Mach Bands - Edge Enhancement Illusion
The side of a higher intensity (brighter appearing) stripe near the lower intensity (darker appearing) stripe appears brighter than elsewhere across the stripe. Physically the stripes are uniform across their full extent. Likewise, the darker stripes are uniform across their full extent but appear darker on the side near the brighter stripes. We can ask what causes this appearance of brighter and darker regions near the other stripes. Inhibitory connections ("wiring") among retinal neurons affect signals transmited further into the visual system. The connections are such that the more intense stripes cause more inhibition and therefore the appearance of the darker region on the darker appearing stripes. The connections are also such that the less intense stripes cause less inhibition and therefore the appearance of the brighter region on the brighter appearing stripes.
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