Smoke and Mirrors: Cognitive Optical Illusions Explained

Do you ever feel like your eyes can’t be trusted because they’re fooling you? Take a look at these photos below:

road painting optical illusion

perspective visual optical illusion

Paper thin building optical illusion

They look confusing, don’t they? If you’re near these places, you would probably grab your monocular or binoculars just to take a closer look at their details, trying to find the flaws. But I’m telling you now; there’s an explanation behind those seemingly unexplainable optics.

We usually come across optical illusions in magic shows. These illusions are created by our visual system and are distinguished by visually perceived images that deviate from objective reality. Our eyes gather information which is processed in our brains. The brain will then give a perception that does not agree with an actual measurement of the source. Optical illusions can either be literal optical illusions, physiological, or cognitive. Today, we’ll only explain the last type.

Types of Cognitive Illusions

These illusions are believed to exist because of the speculations about the world we live in, leading to unconscious inferences. This was first suggested by Hermann Helmholtz, a German physicist and physician, in the 19th century. Under cognitive illusions, there are distorting illusions, ambiguous illusions, paradox illusions, and fiction illusions.

Distorting Illusions

These are also referred to as geometrical-optical illusions because they are characterized by distortions of length, position, size, or curvature. One of the most famous examples is the Ponzo Illusion which shows two lines that appear to have different lengths, but in reality, they have the same length.

Ponzo Illusion, distorting cognitive illusion

Ambiguous Illusions

On the other hand, these are objects or images that generate a perceptual “switch” between alternative interpretations. A well-known example is the Rubin Vase which depicts a vase when you focus on the white part but shows two people facing each other when you concentrate on the black portions of the image.

Rubin vase illusion

Paradox Illusions

These are produced by objects which are paradoxical or out of the question like the Penrose triangle. This example becomes an illusion because we were used to the fact that adjacent edges should join.

Penrose triangle, paradoxical illusion

Fiction illusions

They occur when a figure is perceived although it is not in the stimulus.

Cognitive Illusions Explained

Perceptual organization

Let’s take a look at another ambiguous illusion called the Rabbit-duck illusion. Gestalt psychologists believe we need to organize incoming sensations into meaningful information by perceiving individual sensory stimuli as a whole. This is why the illusion below is reversible.

Rabbit-duck optical illusion

Depth and motion perception

Remember the Ponzo illusion under distorting illusions? This type of illusion is based on our ability to see in 3D even though the image hitting our retinas is only 2D. These types of illusions are caused by our brain exaggerating what we see. In the Ponzo illusion, the brain creates a false perspective that the other line is longer than the other because it is farther away.

Color and brightness constancies

In the illusion below, it would seem like the horizontal bar, with a color gradient from dark to light gray as its background, appears to progress from light gray to dark gray. If you try to cover the background with your fingers, however, you will realize that the horizontal bar only has one color.

Color and brightness optical illusion

This illusion is created when the brightness or color of the area around the unfamiliar object is changed. It would then seem that the contrast of the object is darker against the black portion which reflects less light compared to the white field, though the object didn’t change its color at all. To sum it up, the eye doesn’t just look at the color of the object, it also considers the color of the surrounding area, creating an illusion.


So whenever you see optical illusions that appear to be playing with your head, better think twice. It might be your own head playing with you!