Thursday, January 18, 2007

I see men, but they look like trees, walking

And he took the blind man by the hand and led him out of the village, and when he had spit on his eyes and laid his hands on him, he asked him, "Do you see anything?" And he looked up and said, "I see men, but they look like trees, walking." Then Jesus laid his hands on his eyes again; and he opened his eyes, his sight was restored, and he saw everything clearly.
--- Mark 8:23-25

I'm trying a new concept: planning the end to a series before I start it. Because I want to break the blog, this post is very long and boring, and is the first of seven such snoozers. Actually the rest should be a little shorter. The topic is Light. Future titles are:
  • Waves and Spectra
  • Emitting & Reflecting
  • The light shines in the darkness, and the darkness has not overcome it.
  • Genesis Cosmology: Let there be Light
  • The Light of the World
  • Why Light?
Today we talk about kinds of sight. Starting at the top, we have 20/20 vision. Can't get any better than that. Next.

A man with nearsighted vision can not see detail in things far away. I am such a man. I am woefully nearsighted (20/240). But don’t be deceived. It’s not that I cannot see things far away; I can see everything that you can, but it’s just not in focus. I merely can’t pick out all the detail that you can. Nearsighted people learn to adapt. For example, if I know your gait, I can tell it’s you walking towards me while you’re still 50 metres away, even though you appear as nothing but a pulsing blob.

In case you think that nearsightedness is purely a curse, please allow me to demisinform you. The full scope of creation’s beauty cannot be experienced by the 20/20 crowd. You might say that the trees get in the way of the forest. I was never so awed by the wonder of the night sky as the time I took a walk on a cloudless night without my glasses. Every single one of the visible stars had diffused into boggling auras and the Milky Way jumped out clear as day. Now I frequently walk without my glasses on my face. I still keep them in my pocket, because I might need to whip them on to avoid deadly peril, and I only walk without them when I’m alone, because it looks kind of idiotic when I walk into dangling tree branches or trip over small children.

Another bonus of my nearsightedness is the ability to use the thickness near the sides of my glasses as spectrum analyzers. If I hold a straight edge against a white background and cock my head just right my coke-bottle glasses act as prisms and I can tell you the primary colour composition of the straight edge. Well, it’s exciting to me.

A man with farsighted vision cannot see things in detail when they are right in front of him. We are all farsighted to a degree, because we cannot focus on objects that are a mere millimetre in front of our eyes. Another benefit of my own nearsightedness is that my eyes are able to focus on objects closer than an inch to my eye. I’m very much better at closeup sight than your average 20/20 guy.

At least, I used to be better. The magic age of forty triggered some new ocular developments. I am now acquiring the coveted farsightedness that is common for adults of a particular age. I just tried it out, and I can no longer focus on objects closer than four inches. Combine that with my nearsighted inability to focus on items farther away than six inches, and you come up with quite a limited range of clear sight. I’ve got my regular glasses, I’ve got my end of the nose reading glasses, I’ve got my full power bug-eyed reading glasses, and I’ve got my contact lenses, but I refuse to get bifocals just yet.

St├ęphane Dion has colourblind vision. A colourblind man cannot see all the colours that most people experience. But that statement is somewhat parochial. Let’s back up.

A blind mole rat is -- surprise, blind! It sees no light whatsoever. The blind mole rate is also extremely colourblind, because it sees no colours.

A dog has two kinds of cones in its retina. Two kinds of cones are simply not enough to see all the vibrant colours that we see. It sees in what we can best describe as shades of grey. Does my beagle really see in shades of grey? Probably not, but it doesn’t see any difference between red and green, or between red and blue, other than that they show up as different shades of the same colour. But between raids on the garbage can my beagle would scoff at you for saying she only sees one colour. You see, she has no access to your world, no access to the palette that you see. She thinks she sees lots of colours, but she has no idea what she’s missing.

