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Comment by elcritch | Hacker News Reader

Flipping the eyes is the same geometric reasoning the article discusses. The same thing applies to touch and motor control too.

Its just a general extrapolation of the same principle. It would also explain why creatures without sight as well like many worms.

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I think the eye example is in fact different because light passing through the lense is inverted onto the retina as the root comment explains, there's no such inversion for perceiving other senses. I find the explanation intuitively appealing at first, but given connections are criss crossed for far simpler animals such as worms like you mention, I don't think the idea that vision is the primary driver of this phenomenon is correct.

It's not different, because the left-right flip by the lens is part of a rotationally symmetric image translation (that also flips up for down, e.g.), not a bilaterally symmetric reflection. With the rotation, there is no change in the relationship of parts of the image one to another, relative to our personal orientation, the way there is in the reflection, so it's trivial for the brain to account for it - up on the retina is always down in the real world, left on the retina is always right in the real world, etc.

I think the point you're making is that orientation of the image is arbitrary, and the original commenter agrees that's the case for one eye: "If we had only one eye, there would be no issue, the image would appear as a continuous image, just flipped around."

But we have two eyes, so if you directly connect the two inverted images observed by each retina, there would be a discontinuity in the middle of the joined image (peripheral light from the outer sides of each eye would be mapped to the middle of the joined retinal image). The original commenters point was that criss crossing the neural connections from the retina would resolve this discontinuity, allowing the brain to process a continuous image.

> It would also explain why creatures without sight as well like many worms

This would require that worms evolved the cross crossing independently, after our common ancestor, which doesn’t seem to be clear [1].

All it would take is a few light receptors to get the cross cross party started.

[1] https://www.sciencedaily.com/releases/2010/02/100201101905.h...

Those kind of light receptors don't have the lenses that cause our eyes to flip the image. They are omnidirectional and usually not even on the surface of the critter. Just a small bag of rhodopsin that triggers a nerve to depolarize. I think the geometric arguments in the article make sense in that context as well, the same way they would for a chemotactic or pressure sensor.

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