Sight

This is rambling article about human vision.

Blind spot
It all started when we were having fun with the “blind spot”. Its been known for ever that the blind spot exists. It is now well-known that is the position in the eye which has no receptor cells from where the optic nerve leaves for the brain.

I couldnt get it to work for it – but the wikipedia page worked perfectly for me. It was awesome !!!

http://en.wikipedia.org/wiki/Blind_spot_(vision)

Colourscolours

Colours have always been fasicnating. Aesthetically, scientifically. We know that there are basic colours – red, blue and green – from which all other colours can be derived. Changing the intensities of these colours and mixing them can produce virtually every other colour. And can be very entertaining too. It doesnt have to be exactly these three colours, but can be any three colours from three appropriate group. Why 3 ? It turns out, and it seems so obvious in retrospect, that there are three kinds of cone cells in the eyes. These cone cells are responsible for colour perception and their photoreceptors are of three kinds – most sensitive to red, geen and blue !

It turns out then – that night vision – vision in dim light – which is colourless – is due to biology again. Rod cells are responsible for this vision, as opposed to cone cells. And unlike cone cells they dont have the photopigment in them.

Some notable scientific greats have been intrigued with colour and have focussed their energies there.
Schrodinger, the genius who did many things, but is mostly known as one of the founding fathers of the quantum theory, and his quantum mechanical wave equation. He published a number of papers in the field of color, color perception and colorimetry.
While on the topic, it was Schrodinger’s book “What is Life?” that led to an entire generation turning their energies to research in that line that eventually led to the discovery of genes and established the field of genetics.

Maxwell, the Scottish giant, who consolidated the field of electromagnetics, and showed that light was an electromagnetci wave. He also contributed greatly to the kinetic theory of gases. Maxwell-Boltzmann distribution comes to mind.
What is not so well-knoown is that he made the first colour photograph. Roughly, he photographed the subject thrice, through 3 colour films. Then he projected the 3 images through the same filters again as a superposition to get a single image. It was in colour.

Perception

sight-Impossible staircaseSight is not only about colours. There’s a lot more to it apparently. A lot of software in the brain too. Perception, image recognition. It has been found that humans vision is espically wired for face recognition. But who knows ? If you look a bunch of monkeys or goats long enough, you can tell them apart eventually – even facially :)

One of the reasons we may have 2 eyes, it so that we can tell depth, or distance. Using the parallax effect. People with only one eye have a problem with distance estimation. The parallax effect is also using to estimate the distance of distant galactic objects. You can try it out locally for fun.

http://en.wikipedia.org/wiki/Parallax

The Eye

Our eye itself – our organ of sight – is a precious tool. With its key features – the cornea, the pupil, the iris, the lens, the retina – it pretty much resembles a camera. Of course, that’s the other way round. :)
When I consider that our eye is the original light capturing and image processing tool, I find it640px-Three_Internal_chambers_of_the_Eye quite amazing that its all made of cells. Living, biological cells. The lens – made of transparent cells. The cornea – with cells arranged in such a way as to focus and refract light. The retina with its millions of photoreceptor cells. The optic nerve acting as the cable that carries the image to our CPU – the magical brain.
Of course these are the cells in addition to the usual blood vessels, nerves and muscles.
The wonder of nature !

It is even more wondrous that ours is not the only kind of eye or sight. Many other creatures have different/better eyesight than ours.

Humans can see in the optical range, i.e. – 4000 to 7000 Angstrom.
Bees can also apparently see in the ultraviolet. So also many of those different flowers that look white to us humans, they are also reflecting light in the ultraviolet. That is a different colour for the bee, and they all seem a different colour to the bee.
Creatures of the cat family have a better night vision.
Bats are blind – but they can be said to have a radar/radio vision.
Snakes have a kind of infrared/thermal vision. Seems they can sense heat and make a image out of it.
Octopi have an eye that many researchers agree is more sophisticated than humans. Among other things, the nerve layout is on the behind rather than the front of the retina so there is no bling spot. Kind of inside out. Also their eye cells can regenerate – unlike humans.
Many insects, including bees again, have a “compound eye”. Among other things – this enables them to have a wider view, and in some cases they can also identify polarised light.
Amazing how people get to know all this stuff !

References / Further information

Feynman Lectures on Physics – Part 1
Wikipedia pages on Visual Perception, Human Eye, Compound Eye, James Clerk Maxwell, Erwin Schrödinger, Parallax, Blind spot.

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