Hermann Grid Illusion

Hermann Grid

In this illusion, dark grey circles seem to appear at the intersections of the white lines on the dark grid. If you look directly at an intersection, the circle at that intersection will disappear.

Scintillating Hermann Grid

Another version of this illusion is the scintillating Hermann Grid. In this version of the illusion, white circles are present at all of the interesections of the grid. When looking at the illusion, it seems as if dark dots are rapidly appearing and disappearing from the intersections. If your eye is kept on a single intersection, no dot will appear there and any dots that are too close or too far from that intersection will also disappear.


The explanation that is most commonly used to explain both of these illusion is a neural process called lateral inhibition. Lateral inhibition is based on the fact that we use retinal ganglion cells gather information from more than one photoreceptor. When one photorecptor detects light, it becomes excited. However, the surrounding photoreceptors inhibit the cell. This inhibition leads to the area appearing darker than it actually is.

Now lets apply this process to the Hermann Grid. When you look directly at an intersection, it is being looked at with your fovea which has very little lateral inhibition allowing you to see it clearly. However, the intersections in your peripheral vision experience a great deal more lateral inhibition which makes them appear darker than they actually are which leads to the dark dots appearing.

Lateral inhibition is the most common theory, but it is not the only one. In fact, some people disagree with it on the basis that it does not take into account certain outcomes. When the lines of the grid are made slightly wavy, the illusion is stopped which lateral inhibition theory could not predict. In addition, lateral inhibition would make it seem as if decreasing the size of the grid would cause the illusion to stop because of decreased lateral inhibition. This is not true. Another explanation could be that the illusion is caused by the S1 type simple cells in the visual cortex.

What does this tell us? 

Even though there isn’t a consensus on why the illusion occurs, it still teaches us the very important lesson that our eyes see things that are not there and therefore are not one hundred percent accurate all of the time. If the lateral inhibition theory is to be believed, then it also tells us that our brain may change the colors in an image in order to better display it.


2 responses to “Hermann Grid Illusion”

  1. Laura Kloepper says:

    What do you think is the mechanism for this illusion?

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