What You See is Different Than What You Look At

The physiology of vision

Despite common belief, humans do not perceive a direct and exact representation of external physical reality, but a distorted translation formed by their eyes and brain. The image we see is different than what we are looking at. This is not some coffee house theory, but a physiological fact. The human eyes and brain do a decent but imperfect job at detecting and translating light.

This post is a look at the physiology of seeing and offers examples of optical distortion caused by the eyes and brain.

A quick look at the physiology of seeing

When a human looks at an object, light from the object enters the eyes. The light goes through the cornea, which is a clear covering, then through the pupil which is a clear circle in the center of the colored part of the eye called the iris. The pupil gets larger (dilates) when there is little light and smaller when there is more light. The lens focuses the light through the aqueous humor, a clear liquid, onto the retina. The retina, in the back of the eye, contains millions of tiny photosensors that detect the light. There are two main kinds of photo sensors, called rods and cones. Shaped like rods, rods detect shades and forms and are needed for night and peripheral vision. Rods are not good at detecting color. Shaped like cones, cones are needed for seeing details, seeing in daylight and detecting colors. Cones do not work well in low light. Rods and cones cover the entire retina except for a spot where the optic nerve connects to the brain. The optic nerve carries the information received from the retina to the brain, where the brain translates it into the single image we perceive, or 'see.'

The Blind Spot

All humans have blind spots, which are spots where the eye cannot see. The blind spot corresponds to the spot on the retina where the optical nerve connects the retina to the brain. At this spot there are no light-detecting cells and, thus, it cannot detect light. A small object can disappear from view.

In everyday life, the blind spot goes unnoticed. This is in part as the eye is constantly looking around, getting a wide and varied range of views. It is also in part as the brain uses the information from both eyes to create a single mental vision. What one eye misses, the other often picks up.

As its optical nerve connects differently, the octopus has no blind spot.

Detecting your blind spot

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L                                   R

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To detect your blind spot using the just shown letters L and R, hold the screen about two feet in front of your face, close your right eye and look at the letter R. Don’t look at the L. Slowly move your head forward, towards the picture. At one point the L will disappear. The L will also disappear if you start up close and slowly move back. Notice that the missing spot is filled in white by your brain, so it appears as if nothing is missing from your view. This illustrates how your blind spot goes unnoticed during daily living. Many people live their entire lives not knowing they have a blind spot.

Humans have more glaring blind spots. Due to the placement of our eyes in our heads, we can't naturally see behind us, under our feet, from the top of our head, behind our elbows. If you want to sneak up on a person you approach from behind.

Other animals have different eye placements and fields of view. As a robin has its eyes on the side of its head, it has a better side view but worse directly ahead view. The robin's life depends on its being able to detect predators from the side and back. When hunting for worms in the grass, robins turn their heads. Some think they are turning their ear to listen for worms when they are turning their heads to see in front of them. A wolf, which is a hunter stalking prey, has eyes placement best suited for seeing ahead. The wolf sees better straight ahead, but its side-to-side vision is worse than a robin's. A crocodile has eyes that rise above the rest of its head. Not only does this create a different field of view, but allows the crocodile to see above water while most of its head and body are hidden below water.

After Images

Afterimages are when, after staring at an object, you look away and still see an image of the object. An example is when you still see the nighttime headlights of a car, even though your eyes have closed and the car has turned away. Another is when after looking away from a candle flame in the dark you still see light in the shape of the candle flame.

Stare at the red circle below for about ten seconds. When you then look at the right dot you will see a ghostly circle around it.

Afterimages happen after the retina's photosensors (the rods and cones in your eyes) become over-saturated, or burned out, from staring at a particular color. This burning out is comparable to lifting weights in the weight room. After doing enough arm curls you lose your arm curl strength for a short while and will be able to lift only lighter weights. Your muscles are fatigued, if only temporarily, from all that weight lifting.

