 The Brain / Museum / Illusions / Sensitive Brain / Hot Spots |
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There appear to be dark dots in this display at the points where the white lines intersect. But as soon as you focus on them, they disappear. The mechanism that creates our illusionary perception of dark dots inhibits whiteness in areas that are surrounded by white. The areas where the white lines intersect are surrounded by a larger area of white than the white lines themselves, and they therefore "suffer from" greater inhibition of whiteness. We see the dark dots at every intersection we are not focusing our eyes on. This is because the inhibitory effect for whiteness is at the center of our field of vision. This is widely known as the Hermann-grid illusion, named for its discoverer. The evasive little dots can be explained in part by lateral inhibition, the same neural mechanism responsible for the Clear Boundaries and Lift the Strip! illusions. The intersections of the white lines are surrounded on all four sides by white. This white background causes strong lateral inhibition of our perception at these points of intersection. On the other hand, the white lines themselves are bordered by white on only two sides and our perception of them is less affected by lateral inhibition. The white lines therefore appear whiter than the intersections of those lines. Recently, the illusion has also been found to disappear under different circumstances - when the white lines are curvy rather than straight (see the first link below). According to researchers, this phenomenon cannot be explained by the lateral inhibition mechanism, since the intersections are still totally surrounded by white and the white lines themselves bordered by white on only two sides. And there is still no definitive explanation for the classic, straight-lined illusion and its disappearance. Related exhibits: Links:
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Hot Spots
