What is a perceptual illusion? Illusions are anomalous perceptual experiences in which information deriving from external, real stimuli, leads to a false interpretation of the object or event from which the stimulus comes. Perceptual illusions are, in essence, the result of incorrect interpretations of a series of sensory data to the point that it is possible to perceive them in contrast with the real data coming from reality.
It seems that there is a sort of error in the processing of sensory input information from the central nervous system. All of this could be due to competing sensory stimuli that affect the meaning of the stimulus itself, such as, for example, when a car driver perceives his or her headlights reflected in a shop window, experiencing the illusion that another vehicle is moving towards itself, even though it is aware that there is no road ahead.
Perceptual illusions: the story
The term illusion derives from the Latin noun illusio-onis, which means mockery, mockery, error, illusion. It generally indicates an error coming from a sensory perception that leads to falsify reality.
Perceptual illusions were already an object of interest among the ancient Greeks. Aristotle for the first time presented what he called the illusion of the waterfall: we observe an object in motion and then move our gaze to a stationary object; it will automatically appear to us in motion. But, perceptual illusions have become a real object of study with the advent of experimental psychology in the 19th century.
Perceptual illusions: what are they?
The sensory receptors in the brain are able to detect light, sound, scent, temperature, and any other sensory stimulus. Each of them has specific areas on the body attributed to the recognition of the stimulus, such as eyes, ears, nose, hands, etc. From these sense organs, the brain receives sensory stimulations, which most of the time it interprets adequately, but if not, then a sensory illusion occurs. From now on, we will focus not on all sensory illusions (every sense organ could run into an illusory interpretation of the stimulus) but only on perceptive ones.
A perceptual illusion consists of an image that does not actually correspond to the one actually perceived because it appears different.
An illusion can occur following prolonged visual stimulation, such as observing a light source for a long time. The image that remains imprinted on the retina when you look away from the source is a physiological illusion. The perception, therefore, can be modified due to an imbalance caused by an over or hypo stimulation of the receptors present on the retina thus leading to the occurrence of a perceptual imbalance.
Some of these perceptual illusions may derive from factors that are not entirely controllable, such as when the light waves make a pencil immersed in a glass perceptible as folded, or when in low light conditions we are able to perceive several images at the same time, or some things appear to us further or closer than the real distance, etc.
A perceptual illusion can therefore be of three types: ambiguous, distorted, and paradoxical.
Ambiguous perceptual illusions are images or objects that allow the viewer to have two valid interpretations of what the object represents. The observer is usually able to mentally visualize an interpretation immediately and, finally, the second, after a certain time. However, both interpretations cannot be seen at the same time because that would interfere with the full perception of either one, and the brain simply does not allow it. An example is the Necker cube, in which it is difficult to say whether the represented angle emerges from the figure or is at its base.
Distortion perceptual illusions are images or objects that are distorted in their geometry: size, length, position, curvature. An example of an illusion is that of Muller-Lyer, where two separate lines with arrows at the two ends of each row appear to be of different length, instead they are exactly identical.
Finally, a paradoxical illusion or fictional illusion is an image or object that is simply impossible to represent three-dimensionally but becomes such by depicting it two-dimensionally. One of the best examples of a paradoxical illusion is the Penrose scale. It is a two-dimensional image but we perceive it as three-dimensional. This illusion is possible because in the figure it is possible to falsify the angular perspective to the point of bringing out a dimension that does not exist in the figure.
Therefore, the illusion is a misrepresentation of a true sensory stimulus, that is, an interpretation that contradicts the re Perceptual illusions: what are they?
Numerous optical illusions are those produced by the refraction or bending of light as it passes through a substance or object. Therefore, a ray of light that passes from a transparent medium such as air to another such as water determines a bending effect of the beam itself. A very familiar illusion produced by refraction is the Rainbow effect: the sun’s giving rise to a spectrum of colors: the rainbow. Another illusion deriving from atmospheric action is the mirage, in which, for example, the vision of water is created by the light that passes through layers of air placed above the heated surface. In fact, the colder layers of the air reflect the sun’s rays to create an illusion of water where there is any.