Similarly, after staring at a large area of a single color, the eye’s photosensors lose their strength for that color. If right afterward the eyes look at a blank piece of paper, the photosensors will be weak towards the previously stared-at color but fresh and strong for detecting the other colors. This imbalance causes the brain to perceive the image (the afterimage), but in the color opposite to the original color. To the brain, the weakness towards one color means the presence of the opposite primary color is stronger. Quirky perhaps, but this is the way the brain works.

If you are staring at a green image, the afterimage should be red (the opposite primary color). After staring at a yellow image, the afterimage should be blue. The brain sees afterimages in primary colors, so any non-primary color (orange, pink, etc) will be seen as the primary opposite.

Though they occur almost constantly, afterimages usually go unnoticed. Afterimages are best observed when focusing on a single color or object for a lengthy period of time. In normal about the house viewing we view a wide range of objects and colors at once and our eyes are always moving around, the view constantly shifting. In these cases, the afterimages are minor and get lost in the visual shuffle. We barely if at all notice them.

Binocular Vision

Humans have binocular vision, meaning the single image we see in our brain is made from two different views-- one from each eye.

Binocular vision gives humans a number of advantages. One is we have a wider field of view than if we had only one eye. The right eye can see further to the right and the left eye further to the left. The single vision in our brain shows more than either single eye can see.

Another advantage is the two views give us imperfect but good depth perception. People who are blind in one eye have worse depth perception than the average human.

The mythical Cyclops might at first appear an unbeatable foe, but a wily human opponent could take advantage of the monster's poor depth perception and narrow field of vision.

Triangularism and Calculating Depth

Binocular vision produces the perception of depth, similar to how triangularism measures length in applied mathematics. When looking at a distant point using only one point of view it is hard to impossible to determine the distance accurately. In applied mathematics, triangularism can accurately calculate this distance from point a to point b by creating an imaginary triangle. Triangularism has long been used in the real world to measure distant objects, such as islands and boats from land and when surveying land.

Triangularism: From point a alone, it can be impossible to accurately calculate the distance to point b. In the real world, point a could be you standing on land and point b an anchored boat out at sea. However, by taking angle measurements from point a, then taking an angle measurement from nearby point c (perhaps a walking distance away), and measuring the distance from point a to c, one can create an imaginary triangle that calculates the distance from point a to point b. It’s just a matter of calculating angles and doing the math.

Two eyes give the brain a similar two-point view, and the brain uses these two views to judge distance. This is mostly done nonconsciously. You simply reach out and grab that pencil or door knob with no problem. If you wear an eye patch, you may discover it’s more difficult to grab things on the first try.

The Hole In The Hand Illusion

This simple trick plays with your binocular vision to make it appear as if you have a hole in your hand.

Roll a normal piece of 8x11" paper into a tube and place it next to your hand as shown in the above picture. With one eye look through the tube and with the other eye look ahead at the back of your hand. With a little bit of shifting, you should see what appears to be a large hole through your hand. Your brain takes the two distinct views to create one bizarre view.

Night versus day vision

Albert Ryder's The Race Track (Death on a Pale Horse)

Due to our optics, humans see better in daylight than dark. This is reflected in our perception and description of the world and in our art and language.

There almost always is light when it is pitch black to humans, but it is in wavelengths human eyes can’t detect. Ultraviolet and infrared light are always present but invisible to humans. A human can get a suntan from ultraviolet light and feel the warmth associated with infrared light, yet is unable to see either.

There are legitimate reasons for humans to naturally fear, or at least be wary, of the dark. We don't know what's out there. If we run in it, there's a good chance we could trip and fall. That's not superstitious, that's common sense.

Other animals have night and day vision different from humans. Owls see better in the night than in the day. It's not that objects such as picnic tables and fence posts physically vanish in the dark of night. It's that humans are unable to see them. Owls see them fine. Geese see ultraviolet light invisible to humans. Geese's eyes see all the color we see, plus the color of ultraviolet. Goldfish can see both ultraviolet and infrared light.

