Let's do a fun little experiment together:
Cross the middle finger of one hand over the index finger, then gently slide the crossed fingertips on the tip of your nose, paying close attention to the sensation transmitted by your fingers.
How about that, do you feel like you're touching what seems like two noses?
Image Source: IASP 2024
By touching the corner of your phone in the same way, or touching a small circular object like a soybean, you can feel as though you are touching two objects.
In reality, this sensation is an illusion.
It was actually discovered over two thousand years ago by the ancient Greek "encyclopedic" scientist Aristotle, and is therefore also known as the Aristotle illusion.
Aristotle mentioned in "Metaphysics": "When we cross our fingers, touch tells us there are two objects, while sight tells us there is one object." (Book 4, Chapter 6)
How are illusions created?
Aristotle's illusion is known as "perceptual segregation."
When we cross our index and middle fingers and touch our nose, the outer sides of these two fingers touch the nose, and the touch sensations from these two sides are sent separately to the brain.
Normally, the inner sides of these two fingers touch the tip of the nose. Since the outer sides of the two fingers hardly ever touch the same object simultaneously, the brain mistakenly perceives that it has touched two noses.
Touching the tip of the nose with the outer sides of two fingers. Image source: lhecht
The explanation for this phenomenon can also rise to a philosophical level.
French philosopher and phenomenology master Merleau-Ponty believed that the "Aristotle illusion" is related to the body schema:
The body schema can be simply understood as the habitual movements of the body and the possibilities of perception. Habitual movements and possibilities of perception refer to the actions that a subject usually performs or can perform, and crossing fingers is a "voluntary action" that goes beyond the natural movement of the fingers.
For this reason, the body schema cannot consider the crossed fingers as an organ pointing to the same movement or intention.
Therefore, the two crossed fingers act separately and generate individual sensations that cannot be unified in a single perception.
Why is the brain so prone to illusions?
Nobel laureate and cognitive psychologist Daniel Kahneman believes that evolution has made the brain very stingy in allocating and using cognitive resources, "if the brain can avoid working, it will avoid working," and in order to cope with the rapidly changing world, the brain often chooses to sacrifice some "accuracy" in exchange for "speed."
How is this achieved? Through "experience."
"Experience" is a computational shortcut that the brain has established to pursue speed. By using certain pre-established assumptions, the brain can save a lot of resources.
For example: the brain assumes that objects appear smaller when they are far away; the brain assumes that the color of an object itself usually does not change arbitrarily, and if it does change, it is due to changes in the brightness of the light source or the color itself.
Classic Image: Is the dress you see blue and black or white and gold? Image Source: Internet
These experiences become experiences because the above-mentioned characteristics (such as near appears larger, far appears smaller) are generally constant and unchanging in most situations. They help us quickly recognize and understand the world.
Therefore, in the process of evolution, they have become the brain's inherent way of extracting information.
However, there are always exceptions. For example, the "unnatural things" and "unnatural actions" constructed by humans in the previous text. If the brain still tries to understand them in its inherent way, it can lead to illusions and make us "fall for it".
This can also be understood as bugs that arise due to the brain's imperfect evolution.
Illusions also contribute
Although illusions are considered bugs of the brain, they have significant contributions in many fields.
For example, in the field of research, they can provide scientists with unique perspectives, helping them understand how the brain processes information, constructs perceptions, and makes decisions. This is of great significance for advancing the fields of cognitive science, psychology, and neuroscience.
Aristotle's illusion contributes to Parkinson's disease research. Image Source: Brain
In interior design and architectural planning, illusions are often used by designers to alter spatial perception. For example, clever use of mirrors or color combinations can make a small space appear more spacious and comfortable.
Friends living in large houses can skip this one.
Illusions are also "veteran actors" in film and animation production.
The famous Hitchcock zoom fundamentally applies visual illusions, achieved by zooming in or out with the camera lens to keep the foreground in the same position while compressing or stretching the background, creating a wonderful sensation for viewers.
Aristotle's illusion is just one of many illusion phenomena, revealing the limitations of how our brains perceive the world.
However, it is these limitations that drive us to continually explore, study, and improve our cognitive systems.
It also helps us realize that science is not an unreachable mysterious realm; it actually hides in the bits and pieces of our daily lives.
References:
[1] "Judgement under uncertainty: Heuristics and bias"
[2] Aristotle’s illusion and the enactive embodied situated approach to perception
[3] Aristotle’s Illusion in Parkinson’s Disease: Evidence for Normal Interdigit Tactile Perception | Brain | Oxford Academic
