Ever since the invention of colour television humans have been aware of the wonderful spectrum of colours available in our world. Today we’re going to discover how we interpret colours and how cool our eyes are for doing all this stuff without even charging us.
How did the eye evolve?
The evolution of the eye is deceptively simple and will all deceptively simple things we’ll begin by having you imagine you’re a bacterium.
If you’re a light-sensitive single celled organism you can tell if you are in light or if you aren’t. Good on you. Way to exist, buddy.
But here comes your great, great grandchild making you look like a chump ‘cause she’s got two light-sensitive cells. That means not only does she know when she’s in light, but she can tell which direction light is coming from. Sure makes you look like a piece of shit.
With each new cell comes an increase in resolution until eventually, many generations later, you’ll have a series of cells set up in an arc shape. Why an arc? As it turns out, the arc shape is perfect for understanding which direction light is coming from. If light hits the top of your arc but not the bottom you know that light is coming from in front and underneath you, aiming up. Aren’t you a clever collection of cells?
This is of course a very simplified method of explaining the evolution of the eye. A more complex one might one day exist in its own blog post, time permitting.
Why do we see colours?
This is a cool bit of evolution.
What we refer to as the ‘visible spectrum’ only forms a tiny portion of the electromagnetic spectrum. (That is, about 400 nanometre wavelengths to 700 nanometre wavelengths). Despite how small this range is, the vast majority of organisms only see in this spectrum.
This is because like Jaws, Godzilla and James Bond at the beach in Casino Royale at some point we triumphantly emerged from the water.
You see, water blocks out all but two small segments of the electromagnetic spectrum, one of these being visible light. Then, when we emerged from the water there was no evolutionary pressure requiring us to adapt to being able to see the other wavelengths, so we didn’t.
Isn’t that cool?
How do we see colours?
To understand how we see colours we must first understand what exactly a photoreceptor is, what a photoreceptor does and whether or not a photoreceptor should be doing that thing.
Breaking it down, a photoreceptor is a type of neuron which can take in energy (in this case, light) and convert it into a biological signal that can be processed by your brain. We’re okay with that?
There are two kinds of photoreceptor cells in the human eye: rods and cones. This means you have all the fixings for a basic limbo competition all within your retina.
Rod cells are almost entirely responsible for night vision, giving them a cool Splinter Cell edge. They’re cylindrical in shape and located on the outer edges of your retina. Go on, take one out and have a look. I’ll wait.
Rod Cells are the most sensitive form of photoreceptor cells. In 1998 D.A. Baylor discovered that rod cells will respond even to a single photon of light. Rod cells are sensitive enough that they really ‘get’ the music of Elliot Smith.
However, rod cells are not responsible for colour. In fact, rod cells only see in black and white. You can try this out for yourself. Next time the moon’s out and there’s only dim light have a look around and pay attention to what you’re seeing. You will only see in black and white.
Colour comes from the other type of photoreceptor cell, the cone cell. Not to be confused with the Coneheads.
On average you have about 4.5 million of these little Dan Ackroyds in your head. Cones aren’t nearly as sensitive to light as rod cones but they do allow for the perception of colours so don’t feel bad for them.
Dogs only have about 20% of the photoreceptive cones that humans have. This means that, while it isn’t true that dogs can only see in black and white, they actually see it in blue, yellow and grey. This means that Airbud simply would not be an effective team player as he’d have a difficult time discerning the hoop from the backboard and possibly even one team from the other. What an incorrect and excellent movie.
So, how do these dog enabling cones work?
Your brain contains three different cones, sexily named S, M and L. These cones are particularly sensitive to blue, green and red wavelengths of light. This is called trichromatic colour theory.
We can see how these light cones interact through this fun-time supergraph!
The incoming light strikes the cone-like portion of the cell, filtering the light with different wavelengths along different ‘response curves’. This allows for transmission of information such as wavelength and intensity which can then be interpreted by your pretty excellent brain.
And all of a sudden everything is absurdly colourful!
BONUS: So, what is blinking and why do we do that?
The specific purpose of blinking is to moisten the cornea. When your eyelids close, a salty secretion comes from your tear duct and moistens the exposed portion of the eye. Technically speaking, this is pretty gross.
But here’s the rub: You blink more often than necessary just to moisten the cornea
As discussed in an episode of Radiolab entitled Blink, some researchers are arguing that blinking can be considered a form of punctuation of thought. When processing information you tend to blink less, so when watching a film if there’s a pause on a shot of, say, an empty alleyway – you are more likely to blink in preparation of new information. The interesting part is – a significant portion of the movie theatre be blinking with you, all at the same time.
Imagine the sound that would make. Like an octopus stuck on a tiled floor. Never stop imagining that.
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