The science of "Snake-O-Vision"
If you've seen the serpentastic film Snakes on Plane, you're familiar with the movie's superb use of "Snake-O-Vision" -- the many moments when the camera shows a snake's-eye view of an impending attack. According to the movie, the snakes "see" their prey in green night-vision, with a round pinhole-camera-like center that's in focus, and a periphery that's blurry. Like everyone else in the movie theater, I laughed my head off when I saw it.
But then I wondered: How scientifically accurate is Snake-O-Vision?
As it turns out, the question of Snake-O-Vision has long puzzled scientists, particularly in two types of deadly serpents -- pit vipers and boid snakes. These snakes can strike prey with accuracy even when they're blindfolded, which suggests they're using a "pit organ" on each side of their head that senses infrared radiation. The problem is that these pit organs are one millimeter in size and not very deep -- which means they could produce only extremely blurry images. So how do the snakes do it?
A trio of German scientists now theorize that the snakes use firmware in their brains to error-correct the lousy imagery by harnessing the infrared noise produced by a moving prey. They built a neural-net model in a computer that mimics this, and fed it the actual data produced by a pit organ's 2000-odd receptors. Presto: It refined the blurry images into startlingly precise results. Check out the example above: There's the actual bunny, the blurry image from the pit organ (top right), and the result generated by their neural net (bottom right).
Okay, but how do we know this theoretical model matches what's actually going on inside the snakes' brains? We don't -- but the theory makes one superb prediction. It's this: If the pit organ generates even tiny errors, it would ruin the image. To minimize the errors in the scientist's model, the pit membrane would have to be no more than 15 microns thick -- one fifth the thickness of a sheet of paper. And that is precisely the thickness found in a real snake.
As one of the scientists, Leo van Hemmen, told The New Scientist:
"We've found a simple way that something seemingly impossible could work in the snake," he says. "If we could work it out, we're sure that nature could too."
A paper on the experiment was published this month in Physical Review Letters, but it is, alas, behind a paywall.
Posted by Clive Thompson at August 26, 2006 10:19 PM
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Clive,
I suspect the mechanism is something below "vision" in that the pit organ functions much like some of the lower separated visual functions that occur in mammals. Specifically, it is "sub-conscious" if you could call a snake conscious and it likely somewhat separated neurologically from the visual system of the snake, much like the tectal visual pathway is separated from visual cortex.
Given that in snakes the pit organ is connected through the equivalent of the trigeminal nerve, and that snakes do possess both rods and cones in their retinas, my guess is that the pit organ is a backup aiming device of sorts to be used in non visual environments.
Posted by: BWJones at August 27, 2006 6:45 PM
That's a very interesting read, but it opens up more questions than it answers. I'm presuming that the post referred to how well certain snakes can "see" with just their pit organs. If this is correct, this leaves open how well their eyes work when they are not blind folded. Also, I wonder why such redundancy? How well could a blind pit viper or boid snake get along in nature? How well could it get along with just its eyes? If not all snakes possess the capabilities of the pit vipers pit organs, do they possess something which is compensatorially comparable? If not, would we not expect to see a numerical ascendency of pit and boids?
Posted by: daniel luke at August 27, 2006 11:08 PM
BWJones, awesome analysis of it! Is the actual retinal vision of snakes reasonably good?
Daniel, yeah, that's a good question. Even we humans think we navigate primarily with our eyes, but we rely heavily on sound, touch, proprioception, etc., to figure out what's going on around us.
Posted by: Clive at August 28, 2006 11:24 AM
Clive,
Thats an interesting question as it is a little tough to do psychophysics on snakes, but they do have relatively well formed retinas with both rods and cones meaning there is likely some form of color vision. Be careful though as it is likely not vision as you or I know it. Their vision is likely geared more towards movement detection and assessment of general form as well as detection of overall ambient light for activity and circadian needs. I don't know a whole lot about snake behavior, but I suspect they are more chemosensory oriented than they are visually oriented as there is very little movement of the eyes possible in a snake, most do not have binocular vision and they have large apertures relative to eye size meaning relatively poorer visual acuity.
Posted by: BWJones at August 28, 2006 6:29 PM
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Clive,
I suspect the mechanism is something below "vision" in that the pit organ functions much like some of the lower separated visual functions that occur in mammals. Specifically, it is "sub-conscious" if you could call a snake conscious and it likely somewhat separated neurologically from the visual system of the snake, much like the tectal visual pathway is separated from visual cortex.
Given that in snakes the pit organ is connected through the equivalent of the trigeminal nerve, and that snakes do possess both rods and cones in their retinas, my guess is that the pit organ is a backup aiming device of sorts to be used in non visual environments.
Posted by: BWJones![[TypeKey Profile Page]](http://www.collisiondetection.net/nav-commenters.gif)
at August 27, 2006 6:45 PM
That's a very interesting read, but it opens up more questions than it answers. I'm presuming that the post referred to how well certain snakes can "see" with just their pit organs. If this is correct, this leaves open how well their eyes work when they are not blind folded. Also, I wonder why such redundancy? How well could a blind pit viper or boid snake get along in nature? How well could it get along with just its eyes? If not all snakes possess the capabilities of the pit vipers pit organs, do they possess something which is compensatorially comparable? If not, would we not expect to see a numerical ascendency of pit and boids?
Posted by: daniel luke![[TypeKey Profile Page]](http://www.collisiondetection.net/nav-commenters.gif)
at August 27, 2006 11:08 PM
BWJones, awesome analysis of it! Is the actual retinal vision of snakes reasonably good?
Daniel, yeah, that's a good question. Even we humans think we navigate primarily with our eyes, but we rely heavily on sound, touch, proprioception, etc., to figure out what's going on around us.
Posted by: Clive![[TypeKey Profile Page]](http://www.collisiondetection.net/nav-commenters.gif)
at August 28, 2006 11:24 AM
Clive,
Thats an interesting question as it is a little tough to do psychophysics on snakes, but they do have relatively well formed retinas with both rods and cones meaning there is likely some form of color vision. Be careful though as it is likely not vision as you or I know it. Their vision is likely geared more towards movement detection and assessment of general form as well as detection of overall ambient light for activity and circadian needs. I don't know a whole lot about snake behavior, but I suspect they are more chemosensory oriented than they are visually oriented as there is very little movement of the eyes possible in a snake, most do not have binocular vision and they have large apertures relative to eye size meaning relatively poorer visual acuity.
Posted by: BWJones![[TypeKey Profile Page]](http://www.collisiondetection.net/nav-commenters.gif)
at August 28, 2006 6:29 PM