Furthermore, our brain is able to group together meaningless scattered objects giving them a meaning that objectively do not have. All these happen on the basis of acquired similarities, or with respect to how close or distant these objects are to the observer.
The illusion of closure, which has already been discussed in the previous article regarding Gestalt is the illusion of perceiving a stimulus that is not complete as complete. In other words, a sort of completion of the figure occurs. For example, if a person watches a film, the closure occurs when the intervals are filled in order to create an illusion of continuity with the uninterrupted image.
The figure-ground illusion, one of the best known perceptual illusions, occurs when two can emerge from an ambiguous figure, such as the white vase or the outline of two black profiles. Fluctuations from one figure to the background can also occur without active effort, but clearly perceiving one aspect usually excludes the other.
The Poggendorff illusion depends on the slope of the intersecting lines, in fact if the slope is decreased the illusion becomes less convincing.
In Zöllner’s illusion, two or more parallel lines appear to converge when they are intersected by inclined segments with opposite angles. This effect occurs because the segments disturb the perception of parallel lines.
In Ponzo’s illusion, a figure seems larger than another figure of the same size placed between parallel lines drawn in perspective. This illusory effect is obtained because the linear perspective creates a perceptual error: parallel lines, like railway tracks, seem to converge in the distance. Of course, we all know that this is not the case.
A real perceptual illusion that has happened to everyone is the moon illusion. When the Moon is on the horizon, it appears to be much larger than when it is high in the sky. Still, it’s always equally great. So why is it perceived differently? It seems to be a problem of lack of distance signals felt in the night sky that cause ocular dispersion that makes the moon smaller.
Illusions vs hallucinations
The illusions called pseudo-hallucinations occur when emotions such as anxiety or fear are projected onto external objects. For example when a child at night is able to perceive monsters or goblins in the shadows or tree branches that come to life. This phenomenon is also found among soldiers, who in a state of fear confuse people or objects for the enemy, to the point of directly launching an attack. This pseudo-hallucination is also present in the literature. Who does not remember Don Quixote confusing windmills for enemy knights? And in the end, he lost the battle!
A different thing occurs in psychiatric patients who perceive people as machines, teddy bears, and devils, in this case they are real visual hallucinations.
Something very similar happens with the déjà-vu phenomenon, the feeling of having already experienced a present episode in the past. There is a sort of fusion between past and present that creates the illusion that an experience that has already been made is being relived, but it is only an illusion due to the presence in the current scene of something that recalls the past. Some define it as a true hallucination, since the familiarity of the present content reactivates old memory traces of similar situations experienced in the past.
Furthermore, emotions, associations, and expectations often cause illusory perceptions in everyday life as they emotionally charge a situation to the point of making it perceptually distorted or illusory.
Perceptual illusions: theories
There are numerous theories formulated to explain how perceptual illusions occur, and the most important will be reviewed below.
Theories based on the role of eye movements. When an illusion occurs it is easy for eye movements or saccades to be made only in a certain direction of the figure, to the detriment of the others that are ignored or underestimated.
Neurophysiological theories. Initially, when little was known about the brain, perceptual illusions were thought to depend on physiological characteristics of the retina. Subsequently, when it was demonstrated the existence in the visual cortex of neurons specialized in detecting the orientation of the stimulus, the level of production of the illusion was shifted to this brain area. For example, the illusion that a vertical segment is perceived longer than a horizontal (or oblique) segment could be explained by an optimal sensitivity of neurons for vertically oriented stimuli and a reduced sensitivity of neurons that respond to other orientations.
