What reality are you creating for yourself?

There’s a story from the mid-20th century of an anthropologist studying pygmies in a jungle of Africa. He took one pygmy on a trip to the savanna. The pygmy had never been out of his jungle. He saw a herd of willdabeast in the distance and asked the anthropologist what type of insects they were – he had no practical frame of experience for understanding such distances. Our cultural or life experience can frame perception . A person who grows up in the plains will judge distances better but will misjudge the height of buildings and trees when compared to someone who grew up in woodlands.

What we perceive is a construct, in a very real sense, our minds create reality. For example, perspective is a illusion that we all accept on some level, even though we know that objects in the distance are not smaller (see blog cover photo).

Isaac Lidsky’s Ted Talk looks at how important vision is to us, how it constructs our sense of reality, an in his case, how it can be a sort of trap if you let it. His journey is about losing his site, and coming to the realization that he summed up in a statement by Helen Keller, “the only thing worse than being blind is having sight but no vision.”

Some interesting points from the talk about perception:

  • Hearing requires 2 – 3% of the brain’s processing capacity
  • Touch uses approximately 8%  of the brain’s capacity
  • The visual cortex takes up about 30 % of the brain’s capacity and processes as many as two billion pieces of information each second

But Lidsky explains that all information references “your conceptual understanding of the world” based on the context of your life, “knowledge, your memories, opinions, emotions,” etc. One example he gives …

“… what you see impacts how you feel, and the way you feel can literally change what you see … a hill appears steeper if you’ve just exercised, and a landmark appears farther away if you’re wearing a heavy backpack.”

Crash Course provides another overview of how perception comes together in the brain in Perceiving is Believing

Web Development Application
No direct application but it is helpful to know how demanding the visual cortex is. It also may be helpful to think about cultural (or emotional) frame of references when developing images and content for a Web page.

Related TEDTalk: Isaac Lidsky TED Talk

Post Script

TEDTalk by Anil Seth, "Your brain hallucinates your conscious reality"
According to neuroscientist Anil Seth, we're all hallucinating all the time; when we agree about our hallucinations, we call it "reality."

One interesting point of the Ted Talk is a section on introception – stimuli produced within an organism, especially in the gut and other internal organs.
Anil Seth TED Talk


The limits of vision

Our eyes can do amazing things, but we need to keep in mind that they can do nothing without the visual cortex, which takes up about 30 % of the brain’s capacity and processes as many as two billion pieces of information each second. It is the combination of sensor (the eye) and processor (the visual cortex) that create what we call vision. Let’s just list some of the capabilities of vision:

The earth surface curves (the horizon) out of sight at a distance of about 3.1 miles (5 km) but our vision can perceive far beyond the horizon. The farthest star we can see with our naked eye is V762 Cas (brightness magnitude 5.8 ) in Cassiopeia at 16.308 light-years distance (9.5868623^16 miles), but if the night is clear and you know where to look, you can see the Andromeda Galaxy (M31), that’s 2.537 million light-years away.

The shortest moment a person can see a light source is based on Bloch’s Law, which defines the visual threshold that is reached when both illumination and time reach a constant. Simply said, there’s a balance point between the intensity and duration in a flash of light. As extremely birth light might appear the same when shown for a nanosecond as a dim light shown for a tenth of a second.

One study shows that fighter pilots (people with very good eyesight) can observe an image flashed on a monitor for only 1/250th of a second. Most people can see a flickering light source as steady illumination at a rate of 50 to 60 times a second (or hertz).

The visual resolution of the human eye is about 1 arc minute (1/60 of a degree). At a distance of 20″, that’s about 170 dpi (pixels) – a dot pitch of around 0.14 mm. To translate this to something familiar, a 30″ monitor with a 16:9 aspect ratio would be sized around 26″ x 15″ and would need a resolution of 4400 x 2600 pixels to realize 170 dpi.

But there’s also angular resolution (the ability to distinguish two similar points that are close to each other). A simple example is car head lights, at a great distance they appear as one light, but at some point you are able to tell that there are two lights.

Angular resolution is measured in arc minutes (1/60th of a degree) and seconds (1/3600th of degree) of field of view. The angular resolution average human eye is one arc minute. For example, a one third of a millimeter wide line seen at arm’s length is 1 arc minute.

Foveal viewpoint
The fovea is the part of human eye responsible for sharp central vision (the only part of the retina that permits 100% visual acuity) The fovea is small, only about two degrees, and is necessary for visual detail like reading or tracking moving objects (hunting). Objects outside of the fovea are not in focus, even though our brains tell us they are.


Over the next few days I’ll concentrate solely on vision.

Web Development Application:

There are many applications for understanding vision. For example, it is important to keep the limits of the fovea in mind when writing because most readers scan before they read, and only see a limited amount of the page.

