Kreds

We are very accustomed to gridded views. Not only looking through the gridded windows, but when we walk along the streets, blocks of houses, shops by the sides, with light or darkness coming through them, build our respective impression strong through the absorbed memories of grid views. Neglecting the curvature, the earth's surface is horizontal, and on it gravitational force is perpendicular. For that, our world is more horizontal and vertical in nature than any other form. And this is the reason behind Hermann-Grid optical illusion. In Hermann-Grid illusion, we challenge 'the possibility' and 'the impossibility'. If the inside light is so bright to make the grid complete white, the darkness beyond the grid could not be as dark as complete black due to reflection and scattering of light by the grid. When we look at a bright light source, there appears a hallow around it due to scattering of light by the atmospheric molecules and particles. The darkness around the light source is smudged with same tinge of colour. To watch background as dark as complete black, the insight should be less lighted or the grid should be darkish. So the illusion appears at the peripheral vision which lies between the possibility and the impossibility. In Lingelbach illusion the borders have already been smudged with darkness. So the illusion does not appear at the borders as we are accustomed to see that type of darkness only through that colored grid. In the vice versa case, if the background is bright white, bright yellow, bright red or of any bright colour, and the grid is of different colour, the illusion would also appear, because due to scattering of light, and to some extent reflection of the light from the inside objects including the observer, the grid will have a tinge of that colour. So for theoretical purpose, for easier understanding, whether the background is dark or bright we can presume that background is scattering its own colour to produce its effect on the grid. Now, why the darkness or smudge (effect) is more prominent at the intersections? – It is because of overlapping areas of scattering halos (from four quarters) at the intersections. Why we do not see the illusion when the grid is tilted at 45 degree or the shape of the grid is changed? Because we are not accustomed to see those views. We don't see any more those as usual familiar views; we just see those as a design or a painting that does not challenge our memory.

https://scholar.google.co.in/scholar?hl=en&as_sdt=0%2C5&q=role+of+pre-embedded+associated+memory+in+generation+of+optical+illusions&btnG=

researchgate.net/publication/327550772: Role of Pre-embedded Associated Memory in Generation of Optical Illusions 5b960ada299bf1473937f891.pdf

Hermann Grid Illusion : The Mystery Unveiled The current study infers, optical illusions are more related to associated memory of us rather than optical factors, retrieval of which can occur reflexively. Optical illusions take the route to betray our firmly embedded associated memory. According to researcher Dr. Krishanu Das, optical illusions are more related to associated memory of brain. Associated memory means sets of memories associated with different objects and situations. For that, whenever we see a cup, we expect to see ' tea' or 'coffee' within it. Or whenever we look at the sky we anticipate to see 'stars' or 'clouds' in it. Retrieval of these associated memories may be triggered reflexively. Optical illusion takes the route to deceit the retrieval of the firmly embedded associated memory. Whenever we see an image, we cannot concentrate on every point of it. We concentrate our vision on a particular point, which is known as focal point. Our peripheral vision is partly constructed on imagination and understanding of overall impression of the image. Our focal vision though challenges impossibility, our peripheral vision does not challenge impossibility, instead it lies between possibility and impossibility. In case of a firmly pre-embedded associated memory, our mind often perceives the image according to the pre-instituted memory and knowledge, rather than actual image, particularly in peripheral vision. Fig.1 : Hermann-Grid illusion. Darkness appears at the intersections of the grid which dissipates also along the borders (named after Ludimar Hermann who discovered it, 1870). Fig.2 : Lingelbach illusion. A variation of H. G. illusion. Dark dots appear and disappear at the intersections (after E. Lingelbach, 1994). Explanation for Hermann grid illusion, is grid illusion is more related to the associated memory, rather than optical factors. In Hermann grid illusion, our peripheral vision simply anticipates reality, as like in reality we are accustomed to see the views of grid in different light shades. Source : 'MIND: A Comprehensive Study on Mind and Its Dynamics' by Dr. K. Das