Psychological theories. It is possible to distinguish three main ones: empathy theory, Gestalt theory, cognitive theories. The theory of empathy is based on the hypothesis that a dynamic relationship is established between the observer and the stimulus, whereby the observer evaluates the stimulus according to affective and emotional resonances. Gestalt theory, which was widely discussed in the previous article. And finally, cognitive theories, which consider illusions to be errors in the interpretation of the stimulus.
Cultural factors. According to some scholars, perceptual illusions depend on cultural factors that lead to having a direct influence on the percept. Thus, the illusion of the line would occur in Western populations accustomed to processing visual-spatial information and not in populations living in open spaces
Our cognitive unconscious on the basis of experience, “bets” that things are in a certain way and therefore bypasses uncertainty by making us fall into the trap of optical illusions.Our brain anticipates sight by a few thousandths of a second and confuses us with optical effects.Put simply, when light hits the retina, it takes about a tenth of a second before the brain translates the perceived signal into visual information of the surrounding world.
Researcher Mark Changizi of Rensselaer Polytechnic Institute in New York says our visual system has evolved to compensate for these neural delays, generating images of what will happen in the next split second. This innate “future clairvoyance” that we possess is however, as well as a source of optical illusions, the way of seeing the present in which we live.
We can afford to catch a ball on the fly without catching it on the big face! Or we can avoid taking a tronata against a pole, while we walk through the streets of the city! As you can see, this foresight theory has a lot of positives.
How to explain optical illusions?
The theory of foresight can explain many common visual illusions such as geometric optical illusions:
Hering illusions in which two horizontal lines are parallel but appear convex in the center; Although the figure is static, a false curvature is perceived.
Changizi therefore argues that evolution has caused some geometric designs to arouse premonitions in us of the near future.
How many times, looking at lines that converge towards a vanishing point (the spokes of a bicycle rim), do we have the sensation of moving forward?
How is it possible to be duped by optical illusions? Our intuition invents them from scratch. The image of the retina is two-dimensional but the brain “extracts” and interprets lights, shadows and shapes in its own way.
Optical illusions function as intuitive judgments, those approximate judgments that we apply in everyday life. In any situation in which we find ourselves confronted with insufficient information, we lack the desire or the time to think about it, we “bet” that things are a certain way. Some bets we win, some we don’t!
The brain works like a statistic
The way we see reality depends only on our brain processes, in fact scientists often say that “if we had a brain that used different strategies to understand the world, the latter would be very different”.
So what do these images have that baffle him so much? Inaccurate lines, floating objects, strange perspectives. The retina captures all these data and immediately sends them to the cerebral cortex so that it processes and interprets them, but the issue is that the retina only captures these images in two dimensions, therefore being limited information in which it focuses only on seeing. edges, colors and shapes… there is too much disorder, there is no balance and the brain is immediately disoriented.
So how does it work? By means of statistics. Unable to understand what he is seeing, he puts his hand to his statistics after extracting the information he has available and draws a conclusion: for him the image we are seeing has the ability to move.
However it is not certain, because obviously our rational part tells us that it is impossible, the paintings cannot move, but it makes us believe it.
Types of optical illusions
In practice, there are two types of optical illusions.
1. Cognitive illusions: as we explained earlier, the brain misinterprets the information sent by the eyes and makes a mistake in deducing the size and perspective of objects. Let’s see an example:
What do you see, two faces or a cup?
2. Physiological illusions: it happens when you are dazzled or the retina suffers a slight stress in looking at a certain object to which it cannot adapt. You could have what is called afterimage or consecutive image, that is when a figure remains imprinted in our eyes because there is a lot of light and a lot of color and we blink.
Gaze at this image for 30 seconds and then move your gaze to a white wall. What you will see will be the afterimage.
All of this leads us to the interesting conclusion that the perception of things is not always what we think. PERCEIVING ALSO MEANS INTERPRETING; our world as we see it is not an exact reflection that has a direct impact on the brain through the senses, on the contrary, our brain analyzes, synthesizes, transforms and interprets. They are not deceptions, but simply a way of protecting us from the unknown and that in the face of disorder gives a balance and an answer that is as logical as possible. Thanks to the brain we adapt to the world around us and, without a doubt, it makes it more exciting.