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Tracking moving objects

There’s an old magic trick call the vanishing ball in which the magician throws a ball into the air several times and on the last time it disappears in midair. Here’s an example:

In reality, the ball doesn’t disappear, the magician palms it on the last throw, but up to two thirds of people claim to see the ball move up, and then disappear, on the last throw. This illusion takes advantage of our brain science and expectation, and it’s based on a very old evolutionary strategy that can best be as a hunting adaptation.

Predicting the future
A bird flying 30 mph can travel 44 feet in one second. When we see that bird our eyes take about 1/10th of a second to process the information (for the light hitting the retina to travel along the optic nerve and then be processed by the visual cortex). During that tenth of a second the bird will travel 4.4 feet, so our vision is always a bit off reality, the actual position of the bird should be invisible to us, 4.4 feet further along its flight path than what we see. Yet a primitive hunter could throw a rock and hit that bird – that’s because our minds construct a reality to predict where the bird will be. We can thank our evolution as hunters for this type of vision/perception


Web Development Application
Our eyes evolved to scan the environment and process massive amounts of visual data – as much as two billion pieces of information each second – but that’s image information, not text, and we can’t turn our evolution off. Reading text is really not natural to us, and when we read our brains are still in a very old evolutionary hunting mode. The point: we don’t see as much as we believe we do – we construct much of reality (and reading) in our minds. It is essential to understand that when people read that they don’t read every word (eye scan studies bear this out. See example below), so we have to construct headlines and writing for scanners.


We experience reading as a smooth experience, but this eyescan shows our eyes actually stop on words (dots) and that’s the only time we see with sharp focus.

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Field of View

Field of view is the angular extent of what can be seen with the eye. Various animals have different visual fields. Predators generally have more forward facing with binocular oriented vision, whereas prey have side facing visual fields with greater range (for defensive vision). Eyes positioned on the sides of the head is common in prey species, and increases an animal’s total field of view, but it’s often at the expense of sharper binocular vision.

A deer’s field of view can reach 280 degrees, a Rabbit’s field of view can be 360 with just a small blind spot for a short distance behind their head, but with limited binocular vision. A cat has a 200 degree field of view, but with an amazing 140 degrees of binocular vision. Nature has evolved and found advantage in many variations.


Human’s have general static view of about 135 to 180 degrees horizontally, with about 120 degrees of binocular vision. Ho ever, with eyeball rotation (about 90 degrees) the field of view extends to 270 degrees. In addition, vertical field of vision for humans is about 50 degrees in the upper visual field and 70 degrees in the lower visual field.


Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the visual field that is included in the notion of peripheral vision.

In addition field of view is, in a way, limited by the fovea, the part of human eye responsible for sharp central vision (the only part of the retina that permits 100% visual acuity), which is only about two degrees of field. Our wide, 120 degree field of view for binocular vision is the basis for stereopsis and is important for depth perception, he remaining peripheral 60–70 degrees does not provide binocular vision.

Web Development Application

Currently the applying knowledge of field of view for Web development is only of minimal importance, understanding the limits of a foveal view is more important. But as our use and understanding of virtual technology increases, it will doubtless require a significant understanding of field of view.

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Shades of Gray

“There’s nothing worse than a sharp image or a fuzz concept.”
Ansel Adams

We perceive light with photoreceptor cells (a specialized type of neuron found in the retina). The best-known rods (for vision in low light) and cones (for detecting color). We think of ourselves as primarily seeing color, but we have 20 times more rods in our eyes than cones. Shades of gray are very important for our survival.

rodRods and cones are narrow cells that are extremely sensitive – they can be triggered by a single photon of light. Rods are distributed differently in the retina (the retina contains about 120 million rod cells and 6 million cone cells), but the chemical process they work by is similar to cone cells – light stimulates the cells, sends signals to the brain, and the brain interprets the signals. At very low light levels you perceive vision using only signals from the rod cells in your eyes.

There’s quite a bit of disagreement on how many shades of gray a human eye can see. Some sources suggest only about 30, others say 450 to 500.

Interestingly, there are no rods at the “center” of the retina (the point directly behind the lens). That’s the location of the fovea (or fovea centralis), which contains only cone cells. The fovea is also the region of the retina capable of producing the highest visual acuity or highest resolution.

Many animals have only rod cells in their eyes: for example, pinnipeds, cetaceans, and some monkeys, and some animals like the tawny owl have tremendous number of rods in their retina. Monochromacy (mono meaning one and chromo color) or “total color blindness” normal in many animals, but a disease state in human vision.

Here a list rod characteristics

  • Used for scotopic vision (vision under low light conditions)
  • Very light sensitive; sensitive to scattered light
  • Loss causes night blindness
  • Low visual acuity
  • Not present in fovea
  • Slow response to light, stimuli added over time
  • Have more pigment than cones, so can detect lower light levels
  • Stacks of membrane-enclosed disks are unattached to cell membrane directly
  • One type of photosensitive pigment
  • Confer achromatic vision – relating to, or denoting lenses that transmit light without separating it into constituent colors.

