Perceptual adaptation

I am sure you have heard that the image of an object created on your eye’s retina is inverted (rotated by 180 degrees). The brain however has the ability to processes this information in such a way that makes you see things as they really are. This fact is remarkable and can give us a hint of how complex perception of reality is.

Fig.1. The image of real objects that is formed on our retina is inverted as compared to the original object. This happens due to the existence of the eye lens. However, we still do not perceive our environment as inverted.
Fig.1. The image of real objects that is formed on our retina is inverted as compared to the original object. This happens due to the existence of the eye lens. However, we still do not perceive our environment as inverted.

In the 1890s George M Stratton started out to test the theory of perceptual adaptation. He wanted to test whether the brain would be capable of adapting to radical (external) changes in the visual system. For this purpose he constructed a device that reversed the image of a physical object. The device’s principle of operation is shown in fig.2. The image of the physical object would be inverted once by the optical device he wore and once again by his eye lens. Practically speaking, although the image on his retina would have the same orientation as the physical object, the brain would interpret things as being upside-down. The reason is that the human brain has been used to considering the inverted image of the retina as the correct orientation of objects.

In Stratton's experiment an optical device was used so that the image that reached the retina was not inverted as compared to the original object.
In Stratton’s experiment an optical device was used so that the image that reached the retina was not inverted as compared to the original object.

And this is exactly what happened. When Stratton wore the device he saw everything upside down. Keeping the device on for a little less than a day he did not notice any changes after taking it off. In a later experiment he kept the device on for 8 days. This time removing the device had created confusion. According to Stratton’s account, he had grown accustomed to the reversal of everything the previous days, and after removing the device he felt that the scene was given “a surprising, bewildering air which lasted several hours”. His conclusion was that “harmony comes only after a tedious course of adjustment to the new conditions, and that the visual system has to build anew, growing from an isolated group of perceptions” [1].

Researchers still debate whether it is our behaviour trying to adapt to the new inverted reality, or our vision. Would it be possible for our vision to adapt completely so that we would see objects as they really are if we wore the device for long enough. By taking the device of would we see everything upside down and a new cycle of adaptation would be required? Maybe the brain would co-ordinate all functions and movements in such a way that although everything would look upside down we would be able to function. The results are not conclusive.

To understand how difficult it is to function when the world suddenly becomes upside down just turn your computer screen upside down and try to point something with your mouse. You do not really need to move the screen you can do it from the graphics setting as shown in fig.3 below.

How to rotate the screen on a Windows 7 computer with Intel(R) HD Graphics processor. Most graphics cards give this option somehow. If you cannot find the setting try the following shortcut: Ctrl+Alt+down arrow key. The same shortcut with the up arrow key should restore the screen orientation to normal.
Fig.3. How to rotate the screen on a Windows 7 computer with Intel(R) HD Graphics processor. Most graphics cards give this option somehow. If you cannot find the setting try the following shortcut: Ctrl+Alt+down arrow key. The same shortcut with the up arrow key should restore the screen orientation to normal.

George Stratton had more interesting things to say. For example he believed war was caused by intentional delusions held by nations (which are groups of people). He also wrote a book about that. This is an interesting observation. We may get back to this in another post.

References

1. Wade Nj. Guest editorial: An Upright man. Perception 2000;29(3):253-257.

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