How is “brain supplementation” achieved?

Humans know the world through their senses, and most of the time, their senses faithfully convey information, telling us what exists and what is happening in the world. But sometimes, our senses go awry, and we have all kinds of strange illusions.

Escher is a famous master of optical illusions. In his paintings, the stairs that lead to the second floor somehow return to the first floor, birds become fish in constant change, waterfalls fall from a tower tank that is like a perpetual motion machine, and two lifelike hands outline each other on paper... His painting style was regarded as heresy by the art world for a long time, but he was regarded as a confidant by many mathematicians, architects and philosophers, and was popular among young people.

Japanese designer Nobuyuki Chihara created a dynamic optical illusion of a "rotating dancer". The direction of the dancer's rotation changes with the viewer's perspective: from the left, it seems that the dancer is rotating clockwise; from the right, it seems that the dancer is rotating counterclockwise. Nobuyuki Chihara cleverly used the details of visual persistence, light and dark contrast, posture and shadow to create an "arbitrary" animation.

The existence of illusions is not a defect of the brain. On the contrary, the brain is too "smart" and always wants to make analytical judgments based on existing information. When we see a table lamp, we don't see every detail of the table lamp, but the brain has already outlined the overall impression of the table lamp. The parts that are not seen are "filled in" by the brain with speculation. The brain always makes quick fillings based on past experience. This filling is correct most of the time, but sometimes it can be wrong.

The brain has "constancy" when judging the size of objects. Although objects in the distance may look small, the brain will judge them to be relatively large, and surrounding reference objects also help to assist in the judgment. "Constancy" works in many cases: when a person walks from a distance, the image on the retina becomes larger and larger, but we know that his height has not changed. The Ames room destroys this "constancy": after the room was modified, the distance from the left corner to the observer is almost twice the distance from the right corner to the observer, but it seems that the two people are at the same distance from the observer, but the observer thinks that the person in the right corner is taller (in fact, their heights are equal).

We also encounter illusions in our daily lives. It is well known that the moon appears larger when it is high on the horizon than when it is high in the sky. The size of the moon and its distance from the Earth have not changed, so the moon on the horizon and the moon high in the sky should appear the same size. Why does the moon appear larger on the horizon? One reason is that when the moon is on the horizon, you have to look over mountains and hills to see it, so it appears farther away; while when the moon is high in the sky, the sky is empty and it appears closer. Another reason is that when the moon is high in the sky, the vast sky surrounds it, making it appear smaller; when the moon is on the horizon, the sky surrounding it is smaller, making it appear larger.

Illusions are confusing, but they also have their special uses. Zhuge Liang's "borrowing arrows from a straw boat" took advantage of the foggy weather and Cao Cao's suspicious character, turning the scarecrow on the boat into a strong general in the eyes of the enemy. During World War II, the British magician Jasper "moved" Alexandria from under the noses of the German army in a very short time, making the bombing plan fail. There are even more examples of using illusions in the commercial world: installing more mirrors and lights in a small house will create the illusion of expanding the space; plaid clothes or fluffy hairstyles will create the illusion of slimness for plump people; wearing 3D glasses will create the illusion of bullets whizzing.

Illusions are not only caused by vision, but also by hearing, smell, taste, touch, etc. Let's do a small experiment: cross your index finger and middle finger, and then touch a small round object, such as dried peas, and you will feel as if you have touched two peas. When you cross your fingers, the two sides of the two fingers that do not normally touch each other "meet", and the sense of touch is transmitted to the brain from the two sides of the fingers. Under normal circumstances, the two sides of the fingers will hardly touch the same object at the same time, so the brain cannot recognize that the fingers have been crossed and "takes it for granted" that they are two peas.

Broadly speaking, illusions also include incorrect reasoning and judgment. For example, if the price of a product is set at 99 yuan instead of 100 yuan, consumers will have the illusion that the price is low; if a movie is played during the journey, passengers will have the illusion that time is passing faster; compared with hard-earned money and money won from lottery tickets, the latter often gives people the illusion of "low value", causing many "lucky" lottery winners to squander it.

The world is so strange, how can we know right from wrong? Let us be more aware and think, and we will be closer to the truth.

(The author is an associate professor at Central China Normal University and a member of the Chinese Society for Neuroscience)