1. Penrose Stairs illusion
The Penrose Stairs illusion is also known as the Penrose steps. Lionel and his son, Roger Penrose created the illusion after they discovered the Penrose triangle.
This two-dimensional object is also referred to as the impossible staircase. It forms a continuous staircase whether you view it as ascending or descending.
The idea of this staircase is that it is never ending. If you were to climb or descend, you would never get to the end of it because of its continuity.
It is a two-dimensional staircase whose edges are connected at a 90-degree angle and the same cannot be replicated in three dimensions.
The Penrose staircase, like the preceding Penrose triangle, is a very famous optical illusion.
It was presented in a paper by Roger and Lionel Penrose written in 1959, a year after Roger had published the triangle of Penrose in the British Journal of Psychology.
Many people have tried to replicate the stairs into real life models.
2. Delboeuf illusion
The Delboeuf illusion deals with perception of size. When you look at the photo, one of the dark circles in the middle appears larger. This is based on the annulus surrounding the dark circle.
While the dark circles are both actually the same in size, it does not appear so because of the surrounding annulus.
The closer the annulus is to the circle, the larger it appears to be. In the same way, the further the annulus is from the dark circle, the smaller it appears to be.
The illusion is assumed to work through the same visual process as the Ebbinghaus illusion. This illusion’s practical application has been covered through a study showing how it affects eating habits.
The study in 2012 showed why people serve more food on larger plates that on smaller plates.
This is because the larger plate presents a smaller area covered by food thus influencing people to add more onto the plate.
3. Ebbinghaus Illusion
The Ebbinghaus illusion was discovered by Hermann Ebbinghaus who was a German psychologist. This is where the name of the illusion is derived from.
However, this illusion is also referred to as the Titchener circles because it is Edward B. Titchener who made it popular in the English-speaking world.
When you look at the two circles in the middle, one appears larger than the other. The circle surrounded by bigger circles appears smaller while the one surrounded by smaller circles appears larger.
In reality, both the central circles are of the same size. This is closely related to the Delboeuf illusion. The illusion deals with the perception of size.
A larger surrounding will make the circle appear smaller while a smaller one makes it appear larger. The distance of the surrounding from the circle also comes into play.
Further distance makes it look smaller while a smaller distance makes it look bigger.
4. Rotating Rings
The rotating rings illusion is one that many people do not seem to see clearly the first time around. The idea is to look at the center and stare at the dot for about thirty seconds to a minute.
Now move the image away from you and watch what happens. The circles or rings seem to be rotating in a certain direction. While the image is static, your brain perceives the image as moving.
As you see the circles moving, adjust your screen and move towards the image this time. The circles will appear to be rotating in the opposite direction.
The rotating rings, as some have tried to explain, do not actually work because of the difference in color as shown in the photo. Even with black lines and a white background, the effect is still achieved.
These rotating rings have been captured by artist Gianni Sarcone. Having an optical illusion turned into a work of art could add some fun to your home when hung on a wall.
5. Kanizsa triangle
The Kanizsa triangle is attributed to Gaetano Kanizsa, an Italian psychologist who discovered the illusion in 1955.
In this image, you can perceive an equilateral triangle in the middle even though it does not exist. Your brain forms and perceives boundaries because of the black shapes.
This illusion is used to explain that what we see is not just a sum total of parts. We can also perceive something more than what is defined by parts and boundaries.
It shows that we have holistic vision which is not only limited to what is defined. Psychologists have used this illusion to explain how we view closure.
Some things appear as a whole even though they are actually not part of a whole. For example, you perceive the three ‘pac-men’ as part of a whole in order to see the triangle in the maroon background.
6. Zollner illusion
The Zollner illusion is named after the German astrophysicist who discovered it.
It is one of the classical illusions as it was discovered back in the 19th century. Johann Karl Friedrich Zollner is the man behind this discovery.
He presented his discovery to another scholar and physicist Johann Christian Poggendorff who then discovered a related illusion.
This illusion shows that lines can be distorted by their background. In the image, there is a series of parallel black diagonal lines with shorter lines crossing these lines repeatedly.
The direction of these shorter lines is alternating with some crossing the diagonal lines vertically and other crossing horizontally. Instead, you perceive these lines as though they are not parallel.
The angle of the shorter lines on the diagonal black ones creates the impression that some of the diagonals are nearer than others.
This illusion has been likened to the Wundt illusion. The impression of depth is thought to be the cause of this illusion.
7. Hering illusion
Ewald Hering, a German psychologist, was the man behind the discovery of the Hering illusion back in 1861. The Wundt illusion offers the inverted effect of what the Hering illusion offers.
In this illusion, you can see that how you perceive lines can be affected by the background. This geometrical optical illusion features a radial background such as the spokes of a bicycle wheel.
In the foreground, there are two parallel lines. These parallel lines appear to be pushed outwards in the shape of a bow. There are a number of different explanations for why this effect is present.
The first is attributed to angle overestimation at the points of intersection. Another explains that there are temporal delays in the visual cortex which must be accounted for when perceiving objects.
Regardless of the explanation, it still remains that the lines do not appear in a straight line as they are in reality.
8. Poggendorff Illusion
The Poggendorff illusion was discovered by Johan Christian Poggendorff, a journal editor as he studied the Zollner illusion. There are two lines in this illusion and an object obscuring the lines.
The illusion and its magnitude are then influenced by the nature of the obscuring object’s borders as well as its properties. In this illusion, there is a continuous black-red line and a parallel blue line that is smaller than the former.
When these lines are obscured by a grey object or pattern, it appears that the line is blue-black and the red part of the black-red line seems parallel to the now black-blue line.
The illusion works with diagonal lines as the viewer perceives the acute angles as expanded.
This illusion is based on a number of factors such as the acute angles and the slope of the line. If you were to use vertical or horizontal lines then the illusion disappears.
9. Fraser spiral illusion
Sir James Fraser was the one who described the Fraser spiral illusion first. He was a British psychologist. It was initially known as the twisted cord illusion.
In the photo, the overlapping arcs form a spiral that narrows down all the way to the middle. In reality, these arcs are actually concentric circles.
The series of tilted elements causes the brain to see phantom deviations and twists which do not exist in reality. The misaligned parts trick your brain into thinking that these circles are actually one large spiral.
The illusion is thought to be based on similar principles as those of the Zollner illusion. The Fraser spiral illusion is emphasized because of the checked background.
You can see that the background can cause a distortion in how you view objects and shapes in the foreground. If you look closely, the illusion can lead to disorientation, similar to what cartoons use to represent hypnosis.
10. Hermann grid illusion
In 1870, Ludimar Hermann discovered the Hermann grid illusion. In this illusion, there is a grid that has black squares separated by white lines.
It can also be argued that these are black squares that are spaced, exposing the white background. The illusion is in the intersections of the white background.
When you look at this grid as a whole, you can see some grey blobs appearing in these white intersections. Ludimar referred to these as ‘ghost-like’ blobs.
Further to that, when you narrow down your view to just one intersection, the grey blob disappears on that particular section. A variation of the Hermann grid illusion is the scintillating grid illusion.
In this, there are black dots that randomly appear and disappear at the intersections. This is why it is referred to as scintillating. However, the black dot does not appear when you focus on just one intersection.