Exploring a topic in depth
In this piece, we will take you through some of the interesting aspects of one of the most amazing powers of nature – the power of vision!
What would you look at if you had just three days of sight? Helen Keller, blind and deaf from infancy, writes in a remarkable essay, “I have often thought it would be a blessing if each human being were stricken blind for a few days at some time during his early adult life. Darkness would make him more appreciative of sight.”
The power of sight is an evolutionary miracle and yet the area of vision expands into territories that many of us have never crossed. Let us chart some of these miraculous and intriguing areas of our vision system.
How colour vision works
Open your eyes, and you are met with an array of different colours, but amazingly you can only detect three different wavelengths of light, corresponding to green, blue, and red. Combining these three signals in the brain creates millions of different shades.
Each eye has between 6 and 7 million cone cells, containing one of three colour-sensitive proteins known as opsins. When photons of light hit the opsins, they change shape, triggering a cascade that produces electrical signals, which in turn transmit the messages to the brain. Well over half of our cone cells respond to red light, around a third to green light, and just two per cent to blue light, giving us vision focused around the yellow-green region of the spectrum.
For instance, when you look at a banana, the wavelengths of reflected light determine what color you see (for a ripe banana, wavelengths of about 570 to 580 nanometers bounce back; the wavelengths of yellow light). The light waves reflect off the banana’s peel and hit the light-sensitive retina at the back of your eye. That’s where cones come in. When light from the banana hits the cones, it stimulates them to varying degrees. The resulting signal is zapped along the optic nerve to the visual cortex of the brain, which processes the information and returns with a color: yellow. For a visual detail, click here.
We are so used to seeing the world in red, green and blue that it might seem strange to think that most other animals cannot, but three-coloured vision like our own is relatively unusual. Some species of fish, reptiles and birds have four-colour vision, able to see red, green, blue and ultraviolet or infrared light, but during mammalian evolution, two of the four cone types were lost, leaving most modern mammals with dichromatic vision – seeing in shades of just yellow and blue.
This was not a problem for many early mammals, because they were largely nocturnal, and lived underground, where there was little need for good colour vision. However, when primates started moving into the trees, a gene duplication gave some species the ability to see red, providing a significant evolutionary advantage in picking out ripe red fruit against the green leaves.
Even today, not all primates can see in three colours; some have dichromatic vision, and many nocturnal monkeys only see in black and white. It is all down to environment; if you don’t need to see all of the colours in order to survive, then why waste energy making the pigments?
Watch this interesting Ted talk on how we see colors:
But do we see colors differently?
Well, strangely yes! Colour isn’t as objective as you might think though. Our brain decides what colour we are looking at based on the light that comes into our eyes, and there is actually a huge amount of variability in how we see colours. There are many ways colour can confuse our brains. How we see colour, however, is governed by much more than just our bodies. Our emotions, or even the time of year, can change how our eyes and brains interpret what we see.
For example, Yellow looks different to us depending on the season, according to scientists at the University of York. In the summer yellow appears more ‘greenish’ whereas in the winter yellow appears more ‘reddish’. This is the result of living in an environment where the level of green light increases in the summer. When the trees are full of leaves our eyes need to adapt. With extra green all around us, our brain has to recalibrate its understanding of yellow.
Researchers in Rochester, New York have found that feeling sad can impact on your ability to identify colours. Participants were shown swatches that had most, but not all, of the colour removed from them and were then asked to identify what colour they were looking at it.
A group who had watched the death of Mufasa in The Lion King found it harder to pick out blue and yellow than others who had not seen the film. Psychologists believe that dopamine – which controls our brain’s reward and pleasure centres – has an impact on how we distinguish these colours.
So while colour might seem to be one of the most straightforward things in our world, it is actually a mystery scientists are only just beginning to unravel.
To know more about how are our brains are tricked by colours, click here.
