Figure 4 in the article [1] is absolutely fascinating and seems to prove conclusively that the edge detection hypothesis is completely misguided: when one retai

Figure 4 in the article [1] is absolutely fascinating and seems to prove conclusively that the edge detection hypothesis is completely misguided: when one retains only the edges (B) of the original image (A), all meaning is lost and the resulting image is unrecognizable. What A has that B lacks is shapes. There is obviously a rotund shape of the face that is reconstructed by the brain, that one can almost see, although technically it's not actually present in A. Not present, yet visible. Same for the eyes, smile, cheekbones. It must trigger some kind of pattern-matching in the brain. This problem seems to be similar to the famous optical illusion of the old woman / young woman [2] that works well also in strict black and white. In this optical illusion there is surprisingly little information on the image, yet it can trigger two very different representations (that one can see alternatively, but never at the same time). I think the brain tries to fit the shapes it sees in one box or another, and when it finds a box it builds a whole concept around it. I also think that boxes have to pre-exist or be learned: they can't be inferred from an image, if one has never encountered the original representation in the wild. One evidence for this is children are completely blind to optical illusions that have one "innocent" representation and one involving some kind of nudity or sexual activity, while adults tend to see the NSFW version first. And so, to come back at the original question of why line drawing works, I think it's because it triggers concepts. The word "square" or "circle" are unambiguous and designate precise geometric shapes (provided one has learned the relevant concepts of square and circle). Same with shapes, except that there are an infinite amount of different shapes that we can "discuss" using the language of line drawings. [1] https://aaronhertzmann.com/images/howtodraw/sayim.jpg https://aaronhertzmann.com/images/howtodraw/sayim.jpg [2] https://cdn.mos.cms.futurecdn.net/rQkQZ6pDZbEHz23rxckWPm-320-80.jpg https://cdn.mos.cms.futurecdn.net/rQkQZ6pDZbEHz23rxckWPm-320...