I think that Bananarama was close to giving the kind of carefully worded explanation I wanted.
I think I should ask a similar question:
Suppose a layperson stubbornly insisted and with overconfidence that the brain MUST physically flip the image the other way else we WILL all see the image upside-down;
What carefully worded argument could you give such a person that would almost guarantee that he would see error in his reasoning?
This is so far my best take on it so far:
I would explain to such a person that I think what he thinks is that, when we “see” something, there is an image in the brain that corresponds to the image on the retina (no problem there) but, and I think this is where such a persons reasoning is going wrong, that this image in the brain is there in a similar physical sense that the image on the retina in the sense that its physical orientation makes a difference!
I would then explain to him that the physical orientation makes no difference using the following Reductio ad absurdum argument:
Lets say, for the sake of argument, that the physical orientation of the image in the brain makes a difference. Now lets suppose a drunk brain surgeon opens up your skull to examine your brain, sees that nothing is wrong with it, and then clumsy puts it back into your skull upside-down and without breaking any brain or optic nerve connections (the optic nerves will have to be stretched and twisted a bit but otherwise left undamaged and fully functional and able to transmit signals through their entire length) and the retinas and your eyes both stay the same way up as before the operation.
After such an operation, would you see everything upside-down?
-if you think the answer is no, then surely you would now intuitively see that the physical orientation makes no difference.
-but if you think the answer is yes, then consider this:
every connection between any two given brain cell is exactly the same as it was before the brain was turned upside down except they are now physically upside-down but that has no effect on their behaviour and thus there cannot be any difference to the behaviour or processes in the brain and therefore there should be absolutely no difference in the perception of what is seen (including which way up it is perceived) because perception consists of certain processes in the brain and those certain processes, just like all of the processes in the brain, are unaffected by their physical orientation.
I am not sure if such a layperson would necessarily fully understand or be convinced of this explanation;
can anyone make a more convincing argument to such a layperson?