Taking a Look at the Hermann Grid

If you’ve been reading the Museum of Illusions NYC blog for a while now, then you might already be acquainted with the illusion that we are going to talk about today. The Hermann Grid is one of the best examples of a physiological illusion. We broke down the three different types of optical illusions in this post, so jump over there after this to brush up on your physiological illusion knowledge.

For now, stick around to learn about the discovery and the function of a trippy little optical illusion- the Hermann Grid.

The Discovery of the Hermann Grid

The Hermann Grid illusion was first discovered by a German physiologist named Ludimar Hermann. He noted the illusion in a physics textbook where there were figures printed in a matrix arrangement. Almost simultaneously, a man named Hering noticed the same illusion in a black and white grid figure. This is why you will sometimes see it being referred to as the “Hermann-Hering Grid.”

A Hermann grid used for the Museum of Illusions NYC blog
The Hermann grid. Hint: if you can’t see the ghostly grey dots, scan your eyes across the image without focusing on one spot.

Even though the Hermann (or Hermann-Hering Grid) is named after these two men, it was first formally reported by David Brewster in 1884. Brewster gave credit for the discovery of the illusion to Reverend W. Selwyn.

While the truth behind the discovery of the Hermann Grid is a little foggy, the science behind it isn’t. Frequent readers will know that frustratingly often we have to end a blog post with “no one knows why or how this illusion occurs.” Well, the 150-year-old Hermann Grid illusion is a bit different, let’s talk about how it works.

How Does the Hermann Grid Work?

Take a good, long look at the Hermann Grid illusion pictured above. You see a grid made of black squares and thick, white lines. You probably also see ghostly grey dots or smudges where the lines cross over one another. However, the grey spots aren’t actually a part of the image. They are an illusion.

The illusion tricks your eyes because of the contrast. Your retina is trying to adjust the intensity of the image, but the intersections of the grid fall out of the scope of your retina. This means that your eyes can’t sharpen the image for you, and the little grey smudges appear. You might notice that when you stare intentionally at one of the intersections you don’t see the grey spot in that section. That is your retina doing its job.

Illusion or Hallucination?

Just because we know how it works doesn’t mean that there isn’t a little bit of mystery surrounding the illusion. In fact, some argue that it’s not actually an illusion at all. 

The key difference between an illusion and a hallucination is perception. Illusions are when your brain inaccurately perceives something, hallucinations are just seeing something that isn’t there. It’s a fine line, but the difference lies in the brain.

Many philosophers believe that it leans more toward being a hallucination, but the fact that the “hallucination” occurs because of the brain’s perception of the grid leaves some room for individual interpretation. What do you think- illusion or hallucination?

Either way, we think the Hermann Grid is pretty cool. If you think it’s cool, too, then you will love everything that we have to show you at the Museum of Illusions NYC. Click here to book your visit!