Optical illusions

Synonyms in a broader sense

optical illusions, visual illusion

Definition

Optical illusions or optical illusions are perceptual illusions of the sense of sight, i.e. of seeing. These can occur in almost all areas of vision, for example, there are the:

  • Depth illusions
  • Color illusions
  • Geometric illusions
  • And many more.

Optical illusions are caused by the visual system misinterpreting a visual stimulus. An image that we ultimately become aware of is not created solely by objective information from the eye and nerve cells, but is only created in interaction with our brain.

So what we finally perceive is subjective and results from processing a visual stimulus with existing experiences and memories. With the help of additional information from the other senses or by removing triggering factors, optical illusions can often be shown and proven. In the psychology of perception, optical illusions are investigated, since they allow conclusions about the further processing of optical stimuli in the brain.

Gestalt psychology uses optical illusions by systematically producing and analyzing them. There are practically an infinite number of different optical illusions, but they can be divided into different groups according to their origin. Especially the perception of differences in brightness is very subjective.

In twilight, the same color tone appears much brighter than in strong sunlight. For this reason, a gray bar, which has the same gray value everywhere, appears brighter even in a dark environment than in a bright environment. The brain can also interpret the relationship between light and shadow.

The brain has made the experience that an object looks darker in the shadow. It therefore attributes a lighter coloration to the same hue when it suspects it is a shadow effect, since the color “only became darker through the shadow”. If you fix your eyes on a green square for about half a minute and then look directly at an adjacent white area, a reddish square appears.

This is because we see a so-called afterimage on the retina in the complementary color of the previously viewed object (complementary colors: red-green; blue-orange; purple-yellow). The negative afterimage is caused by the fact that the color receptors in the retina practically “tire”. After a permanent excitation that lasts at least 30 seconds, these receptors temporarily “go blind”, which means that they no longer send signals to the brain.

In the time it takes for them to regenerate, the signals of the complementary colors then predominate relatively, so the actually white area appears red. In optics, too, everything is relative. Our brain does not evaluate a figure by itself, but always in context.

A circle surrounded by many small circles therefore appears larger than a circle of the same size surrounded by many large circles. The impression of “relatively” larger or smaller is thus transferred. Furthermore, an image is always evaluated as part of the three-dimensional world.

This means that when processing images, the brain assumes from experience that objects become smaller with increasing distance from the eye. In images that give us the impression of spatial depth, objects or people of the same size appear smaller at the bottom of the image than at the back. This type of optical illusion can be used in architecture, photography and film to make certain objects appear larger or smaller or closer or further away to the eye of the observer.

There are many optical illusions where the viewer believes that parts of a picture would move. To create this illusion, in some cases the head itself has to be moved, but sometimes not. The movement is usually noticeable in those places that are not focused by the eye at that moment.

An illusion of movement is always created when you look at an (often small) object that is located in front of an environment that does not give any indication of its spatial position. Lines that are actually straight can appear crooked to the viewer if the overall impression of the image is irritated by different color plays or other disturbing elements, for example. As a result, straight lines often appear curved.Even two parallels can appear skewed to each other, if other lines in the surrounding area interfere with the overall image.

This phenomenon of optical illusion was first described by Hugo Münsterberg in 1874 and is for this reason also known as the “Münsterberg illusion”. When processing visual information, the brain amplifies already existing contrasts of images. With a white grid on a black background, an observer thinks he sees gray spots of color light up at the intersections of the white lines because the contrasts are overemphasized.

However, the gray patches can only be seen as long as one does not concentrate on them. Because this observation was first made by Ludimar Hermann, the grid is accordingly also called the Hermann grid. When processing visual impressions, the brain focuses very much on lines and edges, because they provide orientation for it.

It also tends to try to rediscover familiar patterns when recognizing them. Consequently, lines and edges are added during perception, which then serve to create a known object. As a result, when looking at an image with circles that have recesses in certain places, for example, one imagines that a white triangle is visible.

Some objects can be perceived in multiple ways from different perspectives. These include the so-called tilting figures like the Necker cube. Here, our individual experience determines the position in which the figure (the cube) is preferably perceived, although one is still able to comprehend both views.

The term “tilting figure” comes from the fact that the cube seems to tilt when one concentrates on one position of the cube during longer observation. In various areas of everyday life, optical illusions can be used to achieve certain effects. In film, for example, the illusion of movement is exploited, whereby the rapid succession of individual images creates the illusion of movement.

In painting, too, some optical illusions are used as stylistic devices, for example to achieve optical enlargements. On the other hand, of course, unwanted optical illusions also occur in everyday life, which trick our perception, which can lead to confusion. Under certain circumstances, for example, roads seem to lead downhill, which in reality run uphill, and vice versa.

The phenomenon of the illusion of movement can be observed, for example, whenever a single star is in a dark sky, which then seems to move. Optical illusions are an integral part of our daily life. They are based on the fact that our perception is subjective and objective external stimuli are strongly influenced by the brain and already made knowledge and experiences.

We often perceive optical illusions only unconsciously or do not realize that we are succumbing to an illusion until the switching off of the triggering factors or the drawing in of information from the other sensory organs proves the opposite. This is exploited in various fields such as film, painting or architecture. Further interesting information from this field of ophthalmology: An overview of all previously published topics from the field of ophthalmology can be found at Ophthalmology A-Z

  • Explanation of an optical illusion
  • Red- Green- Weakness
  • Color Blindness
  • Examination of color vision