occurs in the various brain modules contributing to the analysis of the image.
Occipital Lobe: Function Location And Structure
The Occipital Lobe helps with visual processing and mapping. It is located under the parietal lobe and above the temporal lobe near the back of the brain.
- Occipital Lobe
The occipital lobe is the seat of most of the brains visual cortex, allowing you not only to see and process stimuli from the external world, but also to assign meaning to and remember visual perceptions. Located just under the parietal lobe and above the temporal lobe, the occipital lobe is the brains smallest lobe, but its functions are indispensable.
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The Brain And The Eye
The eye works like a camera. The iris and the pupil control how much light to let into the back of the eye, much like the shutter of a camera. When it is very dark, our pupils get bigger, letting in more light when it is very bright our irises constrict, letting in very little light.
The lens of the eye, like the lens of a camera, helps us to focus. But just as a camera uses mirrors and other mechanical devices to focus, we rely on eyeglasses and contact lenses to help us to see more clearly.
The focus light rays are then directed to the back of the eye, on to the retina, which acts like the film in a camera. The cells in the retina absorb and convert the light to electrochemical impulses which are transferred along the optic nerve to the brain. The brain is instrumental in helping us see as it translates the image into something we can understand.
The eye may be small, but it is one of the most amazing parts of your body. To better understand it, it helps to understand the different parts and what they do.
ChoroidA layer with blood vessels that lines the back of the eye and is between the retina and the sclera .
Ciliary BodyThe muscle structure behind the iris, which focuses the lens.
CorneaThe very front of the eye that is clear to help focus light into the eye. Corrective laser surgery reshapes the cornea, changing the focus to increase sharpness and/or clarity.
FoveaThe center of the macula which provides the sharp vision.
ScleraThe white outer coating of the eyeball.
How The Eye Works
The sense organ for vision is an exquisitely evolved biological instrument for turning light into the brains language of electrical signals.
The eye is roughly spherical and about an inch in diameter. In the front, the cornea and lens focus light reflected from objects in theworld onto the retina in the back of the eye. The lens changes shape to allow us to see both near and far objects clearly.The retina contains nerve cells as well as a layer of 120 million rods and cones, receptor cells that respond to light. There are three kinds of cones, each tuned to different parts of the light spectrum. Some react primarily to red, some to green, some to blue light. Because of the brains ability to organize information about the relative intensity of these three primary colors-in essence, mixing them-from such a simple palette we can distinguish millions of colors.
The cones are most concentrated in the very center of the retinaa tiny spot called the fovea, responsible for our most acute vision and the region we use when we focus our vision on something.
Cones function well only in reasonably bright light. Rods, which are more than 100 times more light-sensitive, let us see in near darkness. But they dont distinguish colors, and so the twilight world fades to shades of gray. Similarly, because rods greatly outnumber cones in outer areas of the retina, colors seem washed out in peripheral vision.
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