Brain "learns" light

Interpretation of light and surrounding environment characterized by experience

Hole or bump? Assuming that the light comes from the top left, the left part of the picture is interpreted as a crater and the right as a hill. Assuming, on the other hand, that the light comes from the bottom right, the interpretation revolves, and the left part of the picture is seen as a bump on the ceiling, and the right part of the picture is a hole in the ceiling. But this second interpretation is for most Viewers are much harder to see because our perception is trimmed to the interpretation of "light from above". If you turn the picture upside down, you see how the interpretation hole / bump reverses. © Max Planck Institute for Biological Cybernetics
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In order to interpret the complex stimuli that constantly affect us, our brains use assumptions about the environment. Scientists at the Max Planck Institute for Biological Cybernetics and the University of Southampton have now shown that basic assumptions, such as the light coming from above, are not genetically anchored in humans, but are adjusted according to specific experience. This demonstrates the special ability of the human brain to adapt flexibly to changing environmental conditions, the researchers said in a pre-publication in Nature Neuroscience.

On the one hand, it is the information from the various sensory organs, such as the eye, nose or skin, that determines our perception. On the other hand, prior knowledge and assumptions about our environment also play a role. This interaction between momentary sensory information on the one hand and previous knowledge on the other can be impressively demonstrated using examples. Thus, for most observers, a crater can be seen on the left part of the picture. On the other hand, the right part of the image is usually perceived as a hill. Both interpretations are not unique. You can tell immediately, if you turn the picture upside down - now the interpretation of the pictures should be reversed. In fact, the two images are exactly the same image, except that the right version is rotated 180 degrees.

All a question of viewpoint

How is this ambiguous interpretation? In order to interpret the image, the brain makes assumptions about which direction the light is coming from. Since the light in our world mostly comes from above, through the sun, overhead lighting or the like, it is reasonable for the brain to use this prior knowledge in interpreting the images. Under this assumption - the light comes from above - it is the only "correct" interpretation to see the left part of the picture as a crater and the right one as a hill. However, if our brain made the assumption that the light came from below, the interpretation would turn around exactly - the left part of the picture would be seen as a hill and the right one as a crater, but not on the ground, but on the ceiling. Mathematically, this interplay between sense information and prior knowledge can be described very well with the theory of probability developed by Bishop Thomas Bayes in 1763, in which the prior knowledge is described with the aid of "Prior", the "a-priori probability distribution". In the illustrated example, there is a prior for "light from above".

Eye tricked by sense of touch

Marc Ernst from the Max Planck Institute for Biological Cybernetics in T bingen, together with his colleagues Wendy Adams and Erich Graf from the University of Southampton, has now investigated the question of how the brain comes to such presumptions: are these innate and thus genetically determined or can such fundamental priors, such as the "light from above" assumption, be learned from the frequency of occurrence? To do this, the researchers used ambiguous stimuli similar to those in the left picture and examined the perception of subjects before and after an interactive training session. In this training, the subjects could not only see the stimuli, but also scan for about 1.5 hours with their fingers. The trick was that during the training, the visual image and thus the range of light incidence, in which the objects feel like a hill, was rotated by 30 degrees. As a result, the sensation did not always match the visual perception, and some of the objects that were seen as a hill before training now felt like a hole and vice versa.

The result of these experiments was that, as a result of this interactive training, the perception of the test subjects actually changed - some of the "craters" were suddenly seen as "hills". The researchers found that the "light from above" assumption was turned around on average by about eleven degrees. Since the apparent brightness of an object usually depends on its orientation to the incidence of light, a general change of the "light from above" assumption should also change the perception of the brightness of objects. In fact, it turned out that the subject's subjects appeared differently bright after the training - in accordance with the change in the assumed light direction. display

Dogs are less flexible

The researchers thus succeeded in proving that even such fundamental assumptions as the "light from above" assumption are not genetically anchored, but constantly based on the statistical regularity with which they are used in the Environment occur, learned within a relatively short time and adapted. However, this is in contrast to experiments conducted with other species, such as chickens, which also make a "light from above" assumption, but which appears genetically anchored in these animals. All in all, these results underline the extremely good adaptability of the human brain and that the perception differs from person to person depending on the individual learning history and previous knowledge.

(Max Planck Society, 08.09.2004 - ESC)