Blind Spot: There is such a thing as the blind spot. It’s the location where ganglion cell fibers are collected into the optic nerve and leave the eye. No photoreceptors are found at the blind spot, but as always, or mind uses the information it has to construct reality, and we are not ware that we can’t see in that area. See a blind spot illusion:

Web Development Application

Understanding how we perceive shades of gray is very important for designers and graphic artists. See the article below: Shades of Grey in Accessibility

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“Mere color, unspoiled by meaning, and unallied with definite form, can speak to the soul in a thousand different ways.”
Oscar Wilde

There are so many things to say about our color perception. For example, the Human eye is capable of seeing between 7 and 10 million colors. Question: why is that massive range of perception so important?

We can define color vision as the ability of our eyes and brain to distinguish objects based on the wavelengths (or frequencies) of the light they reflect, emit, or transmit. We can point out that the typical human eye is only capable of perceiving light at wavelengths between 390 and 750 nanometers (the “visible” spectrum for Humans), and that our perception of colors is a somewhat subjective process – we all see the same illuminated object or light source a bit differently.

cone_cellWe can delve into the neurological process of three types of cone cells in the retina (up to 7 million) gathering information about visible wavelengths of light that correspond to short-wavelength, medium-wavelength and long-wavelength (red, green, blue). We can even frame the definition of vision as the process of perceiving color:

“‘Vision,’ by common usage, suggest a process; but it is now known that it is built out of many processes, subdivided into at least 32 areas. Before they eye’s input gets to the cortex it goes through two vision systems. One sees motion, and the other color. They largely come together in the primary visual cortex. Nonetheless, the overall visual system continues to stream continues this division into higher areas of the cortex. Vision goes into what a stream that identifies things and into a where stream that locates their positions. And even this description is a gross simplification.” Sagan & Skoyles, Up From Dragons

But the perception of color is much more complex …

What we see as color is, in a sense, an absence of colors. White light from the sun hits an object – let’s say a blue object – and all of the color in the white light (the full spectrum) is absorbed by the object with the exception of blue (and perhaps ultra violet and infrared). The blue is reflected to our eyes. The cones in our retina are stimulated at a specific frequency and sent to our brains for interpretation. We see blue – unless, of course we’re color blind.

But all color is perceived in context, as explained in Neuroscientist, Dr. Beau Lotto’s TED Talk,

Dr. Lotto sums our experience up like this, “The light that falls on your eye (sensory information) is meaningless, because it could mean literally anything. … There’s no inherent meaning of information, it’s what we do with that information that matters.”
Dr. Lotto also provides an example of why we evolved to see colors – pure survival. The example he gives in his TED Talk involves seeing a predator in the jungle. But there are alternative hypotheses.

Theoretical neurobiologist Mark Changizi has speculated that the reason Humans see is because it gives us an advantage in sensing emotions or health on the skin of others. Other neuroscientists suggest that our ability to see many shades of green help us differentiate between and choose plants to eat versus avoid poisonous ones.

No matter how we see the world, there always seems to be another view (as followers of biocentrism might say). Here are just a few interesting facts that we know about color:

  • Color Blindness: Men have a higher chance of being color blind than women. 1 out of 12 as opposed to 1 out of 255. The most common type of color blindness is the disability to tell the difference between red and green.
  • Tetrachromats: About 1.36% of the world’s population (only women) have a fourth type of cone cell in their retinas, (resulting in Tetrachromacy) giving them true four-color vision allowing them to see more than 100 million colors.
  • Depression & Color: Research published by Dr. Emanuel Bubl demonstrates that the retinas of depressed patients were less sensitive to contrast – making colors appear duller.
  • Shades of green: Human cones in the eye are more sensitive to green frequencies than any other. Humans are omnivores, so that not only can differentiating between shades of green plant help us find edible plants and avoid poisonous ones.
  • Ultraviolet colors: The Human eye is capable of seeing ultraviolet when the lens is Removed – some people are born with Aphakia – the absence of the lens on the eye. The great impressionist painter Claude Monet developed cataracts in his old age and after struggling to paint (with his colors washed out) he decided to, at age 82, have the lens of his left eye completely removed – the operation allowed him to see familiar colors, but it also let him see, and paint in ultraviolet (colors we cannot see).

Water Lily Pond by Claude Mone – circa 1926 – includes ultraviolet colors

Web Development Application

Understanding color in for development can be very helpful, underestimating its importance can be crippling, for example, not understanding the limits of users with color blindness. The best bet for avoiding issues is to have a knowledgeable graphic artist on your team.