A human being has three kinds of cones in its retina. We see all the colours of the rainbow. But you know what, if that is a true statement, then it is also true for my beagle. She sees all the colours of the rainbow that she can see, in the terms that she sees them, just as we do. Just like the beagle, we only see all the colours of the rainbow that we can see. But there are more colours in the bow of the Lord that we cannot see.

What human beings do see is the spectrum of colours from deep violet to warm red. We can see pretty comprehensively within that rang. Some humans are more sensitive to different shades than others, but most of us can distinguish thousands of hues and shades between violet and red. What we see is known as visible light, which is a circular definition if there ever was one.

Back to human colourblindness… A colourblind human being lives with a defect in one or more of their three kinds of rods, or they are actually missing a kind. The most common type of colourblindness involves an inability to distinguish between red and green. I have a friend like that. We and our kids were playing team lasertag once and the colours of the two teams were red and green. If you’re on the red team your gun flashed with red lights, and vice versa for green. My friend was helpless. He couldn’t tell friend from foe. He had to back himself into a corner and ask my father-in-law to point out the enemies to him. I think my father-in-law may have fingered me out more than my fair share, but that’s not a useful digression at this time.

What does my friend see? What is his vision like? I don’t know. I can’t crawl into his mind’s eye, and for his part he can’t even conceive of the splendour that my vision encompasses. Neither can St├ęphane Dion. Stephane Dion is kind of like my beagle.

Like the mole rat, a completely blind man cannot see a thing. I really wonder what he sees in his mind’s eye? How does he “visualize” the world? I would love to find out, especially if he has never experienced sight. Just like I have adapted to my nearsightedness, the completely blind man would also adapt. Probably the better question to ask would be: What do his mind’s ear, nose, and fingertips have that mine inevitably don’t?

Buy hey, a completely blind man can see at least two colours that I cannot see with my eyes. He sees with his skin. He sees infrared when his skin warms up as he steps into the sunlight. He sees an an infrared silhouette when someone passes between him and a radiant fireplace. He also sees ultraviolet when his skin “burns” as he sits under the sunlight. I grant that this particular ultraviolet detection system isn’t very useful, because his brain doesn’t actually "see" the ultraviolet until he feels the burn, which might not be until long after he left the sunlight.

Okay now, all you young 20/20 vibrant colour seers. You’re feeling pretty special right now. You’ve got 120 million rods in each eye to detect light intensity. You’ve got several million cones in each eye to detect colour, and you have all three types of cone, so you are not colourblind.

I’m afraid you are colourblind, every last one of you.

Birds were created with four types of cones. Where we experience a vibrantly hued world granulated by cones that allow our brains to triangulate the entire visible light spectrum by detecting three different frequencies of light, the fowl of the air have a fourth cone calibrated to detect ultraviolet frequencies.

So what? Birds can see a little bit more of the rainbow that we can. Well it’s very much more than that.

Imagine that you woke up tomorrow to find that you really lived in a four dimensional world, and that the three dimensions you’ve always known were only part of the story. Can you imagine it? It’s difficult to do. We can describe it mathematically, but we can’t grasp it in our being. The comparison between our vision and bird vision is analogous.

The eagles don’t just see a little bit more of the rainbow. They detect the ultraviolet hues that are all around them in every object. They see things that we just can’t see, but are nonetheless very real. They don’t triangulate colours, they quadrangulate them. They add another colour dimension. Just as the world I perceive is exponentially more vibrant than my beagle’s, and just as my laser tag friend can’t conceive of a world of full colour, I can’t imagine what the sparrow sees, and my heretofore rich vision is orders of magnitude more beggarly than the tern’s.

I do not see the fullness of the Light around me to any appreciable degree more than my beagle does. But you want to know a secret? Neither does the hawk.

That's all for today, class. Everyone please wake up and go home now.


Anonymous said...

Did someone say vision?

Wrymouth said...

Neat. Didn't know about bird vision, although I did know some insects see ultraviolet.

Look for white flowers on plants. Didja know some of them aren't white in color -- they are ultraviolet?