Part2 This grid, known as Hermann's Grid, is an example of how contrast affects color perception. Imagine the Hermann Grid as a map of city streets; most crossings appear to be gray, but when you look closely at any individual crossing, you will see that it is white. The streets, on the other hand, appear white no matter where you look. This illusion depends on high contrast black and white areas to fool the eyes into perceiving gray areas. The perception of gray crossings is a result of local brightness control in the retina. Cells in your retina set the brightness of an image by the intensity of the light signal. But your brain can set the brightness of an image in many small parts. Setting brightness in small parts lets you see a wide range of both bright and dark parts in the same image. In Zollner's illusion of direction, parallel lines appear to be bent when other lines cross them at an angle. The illusion disappears when the image is held far enough away from the eye to distinguish the short crossing lines. Some scientists say that face recognition is performed by a particular section of the brain. To the brain, this image of Lincoln's face looks normal when viewed upside down, but when turned around it becomes distorted. This is because our brains recognize a face only when it is right side up. When it is presented upside down, the brain no longer recognizes it as a face but rather as an object, and this is why we do not respond to its distortions.