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Saccadic eye movements

A saccade (sakad′ik – French, twitch, jerk) is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction. Saccadic eye movements are extremely fast voluntary movements of the eyes, allowing them to accurately “refix” on an object in the visual field, and change retinal foci from one point to another. Some Saccadic eye movements can be involuntary.

Saccades are one of the fastest movements produced by the human body with peak angular speeds of the up to 900°/s. An unexpected stimulus can commence a saccade in about 200 milliseconds (ms), and last from about 20–200 ms, depending on their amplitude. 20–30 ms is typical movement for language reading.

We do not look at the world with fixed steadiness, although our brain tells us otherwise. Our eyes move around, locating interesting parts of the scene and building a mental map in three-dimensions. Our eyes saccade, or jerk/twitch quickly, stop, scan, and then move again. The fovea (the high-resolution portion of vision, 1-2 degrees of vision) is one of the main reasons for Saccadic eye movements – we must move our eyes to resolve objects in our minds.

Saccadic masking
One of the most interesting points about Saccadic eye movements involves what we don’t perceive as our eyes move. One would think that no information is passed through the optic nerve to the brain while the eyes move in saccade, that is at least our perception experience, but that’s not correct. Saccadic masking or saccadic suppression begins just before your eyes move and keeps us from experience a blurred or smeared image. You can experience the saccadic masking effect with a very simple experiment: look in a mirror, look at your left eye, then change your gaze to look at your right eye – you won’t perceive any movement of your eyes, which is evidence that the optic nerve has momentarily ceased transmitting or that the brain just refuses to process the transmission.

Spatial updating and Trans-saccadic perception
One of the continually amazing things about perception is that our brain often perceives information that isn’t there. Spatial updating occurs when you see an object just before a saccade, and allows you to “make another saccade back to that image, even if it is no longer visible.” The brain somehow “takes into account the intervening eye movement by temporarily recording a copy of the command for the eye movement” and compares it to the remembered target image.

Trans-saccadic memory is the process of retaining information across a saccade. Neurologist think that perceptual memory is updated during saccades so information gathered across fixations can be compared and produced, creating what researches believe is a type of visual working memory.

Saccadic Dysfunction
There are a series of disorders that can produce abnormal eye movements. One is Nystagmus (also known as “dancing eyes”) a condition of involuntary eye movement (side to side, up and down, and other) that may reduce or limit vision.

Web Development Application
The understanding of saccadic eye movements has had a remarkable impact on Web usability in the form of eye tracking studies. By employing technology that monitors eye movements that can pinpoint precisely where a user is looking on a page, usability testers can study and better understand how people interact with text or online documents.

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Gaze detection

Our perception is, more often that we might guess, framed by our brain’s immersion in social interaction. One such perception is “gaze detection,” i.e., that sense that someone is looking at you. This is sometimes known as the “Psychic Staring Effect” (or Scopaesthesia).


National Geographic’s photo of young Afghan refugee Sharbat Gula’s piercing gaze. Is she looking at you?

In 1898 Psychologist Edward B. Titchener wrote that a class of his students believed they could “feel” someone staring at them from behind, which would force them to turn around. Since then many have claimed that the Psychic Staring Effect is actually a psychic phenomenon, but that notion has been discredited many times. The reasons for gaze detection are much more interesting.

The evolutionary importance of gaze detection 
There are very good reasons for human’s to be hypersensitive to gaze detection. The ability to tell where someone is looking is a critical non-verbal communication that can keep us alive by providing the an early warning system of an impending attack – we are “hard-wired” to err on the side of caution. Gaze detection also serves as an important social survival tool, to help us determine if someone has interested in us. Gaze detection is followed by direct eye contact, which is one of the most powerful non-verbal signals we can tap: it can convey intimacy, trust, intimidation, and influence. Even infants gaze at their parents to get attention and secure social bonds. The evolution of gaze detection is then evident – it’s an essential survival tool.

Factors of the gaze detection system

  • Gaze detection is an indicator that our peripheral vision may provide more information to our brains than we are consciously aware.
  • Gaze detection may be triggered by head and body positions. Reading specific body language clues likely alerts our brain to pay closer attention to the eyes.
  • Brain imaging has shown that superior temporal sulcus brain cells are activated when we see that we are being stared at.
  • The gaze detection system is particularly accurate at a distance. Human eyes make it easier to distinguish the dark center from the rest of the visible (white) eyeball. This makes gaze detection accurate within just a few degrees – we can tell if someone is looking at us or over our shoulders.
  • Gaze detection leads to direct eye contact, which provides crucial and complex communication for survival and reproductive success.

Web applications
Only two possible uses come to mind:

  1. There may be some application for images in marketing through the Web – it’s difficult to get users to look at advertising photos, a direct gaze may help.
  2. Direct eye contact may prove powerful in virtual reality applications/games.

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