How optical illusions work
Some get nervous, others like them, but each of us, beyond the pleasant sensation or not that he experienced, at least once, the first, found himself wondering how optical illusions work. The scientific explanation exists and it is not that complex to understand. Indeed it is certainly simpler than many apparent visual paradoxes that our mind has to face precisely because of these “magic”. Faced with optical illusions, our brain begins to show us things that seem absurd. Why are you making fun of us so? Let’s find out!
How optical illusions work
The protagonist, the advocate, is as you have understood the brain, the eyes are partly accomplices partly victims. Optical illusions are inventions designed specifically to challenge the physical limits of our brain which, while trying to do its best, cannot transform us into super heroes. It has its own reaction speed that it cannot and cannot overcome. From the moment we see a certain image with our eyes until the moment it reaches the brain which is then able to process it, time passes which seems minimal but which allows the inventors of optical illusions to make fun of us. It is something like a tenth of a second, in which anything can happen and it causes us to actually see the images in deferred.
The mind is aware of this and organizes itself to circumvent this delay, from its attempt the optical illusions take place. There are several studies on the subject, those published and those still in progress, there is for now “a truth” about how optical illusions work but some theories seem to be more interesting and accredited than others. From the Rensselaer Polytechnic Institute in New York comes the following. According to the researchers of this institute, the brain is aware of its speed limits in processing fast and different visual stimuli, so it tries somehow to predict what will happen in the future based on what it has already processed, what it knows for sure.
As we all know, correct predictions are not always obtained based on the historical data but our brain has that and that it uses to try to keep up with a rapidly changing reality that stimulates it in a too rhythmic way. Even technological development, which gives us 3D visions and increasingly effective perspectives to represent our world, often requires the brain to make an extreme effort and when it feels it cannot succeed, it foresees, as it can, deluding us, precisely, to see things that There are. Between images and videos, and even objects, there are many optical illusions of different types, sometimes you can guess where the pitfall our brain falls into, sometimes not. Let’s see some of them.
The former do not depend on human physiology but only on optical phenomena, the latter instead arise precisely from a misleading human perception, such as those that appear after staring at a certain image for a long time, when the eyes are finally closed (posthumous images). Cognitive optical illusions are created directly by the brain which, as we explained earlier, interprets images in its own way, deceiving us just as happens in the presence of perspective paradoxes.
Types of optical illusions and examples
Only with a few examples, ranging among the many cases of optical illusions, we can better understand the beauty of this phenomenon and the complexity that our brain and our body carry inside.
In geometric illusions, it is the very geometry of the image that is perceived badly, so for example parallel lines seem to diverge, or if they are curved they seem straight or vice versa. Equal segments appear to be of different length and so on. We play with colors, with thicknesses and with lights to deceive the brain, but it is not a useless game made just for fun. In architecture, many of these techniques for distorting dimensions become invaluable for playing to make facades, houses and rooms look different from what they are, usually larger than reality.
Those who are experts in cinema, especially those of the past, can testify that they often doThose who are experts in cinema, especially those of the past, can testify that tricks of geometric illusion are often used to insert large objects into the film, using small ones. Another type of optical illusions very useful in practice is that of perspectives, explicitly used to make flat images appear three-dimensional. In doubt, the brain perceives a volume and this is how it happens with the Necker cube. Try to find it and experience how your brain behaves.
So far we have played with lines and dimensions, but colors can also deceive us and, approached in a certain way, appear different from what they are. Two different shades of the same color are enough to make us appear two identical areas, different in size. A well-known example of this type of effect is certainly the Adelson Chessboard in which two squares are the same color but everyone would swear that one is different from the other.