The goldfish is the only animal known to be able to see both ultraviolet and infrared light

Darkness is popularly associated with sinister, and light with goodness. Look at the common dark words and phrases:

She has a black heart

The darkness of his soul

He has a dark mind

Heart of Darkness

In Western culture, white, yellow and other bright colors are associated with happiness and goodness. Someone who is upbeat and smiley is said to be in a bright or sunny mood.

Hell is commonly pictured as shadowy and Heaven as sunny. Good angels are typically described as wearing white. Virginal brides wear white. The Wicked Witch of the West wore black. The Good Witch of the East wore white. Vampires, as the stories go, rise at night from their coffins and die when exposed to daylight. The cursed man becomes a werewolf at the full moon of the night.

Final Thoughts on Human Vision

As I wrote, you don't see physical reality even in the physical world, but a translation of it. As demonstrated, binocularism (changing two views into one), afterimages (images created by the eyes/brain), unnoticed blind spots, inability to see colors in low light and countless other purely physiological occurrences ensure that our mental image is always different than the objects viewed. Everything we perceive involves illusion.

• If you believe that there is a God who purposely created animals, why do you think he gave humans such limited eyesight?

• A mirror mirrors what is in front of it. If you place an apple two feet in front of the mirror, an identical-looking apple will look as if it is the same distance behind, or into, the mirror. Curiously, if you use triangulation to measure the distance to the apple in the mirror, the apple will measure as being two feet behind the mirror. Both our eyes and scientific measurements say there is an apple two feet behind the mirror's surface.

• Infrared viewers, such as night vision goggles, do not allow humans to see infrared light but translate infrared light into visible light. We cannot see infrared light and can only guess how an infrared-viewing animal perceives it.

• Have you ever noticed that when you’re outside at night, you can see a star better when you’re not looking straight at it? The center of your retina does not have rods which are used to see at night. The rods are off-center, so you see better at night off-center. When looking at a faint star, try turning your head a bit as it may appear brighter out of your periphery.

• Given humans’ night vision, it is no coincidence that humans perceive ghosts as things that come out at night, are pale and colorless, ephemeral, fleeting, peripheral, dreamlike, shimmering, mysterious, and otherworldly. Under the shroud of night a lawn chair can look like a shadowy figure. A backpack left on a picnic table can resemble a strange animal. As there is a lack of visual information at night, humans use their imaginations to fill in the story.

• While humans depend mostly on sight, other animals depend more on other senses. The bloodhound has worse than human eyesight but uses its advanced sense of smell to find lost people that even trained police detectives cannot find. In these instances, the bloodhound's non-seeing perception is more accurate than all of the detectives' senses combined. This explains why many police departments have bloodhounds on staff.

• Our perception and description of the universe are greatly influenced by our senses. Humans categorize and label objects in part by visible colors. Many animals, flowers, gems, and even humans are defined by their visible colors.

• As defined by the American Kennel Club, a cairn terrier can come in all colors except white. If a cairn terrier is born white, it’s not a cairn terrier. It’s a West Highland Terrier, a different breed.

• If we could see infrared and ultraviolet light our categorizations and objects, including terriers, would be different.

• If you said you believe that there is a God who purposely created animals, why do you think he gave some animals better eyesight than humans'?

• Considering, for example, we would have better depth perception and receive more information if we had more eyes, how would you design perfect eyesight? Realize that if we had one hundred eyes all over our body, we would still have limited perspective due to where we stand, our height, etc. What would be perfect eyesight? What about perfect perception? Our physical perception would still be limited if it was just about eyesight. Remember smell, hearing and other senses. How would you design perfect perception? Are there senses we don't use or know about? Also realize that such advanced perceptual systems would require a bigger, different brain to process and interpret the visual information, and the sensory information would still be interpreted and transformed by the brain.

• Do you think art is a way to make up for our limited senses? A great painting or movie doesn't just show something but implies and evokes. A great work of music is more than just physical notes.

• It's fascinating how much human philosophy, religion, and society are formed and influenced by human sensory abilities and disabilities.