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If you hear a squish, that's too far
Apr. 14th, 2005 12:09 amI went to another math lecture last night, this one on "Dynamic Instabilities in Neuroscience," by Bard Ermentrout of Pittsburgh. It was pretty nifty.
An example in plain English: if you press on your closed eyes, after a few seconds you will begin to see purple mosaics or sunbursts or spirals. (These patterns are similar to the ones seen by users of LSD, people with migraines, and shamans on happy weed.) The pressure, you see, puts your optic nerve to sleep, just as falling asleep on your arm might put the nerves there to sleep. The input effectively drops to zero, so you see nothing for a little while. (I verified this by pressing—carefully—on my open eyes, and I did indeed go blind when the patterns started.)
But some nerves in your visual cortex get a little random boost from background noise, and rise a little above the norm. These excited cells suppress their neighbors, which means the neighbors of the neighbors are unsuppressed, so the neighbors of the neighbors of the neighbors are suppressed—and these self-organize into a stable pattern, so you wind up, soon enough, with a nice regular pattern of stripes or checkerboards of excited cells in your visual cortex. The visual cortex maps via a polar transform to your retina, so the stripes become concentric circles ("tunnels") or spirals or rays in your field of vision, depending on their angle. (Checkerboards map to a circular mosaic.) As waves of excitation pass through your visual cortex, these shapes appear to move, spinning or expanding or contracting (depending on which direction the waves are traveling), and you get a nice light show.
Anyway, the talk was a bit scattered, but Bard was entertaining; at one point, he said, "Now, on the back of your handout..." [Pause while everyone flips the handout over.] "...if you lick the lower right-hand corner, you'll see what I'm talking about." And he mentioned The Brain from Planet Arous, for which I, at least, extend mad propz. I asked him whether he'd used cellular automata to simulate this self-organizing pattern formation, and indeed he had, dissing Wolfram in the same breath. Interesting fellow. Clearly he'd...experimented.
An example in plain English: if you press on your closed eyes, after a few seconds you will begin to see purple mosaics or sunbursts or spirals. (These patterns are similar to the ones seen by users of LSD, people with migraines, and shamans on happy weed.) The pressure, you see, puts your optic nerve to sleep, just as falling asleep on your arm might put the nerves there to sleep. The input effectively drops to zero, so you see nothing for a little while. (I verified this by pressing—carefully—on my open eyes, and I did indeed go blind when the patterns started.)
But some nerves in your visual cortex get a little random boost from background noise, and rise a little above the norm. These excited cells suppress their neighbors, which means the neighbors of the neighbors are unsuppressed, so the neighbors of the neighbors of the neighbors are suppressed—and these self-organize into a stable pattern, so you wind up, soon enough, with a nice regular pattern of stripes or checkerboards of excited cells in your visual cortex. The visual cortex maps via a polar transform to your retina, so the stripes become concentric circles ("tunnels") or spirals or rays in your field of vision, depending on their angle. (Checkerboards map to a circular mosaic.) As waves of excitation pass through your visual cortex, these shapes appear to move, spinning or expanding or contracting (depending on which direction the waves are traveling), and you get a nice light show.
Anyway, the talk was a bit scattered, but Bard was entertaining; at one point, he said, "Now, on the back of your handout..." [Pause while everyone flips the handout over.] "...if you lick the lower right-hand corner, you'll see what I'm talking about." And he mentioned The Brain from Planet Arous, for which I, at least, extend mad propz. I asked him whether he'd used cellular automata to simulate this self-organizing pattern formation, and indeed he had, dissing Wolfram in the same breath. Interesting fellow. Clearly he'd...experimented.