When the brain is busy in its fury predicting the future, afraid of not keeping up with all the stimuli we send, the illusions of completion are created. In this case we see lines that are not there, we imagine them with the mind as logical consequences of what we have perceived. Similarly it happens with the illusions of movement that at times make us see still images in motion while at other times they can even cripple real movements by varying their direction or direction. In the “illusion of the wagon wheel”, for example, we end up perceiving an object such as a wagon wheel as it turns at high speed, stationary or even rotating in the opposite direction.
Browsing through the various types of optical illusions we find distorted figures, ambiguous figures and impossible figures.
The first are images that have undergone a strong deformation, are “disfigured” by it but there is a certain perspective from which one can still perceive their identity. Leonardo da Vinci used this technique in some of his notes. Ambiguous figures are those in which we can see two or more images, recognize them distinctly according to points of view or expectations. We end with the impossible figures that depict objects in two dimensions, pretending that they can have three dimensions, but on closer inspection this is impossible. The master of impossible figures is certainly MauritsCornelis Escher. About Escher, and how optical illusions work, you can find beautiful posters online with his works that call us to reflect on reality and illusion. These are 70 × 100 panels, comfortable and useful for our walls. You can find them at this link
The illusion of knowledge: why is “knowing it” important?
Have you ever heard of the Dunning-Kruger effect? If you are passionate about psychology, most likely yes, also because it dates back to 1999. That is the little brother of the illusion of knowledge.
When I tell people who “know less than what they know” the first response is one of profound distrust and then they think it is the “discovery of hot water”.
Unfortunately, this is not the case and I believe that knowing these mental mechanisms in depth can be of great help … good listening:
In this aphorism of the great philosopher and mathematician B. Russell the whole episode of today is condensed: the less we know something, the less tools we have to know how much we know!
I know this phrase sounds like a “supercazzola” but I can assure you that it is not. Our knowledge of the world around us has evolved through “approximations and simulations”.
Just think if one of our ancestors had to know all the fauna and flora that surrounded him before he could move around the world, we would surely have become extinct.
Instead our brain has the fantastic ability to move in unknown environments without necessarily having to understand everything but simply relying on what it “thinks it knows”.
The more complex things are, the more we are forced to rely on such approximations, we do not do it because we are “stupid or simple” but because this allows us to survive in unknown environments.
Whenever we have mentioned the functioning of our “cognitive system” we have talked about “cognitive economy”, that is, the fact that the brain constantly tends to save energy.
He does not do this only because it was once difficult to get food but because if he were to pause to weigh all the variables involved he would become a victim of the “paralysis of analysis”.
But while one of our ancestors may have suspected that he “does not know everything”, today with the advancement of science and the possibility of knowing everything “with a click” things have “got worse”.
In the sense that we seem to be able to know things, because in reality we know a lot more, but our brain continues to remain lazy and prefer simplifications.
And all this has been exacerbated with the possibility of being able to access information online, where people believe that having knowledge available is knowing!
Umberto Eco’s anti-library
Umberto Eco divided the visitors to his home into 2 categories: those who merely complimented him on the impressive bookcase he owned and those who asked him if he had read all those books.
For Eco, the library was not a “display of culture” (as Taleb states in his spectacular “Black Swan”) but a research tool, something that reminds us that “we don’t know everything”.
It is as if “unread” books are much more important than those we know or think we know. Now to get out of this intellectual and “complex” whirlwind we just need to think of something very simple:
If you can’t do a certain thing, you don’t even have the tools to assess your skills in that field. As in the example of swimming used in the episode, if you don’t know how to swim how do you evaluate the performance of a swimmer?
You can certainly be fascinated by Federica Pellegrini’s exploits, you can appreciate the elegance of a dive, but if you’ve never done it, you can understand only a small part of that gesture.
Simulation and learning
As we have seen on several occasions, our brain moves in the environment through a series of simulations, it tries to understand the world through the continuous construction of “virtual” scenarios.
Partly because it lacks the elements and partly because it is a great way to learn. We psychologists first saw this with the vicarious learning of Bandura, the famous modeling.
