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Why do we turn images upside down again rather than dealing with them directly, still vertically rotated after passing through our lens?

I don't see how that would cause any problems, and how we'd ever be able to figure out if we are presented with flipped images after getting used to interacting based on visual input, whether flipped or not.

What am I missing?

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My head of Biology has regularly mentioned an experiment where individuals were given glasses that inverted their vision - after a period of time their brain compensated and re-inverted the image (presumably the same happened when the glasses were removed). Interesting stuff - I'll see if I can find a link. – Rory M Mar 30 '12 at 19:10
That'd be appreciated :). – Chris Mar 30 '12 at 19:28
So, what is the exact question you are asking? The title asks something different from the question's body... – nico Mar 30 '12 at 19:36
Closely related question on CogSci.SE – jonsca Mar 30 '12 at 22:10
The question assumes there is something like a little projection screen inside the brain -- something that has an "up" and a "down". It's not like that; there are just an array of retinal cells transmitting pulses to a set of neurons. Retinal cell A talks to neuron 1, cell B to neuron 2, etc. neurons 1 and 2 are not physically arranged in space in a way that matters to image perception. There is no little man in there watching a little screen. See the CogSci question that jonsca linked to. – mgkrebbs Mar 31 '12 at 7:15
up vote 5 down vote accepted

The basis of this question is a common misconception, and unfortunately the accepted answer by @CHM is also based on this common misconception. The misconception is based on the homunculus falacy and the tendency for people to think that the image that lands on the retina is somehow 'assembled' and presented for something (the 'consciousness') to view. This is not the case.

As the comment by @mgkrebbs expains, there is no orientation (up or down) in the brain, there is only neural firing. The infromation of the visual scene is distributed over the brain, and information does not have physical properties like orientation. Although as @nico pointed out the neurons that process the information do have a spatial structure that mimics that of the retina, this is a topological property (i.e. simuli that are close on the retina are processes by neurons that are close in V1) and such a topological property does not induce an orientation.

The root of the problem is really that the question "How do we know the brain flips images projected on the retina back around?" is a pseudo-question. Although it is grammatically well-formed, it makes no semantic sense. When the image is 'in the' (i.e. being processed by the) brain it no longer has physical properties like orientation. Thus you cannot ask if it has been flipped or not.

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So is the retinotopic arrangement inverse top-to-bottom of the input from the retina? In that case it's still a valid question why the pathways from one half would at some point cross over with those from the other half and not just stay on the side they are. – Armatus Jun 17 '12 at 9:10
@Armatus: that is a different question from the "upside down" problem though (which, by the way, on the retina is a purely physical issue do the lens that turns the image upside-down). – nico Jun 17 '12 at 15:01
@Armatus The cross-over is a good question, and you should ask it on CogSci.SE. However, I feel that the question (and the accepted 'answer') was instead about the lenses vertical and the common misconception of orientation of images in the brain, not about why we have opposite hemispheric mapping.. – Artem Kaznatcheev Jun 17 '12 at 15:08

I think you're oversimplifying the problem. Think about gravitation.

Take this informal example: at any point on a massive sphere, you can define "bottom" such that any massive object with weight less than that of the sphere is subject to an attractive force towards that point. The direction of the force points in the direction of the "bottom".

Assuming this holds true for every massive object, the following is logical: for the purpose of orientation, it is a lot more energy efficient for an organism to simply invert the image using brain circuitry than invert every single sensory input to effectively reverse the definition of "bottom", which follows from physical laws to which the organism is invariably bound.

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