Hermann Grid Illusion

The Hermann grid illusion is a visual illusion in which faint grey blobs appear to flicker at the intersections of a grid of white lines drawn on a black background (or dark blobs on a grid of black lines on a white background). The grey blobs disappear when the viewer looks directly at an intersection, so they are visible only in peripheral vision. First reported by the physiologist Ludimar Hermann in 1870, the effect is generally attributed to how the visual system processes contrast at the intersections versus along the plain lines, though the exact underlying mechanism is still debated among vision scientists. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/