Thursday, April 05, 2007

Tyger, Tyger Burning Bright….

Some comments over at the Growlery deserve some meandering in the blogsphere. First, the more one looks at the human eye (no pun intended) the more complex it gets. The eye may be the most sophisticated organ in the body including the brain. While we concentrated on the molecular events in the retina, maybe it is worthwhile to look at the overall structure for context:

From this site:
The retina is composed of 10 layers, from the outside (nearest the blood vessel enriched choroid) to the inside (nearest the gelatinous vitreous humor):

1. pigmented epithelium
2. photoreceptors; bacillary layer (outer and inner segments of cone and rod photoreceptors)
3. external (outer) limiting membrane
4. outer nuclear (cell bodies of cones and rods)
5. outer plexiform (cone and rod axons, horizontal cell dendrites, bipolar dendrites)
6. inner nuclear (nuclei of horizontal cells, bipolar cells, amacrine cells, and Müller cells)
7. inner plexiform (axons of bipolar cells and amacrine cells, dendrites of ganglion cells)
8. ganglion cells (nuclei of ganglion cells and displaced amacrine cells)
9. axons (nerve fibers from ganglion cells traversing the retina to leave the eye at the optic disk)
10. internal limiting membrane (separates the retina from the vitreous
We have focused on one of the sensing cells, the rod cells. The nerve cells that synapse with the rod cells and that we have assumed to have a “preprocessing” function would include the bipolar and ganglion cells:

Activated photoreceptors stimulate bipolar cells, which in turn stimulate ganglion cells. The impulses continue into the axons of the ganglion cells, through the optic nerve, and to the visual center at the back of the brain. There are about 120 to 130 million rods in each eye, and they are sensitive to dim light, to movement, and to shapes. There are about 6.5 to 7 million cones in each eye, and they are sensitive to bright light and to color.
This total to 130-140 million receptors!

From here:
There are approximately 1.1 million nerve cells in each optic nerve. The optic nerve, which acts like a cable connecting the eye with the brain, actually is more like brain tissue than it is nerve tissue.
Lets see: 130 million receptors funneled down to 1.1 million internet connections to the occipital cortex. 120 to 1. That’s a fair amount of processing in those bipolar and ganglion cells.

This just reemphasizes that information is preprocessed in the retina and that there is not a one to one mapping of image pixels (photons) to the brain.

And, you know, we haven't even touched on how or why evolution designed such a complex structure just to get the information from a few photons back to the brain. It is just amazing!


I had never thought much about “The Stars My Destination” since I read it in the late 50’s.

When it comes to pop culture, Alfred Bester (1913-1987) is something of an unsung hero. He wrote radio scripts, screenplays, and comic books (in which capacity he created the original Green Lantern Oath). But Bester is best known for his science-fiction novels, and The Stars My Destination may be his finest creation. First published in 1956 (as Tiger! Tiger!), the novel revolves around a hero named Gulliver Foyle, who teleports himself out of a tight spot and creates a great deal of consternation in the process. With its sly potshotting at corporate skullduggery, The Stars My Destination seems utterly contemporary, and has maintained its status as an underground classic for forty years. (Bester fans should also note that Vintage has reprinted The Demolished Man, which won the very first Hugo Award in 1953.)

Interestingly enough, I just read “The Demolished Man” and had no idea it was by the same author. I’m not sure how I got the name except that it might have been in a Wikepedia article on cyperpunk or something.

But, of course, “Tiger! Tiger!” caught my attention since a fragment of William Blake had come up when I Googled “Optic Nerve.”

Just go to Optic Nerve. There you will find this fragment of Blake's "Milton":
The Sons of Ozoth within the Optic Nerve stand fiery glowing.
And the number of his sons is eight millions & eight.
They give delights to the man unknown, artificial riches
They give to scorn, & their possessors to trouble & sorrow & care,
Shutting the sun, & moon, & stars, & trees, & clouds, & waters,
And hills out from the Optic Nerve & hardening it into a bone
Opake, and like the black pebble on the enraged beach,
While the poor indigent is like the diamond which, tho' cloth'd
In rugged covering in the mine, is open all within,
And in his hallow'd centre holds the heavens of bright eternity.

'Milton' - William Blake (1754-1827)

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Blake was not too far off if we assume he was talking about nerve fibers in the optic nerve when he mentions the Sons of Ozoth (don’t bother Googling "Sons of Ozoth", this guy only appears in Blake’s imagination; and doesn't his imagination sound like Lovecraft?) except 8 million vs 1 million is a little over the top.

But, back to “Milton” by Blake. This is one wild and crazy guy.

From here:

William Blake's "Milton" - Meaning and Madness

Most people know William Blake as the author of the poem The Tyger ("Tyger Tyger burning bright / In the forests of the night....") ……In his long narrative, "Milton", Blake describes how the author of "Paradise Lost" returned from heaven and entered Blake's foot in the form of a comet. Afterwards, the familiar world of the five senses turned into a shoe. Blake tied the shoe and walked with the Spirit of Poetry to the City of Art. A few years later, back in the ordinary world, Blake saw a twelve-year- old girl flying down to him. He mistook the girl for one of his own muses, and invited her into his cottage to visit with him and his wife, who could also see and hear "the spirits". The girl explained that she was actually looking for John Milton. The older poet emerged from Blake's foot, and in an apocalyptic scene, the ordinary world was transformed along with all of human perception.

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