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dslc1000

Logical heresy! (A visual experiment)

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(...If you feel (or even better - can prove) that anything I’ve written here is actually illogical, incorrect or that the values I’m using are inaccurate, please don’t hesitate to let me know...Otherwise, I’d love to hear if you agree with me...If so, we could discuss...)

 

In almost all circumstances, the images which fall on a persons retina are inverted. Because we don’t see our world upside-down however, the obvious conclusion is that the ‘act of seeing’ (perhaps for want of better terminology) does not take place at the retina, but in our brain, once it has somehow re-inverted the image - so that we see it upright. I think most people would accept a corollary to this theory: if the image formed on the retina was upright, then what we actually ‘see’ must be inverted - as the brain has ‘learnt’ to invert everything we see. But how can this corollary be tested? Very simply actually!

 

The reason that the image formed on our retinas is inverted is because of the refraction which occurs when light passes from air into the cornea and aqueous humour at the front of the eye, and also when light passes through the biconvex lens.

If the refractive power of the cornea/aqueous humour is removed, however, the refractive power of the lens is not enough to invert the image by itself. The value I’ve been able to obtain for the refractive power of the lens is 20 diopters at maximum (which means that parallel rays striking it would be focused at a distance of 5 cm - 1/20 meters - behind it).

 

A very simple way to remove the refractive power of the cornea/aqueous humour is to replace air with water. The reason this works is because water and the aqueous humour have almost exactly the same refractive index - that of water is usually given a value between 1.33 and 1.34; that of the aqueous humour is 1.336. What about the cornea? Well, the cornea has a refractive index of about 1.38, but this is irrelevant, as the opposite sides of the cornea can be considered as parallel for the purposes of this experiment (unlike the biconvex lens). Parallel rays travelling from water to the aqueous humor can therefore be considered as behaving as demonstrated in the attached "fig1.gif"

 

Because the refraction occuring between the two mediums (water and the aqueous humor) in this instance is effectively negligible, rays which are parallel at the cornea can be considered to be still parallel at the lens (see attached "fig1.gif").

Values I’ve been able to gather for the refractive power of the lens vary - anywhere from 10 (or even below) to 20 diopters. Therefore, parallel rays striking the lens will be focused 5-10 cm behind the lens. The distance from the lens to the retina, however, is only 1.4-1.7 cm. The image of the object in the water, therefore, is upright on the retina. According to the prevailing theory of visual awareness, we should therefore see the object upside-down, as our brain is supposed to invert whatever image is formed on the retina.

 

Try the experiment yourself! Take any object small enough so that the rays of light reflected off it into your eyes are parallel when the object is held at an arms length (or less) from your eyes, and which also has two easily-distinguishable sides (e.g. one side red; the other side white). Now submerge yourself in either fresh water or salt water (your bath; the sea; whatever - the difference between the refractive index of the two mediums is negligible - and no, this is not a joke :mad: ).

 

Now simply hold the object out in front of you (at a distance which ensures that the rays reflected off it into your eyes are parallel). It is difficult to see under water - quite a strain on the eyes in fact - but if the object you are using has two easily-distinguishable sides, you will see the image upright, although, according to the prevailing theory of visual awareness, it should be inverted. Note that you don’t even see a diminished image of the object (which is the very least you would expect).

 

(....These are my own original ideas, and I can readily verify this...don’t do anything silly like claim them as your own....)

 

EDIT (May 7th 2004): This is sooooh embarassing :embarass: , but it turns out that my argument is inherently flawed. See THIS thread to see where I went wrong.

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If this helps, it's been demonstrated that wearing goggles which invert the image before it reaches the retina causes the brain to flip the image after a few days.

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I'm not sure exactly what you're saying Sayonara - brain is a bit tired at the moment! That goggles help invert the image makes sense to me, as they restore the air-cornea interface, but let me stress...the experiment above is not to be carried out wearing goggles (...if anyone actually has the time or inclination to carry it out that is...). Nor was I wearing goggles when I carried it out myself.

 

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A pair of goggles designed specifically to flip the image, using mirrors, before it reaches the retina.

 

IE the wearer sees everything upside-down.

 

After a few days, the brain compensates and flips the image the right way up. Removing the goggles results in a few days of seeing everything upside-down before it flips back.

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In fact, my brain is smart enough to fix an image when I am upside down or on my side. I don't have problems reading or writing that way. In fact, it is hard for me to write in italic by angling the paper, because I automatically change my writing to fix it.

Sayo, that's true, I've seen a TV program about it and people could play catch with inversion goggles on (after a month wearing them).

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Sayonara:

Whatever about the brain adjusting its behaviour over a period of days - the notion that it can do so in an instant (as would need to be the case to disprove the above experiment) is very tenuous. In fact, your citation of this example consolidates the validity of the experiment, as it demonstrates just how long the brain needs to adjust its behaviour.

 

Cap'n Refsmmat:

I think perhaps you didn't understand what I was saying in my initial post. I can read upside-down too, but that has nothing to do with my point. In the experiment, its not that the brain merely makes decisions based on the visual information as if the object in the water is upright (as it does with the visual information from a book you are reading, even if it is upside down); You actually see the image upright.

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well since several million years of evolution has predisposed our brains to veiwing the inverted image as normalacy, I fail to see how it taking a few weeks to adapt can be at all significant?

In fact a few weeks or even months is quite impressive!

sayos point is perfectly valid! :)

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The "point" I was trying to make was that there is research out there that dslc1000 might find helpful in his investigations, but obviously he can do without it.

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I absolutely wasn't trying to knock what you were saying Sayonara - I hope it didn't come across that way (sorry if it did!) I am grateful that you made the point, as it seems to be very relevant.

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dslc1000 said in post # :

Cap'n Refsmmat:

I think perhaps you didn't understand what I was saying in my initial post. I can read upside-down too, but that has nothing to do with my point. In the experiment, its not that the brain merely makes decisions based on the visual information as if the object in the water is upright (as it does with the visual information from a book you are reading, even if it is upside down); You actually see the image upright.

If you were to put water in front of your eyes for a week or two, then you would be able to see normally, not like you described.

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actualy, even on a shorter period, sit in a room lit with green light for 10 mins, come out and everything will look pinkish :)

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they would see things in ordinary light as Greenish for a period of time, try it yourself, you will notice the change :)

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