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Comment by squillion | Hacker News Reader

After an explanation that without L/R crossing the body map in the brain would be flipped upside down, comes this revealing passage:

"To make sense of the sensation [...] your brain would have to switch from one somatotopic map to another one with the opposite z-axis orientation".

This a textbook example of the "Cartesian theater" fallacy. It assumes a little person inside the brain who has to deal with an image projected upside-down. Of course that doesn't make sense.

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Slightly related: there’s a YouTube video [1] of a guy teaching himself how to ride a bicycle “in reverse”, i.e. you turn left, and it goes right. It takes some practice but in the end it just “clicks”. So now he’s balancing and moving completely opposite to perception.

So you’re right about the little man. I struggle to see why some arbitrary axis transform is “too hard”.

[1] https://youtu.be/MFzDaBzBlL0

I vaguely remember reading about some similar experiments with goggles that mirrored vision. As I remember, after a few days, people can mostly overcome the difficulties of having their vision reversed.

I also have a vague memory of this but can't find any sources for it. I wonder if we're both hallucinating?

to counteract your point though he does struggle a lot, and he does find riding the bicycle the usual way very hard after that. if you watch the video you can see him falling over and over

But that’s probably because it’s two sets of muscle memory competing for the exact same space. It’s like when a new game decides to reinvent controls, and every reviewer slams it for “janky controls”, because we have years of training in a particular layout. That’s why we have the concept of “unlearning things”, because the brain is really good at learning things, even wrong things. But that sounds to me to be an entirely different discussion than “brain orientation”.

The pictures with the finger at the end are even more confusing. They conflate the mapping from body parts to cerebral cortex (the cortical homunculus) with the mapping from the homunculus to some other part of the brain were the 3D environment is allegedly mapped. They don't make sense to me.

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