In many instances, other senses like smell, taste, sound and touch also have a bearing on our visual perception. For example, your visual perception of a pie shaped object may be confirmed, corrected or confused by the smell. You judge distance by sound-something is usually softer the further away it gets. In the dark, people typically feel about for walls, doors and tables. Echoes can fool you into misjudging location.
Seeing in three dimensions
Two Seeing Eyes = Two Views!
Two Eyes’ Views Used and Fused in the Brain = Stereovision!
What does it take to see life in 3D with depth perception…not to mention 3D movies or TV, virtual reality, 3-D stereograms, stereoscopic photographs, etc. etc.?
We are 3D creatures, living in a 3D world but our eyes can show us only two dimensions. The depth that we all think we can see is merely a trick that our brains have learned; a byproduct of evolution putting our eyes on the front of our faces. To prove this, close one eye and try to play tennis.
The miracle of our depth perception comes from our brain’s ability to put together two 2D images in such a way as to extrapolate depth. This is called stereoscopic vision.
Something to think about: Most predators have stereoscopic vision in order to gauge distance to their prey as they hunt. Most herbivores’ eyes are on the sides of their heads so that they can see as much of their environment as possible. They don’t see depth the way we do.
It works like this. Because your eyes are separated on your face, each retina produces a slightly different image. That difference in images is a direct result of the depth of the objects that we are looking at. Have you ever compared the different views of your right and left eye? The Eye Hop Game lets you do just that.
Each eye captures its own view and the two separate images are sent on to the brain for processing. When the two images arrive simultaneously in the back of the brain, they are united into one picture. The mind combines the two images by matching up the similarities and adding in the small differences. The small differences between the two images add up to a big difference in the final picture! The combined image is more than the sum of its parts. It is a three-dimensional stereo picture.
Stereoscopic vision works most effectively for distances up to 18 feet. Beyond this distance, your brain starts using relative size and motion to determine depth.
If you have any doubts about your equipment or your ability to see 3D, check out Why Some People Have Trouble Seeing 3D
This Is Just A Test — of Your Stereo Vision System
Are both your eyes turned on and working together as a team? Try this easy test and find out if you are a good candidate for 3D viewing. It’s The Framing Game and it only takes a minute!
If You’ve Got Stereo Vision, Count Your Blessings!
Here are just a few examples of general actions that depend heavily on stereo vision: throwing, catching or hitting a ball, driving and parking a car, planning and building a three-dimensional object, threading a needle and sewing, reaching out to shake someone’s hand, pouring into a container, stepping off a curb or step and many more of such everyday tasks and occupations.
To read more about the difference between the side vision of horses and other creatures versus the frontal vision of humans, check out an eye doctor’s in-depth explanation of how 3D stereovision and stereoscopic depth perception evolved in humans and other predator species (tigers, sharks, etc.)
These are some more interesting phenomenon of the eye- Blind spots, Afterimages, Natural delay in processing light, Hole in a hand illusion and Optical illusion, Floaters in the eye, Blue-field entopic phenomenon, etc. Click here for an amazing article that discusses some of these.
What is it crawling in my eye?
“Oh squiggly line in my eye fluid. I see you lurking there on the periphery of my vision.
But when I try to look at you, you scurry away. Are you shy, squiggly line?
Why only when I ignore you, do you return to the center of my eye?
Oh, squiggly line, it’s alright, you are in my eye.”
Did you ever feel like you have superpowers, that could see sky molecules, atoms, a magnetic force field in the sky or bacteria without the aid of a microscope – right in front of your eyes? Were you ever worried or terrified of having microbes or worms in your eyes? Or you thought you were going blind because you saw invisible sausages floating in your eyes? Or worst, your parents accused you of excessive smoking?
Well, these squiggly little things are what is called Floaters. Sometimes, against a uniform, bright background such as a clear sky or a blank computer screen, you might see things floating across your field of vision.
Watch this very illuminating video here to know more about these entities, residing right inside your eyes, yes inside your eyes, scary is it not? What are those floaty things in your eye? – Michael Mauser –