And then with the “embodied simulation” of mirror neurons. You see a certain athletic gesture and your body tells you: “I could do it too” because in its simulation it is able to do it.
This facilitates learning on the one hand and on the other it deceives you that you know how to do things. And in a world where we have many “virtual simulations” available, it is easier to delude ourselves that we know how to do what we observe.
A striking example is what you are reading right now: people see that one opens a blog, a youtube channel and thinks: “but does that publish those things? I would also be able to do it ”… then try it
The illusion of knowledge motivates us
As you know the web gives us enormous opportunities, anyone can open a blog, a youtube channel or any other social network and start posting. And observing others think it is possible to do so.
It is precisely through this simulation that one can feel motivated to know how to do this thing, don’t think: I have to do 10,000 things before I can useEcology
A striking example of complexity is ecology. This subject as a study of the environment is over 1 century old, but only today we hear so much about “climate change”, because its effects have become evident.
An “ecological” thought is not only linked to the environment but is also linked to the complex web of interconnections that exist within it, as Gragory Bateson elegantly demonstrated in his masterpiece: “towards an ecology of the mind”.
Having a “systemic look”, as Fritjof Capra would say, is not an intellectual habit but is the only way to be able to understand the reality that surrounds us. Otherwise, doctors continue to ignore engineering and vice versa.
Knowing that the world is complex is the real key to understand it, to try to understand all the phenomena that happen there, even and above all those that interest us, that is the psychological ones.
Our brain is so in love with simplicity that it builds preferential ways when it finds it. This is the effect of cognitive fluency.
Everything that we can understand easily and without too much effort also tends to like us more, because it allows us to maintain the illusion of knowledge without wasting “cognitive” energy.
On the one hand it is very useful not to have to “reinvent the wheel” every day, but on the other hand it can become dangerous especially when we face things we do not yet know.
This is a bilateral paradox, because if on the one hand we tend to appreciate what is “fluid” for us, we do not realize on the other hand that this fluidity changes from person to person.
Returning to our doctor and our engineer, it will be easier for a doctor to interpret the world from a biological point of view, while for an engineer it will be easier to interpret the world from the point of view of “physics” and “mechanics”.
The illusion of knowledge
The illusion of knowledge is the name I took from the research of Steven Sloman and Philip Brenbach who also published a text in Italian with the same name (you can find it in the link above).
As described in the episode, the two “cognitive scientists” have carried out some really interesting studies, some so banal as to be unsettling and self-evident.
Like that of the bicycle I described to you, where subjects were invited to complete some drawings of incomplete bicycles. They also did it with tools we use every day such as “pens”.
Showing that we are really immersed in a sort of “artificial unconscious” (Legrenzi and Humility) that corresponds to that theory of “black boxes”: we live immersed in things we do not know.
The advent of digital has worsened this feeling, the problem is that some are completely unaware of this, and indeed believe they know much more than they really know.
Just like people who have been asked to describe the simple operation of a pen or to complete the stylized drawing of a bicycle, without a chain or pedals.
Black and white
The “black / white” thought is among the most fascinating of all: because it fully reflects the illusion of knowledge but in certain contexts it is essential to delimit the field of knowledge.
Not being able to know everything we have to impose limits and affirm that a certain thing is such only if it respects certain parameters. Otherwise everything is everything… because our systemic network shows us that everything “is connected with everything”.
This shouldn’t discourage us but simply open our eyes to a much more complex and fascinating world. This is not about magic or newage, like in the video you saw above.
The fact that Capra is appreciated in such circles does not mean that he is a kind of holy man, far from it. Because often in “spiritual” environments we try to explain things from many points of view.
However, looking for explanations in the soul when it would be enough to know better the complexity of nature is another cognitive error. It is no coincidence that the ancients thought that it was gods who sent rain and lightning.
In short, as you can see it is much more complex than that … for today I stop because I could go on for a long time, let’s continue our discussion in the Qde