OPTICAL ILLUSIONS: A DEFECT OF HUMAN COGNITION; OR IT’S US WHO REFUSED TO SEE WHAT WE WISH NOT TO?
The eyes should not be held accountable for the countless times we got deceived by the illusions.
In our previous article on time illusions [1], we have given a brief explanation on the process of how human cognition processes the information received by our senses (or, in other words, the stimuli for the environment). From a purely physical perspective, cognition is a flawed system. It would inevitably subject to “lags”, as a existent latency is required for the stimuli to appear, then get perceived by our senses, and after that undergo the extremely sophisticated processes of the brain for processing these data, until they are finally outputted in the form of a full picture that is our perception of the surrounding environment.
To compensate for the latency and the incomplete information, our cognitive system has granted itself with the abilities to predict the developments of the phenomena, to insert/omit data to form the most completed and seamless “reality” that it could possibly reproduce. But even then, it’s just physically impossible for this system to make up entirely for these inherent weaknesses, and we have to live with the truth that the reality reproduced by our cognition will always be , by definition, a pseudo-reality.
At least in terms of visual perception, what we see “at present time” that happened a few milliseconds ago in reality. Even when this latency is greatly marginal and the functionality of human eyes is not much different from that of cameras, it could still never reflect entirely correctly what is shown before the retina, and thus make us prone to get confused by what we see. The flash-lag effect, the “movements” of still picture (a list of all optical illusions to be mentioned in this article from this point onward will be made available in the comment section), or the debates how the black-blue/gold-white dress that went viral on the Internet a few of years ago [2] are some of the examples to show us how easily deceptible our eyes can sometimes be.
Or, to word it more precisely — it’s the evidence to help depict the incompleteness of the cognitive system that is controlling all and every activity of our bodies.
1. Eyes never lie.
Visual or optical illusions include numerous types with just as diverse characteristics, but then can be generally defined as the misinterpretation of the information that the eyes perceive, to form an incorrect perception of the reality that we see [3]. With the exception of the illusions that are actually caused by the laws of physics, such as when the spoon dipped halfway into water looks like it “splitted”, or the mirage phenomenon caused by the light refraction between layers of air that are heated up to different temperature [4]; in most cases, optical illusions are caused intentionally by elaborately arranged images.
The arrangement of details, colors, shadowing direction, movement direction, … in a special case can make us perceive straight lines as curved, unparalleled or shorter/longer than one another even when they are parallel and equal in length. A lot of illusions can even change the color, shape or movement direction of an object from how they are initially perceived.
(Note: Additionally, illusion should also not be confused with hallucination, as the latter refers to the perception that happens even when there’s no stimuli, meaning that we are perceiving things that’s non-existent [5]. Illusion: A → A’; Hallucination: nothing → A.)
As for the cause, even when the process of sense-data processing naturally receives a degree of intervention from the general cognitive system, the optical illusions are often caused by a conglomeration of factors that far beyond just the brain’s mechanisms of information latency or automatic insertion.
For example, as our brain cannot in-one-step perceive the actual colors and brightness an object A; but instead have to perceive it by comparing these attributes of object A with other objects B, C, D… nearby, this can lead to an optical illusion of different shades of grey between the actually similarly-colored squares on a chess board (see the comment section).
In the case of the Zöllner illusion, where a series of parallel, black diagonal lines which are crossed with short, repeating lines can give the impression that they are in disorder; even when in reality they are perfectly parallel. The reason is that the angles created by the shorter lines crossing the long lines will create the impression of a 3D depth, which causes beholders to mistake them with an arrangement of interwoven lines that are running toward the distance. This illusion has shown use that the arrangement of background details (in this case, the short crossing lines) can actually distort our perception of the foreground objects (the parallel lines) in the picture [6].
Or in case of apparent motion, or sometimes called the ‘snake illusion’, the ever so slight “jiggling” of shapes such as circles or vortexes were actually the results of our eyes’ constant movements so fast we cannot at all perceive (saccade). Within 1 seconds, the eyes would move lots and lots times toward many different directions to “take photoshoot” of the many jigsaw pieces of the picture and then put them together in one single frame. This constant movement in cahoots with the curves or any other type of confusing patterns have caused the illusion of non-existent rotational motion [7].
On a more fundamental level, we might as take a closer look into the biological structure and the functionality of the human eyes to justify its deceptibility. The 1981’s Nobel Physiology or Medicine was awarded to David Hubel and Torsten Wiesel for their discoveries concerning information processing in the visual system. As it turns out, the way the neurons ``see” things were way more complex than we previously imagined. Each specific type of information, namely the colors, shapes, movements, and patterns of an imagine received by the cornea were actually not simultaneously processed; but instead the responsibilities to handle them were divided between different types of neural cells. With MRI scans, it had been discovered that when people see illusions, there actually appeared some type of competition among these neurons for transmission of information, and this competition in turns affected our cognition and thus gave us wrong impressions [8].
(Note: If you feel the need to look into more types of illusions, then the 800-page The Oxford Compendium of Visual Illusions” from Oxford University Press might just be right book for you [9].)
To put it simply the eyes should not be held accountable for the countless times we got deceived by the illusions. It was simply how these so-called “windows to the soul” and the visual data processing system behind them meant to operate.
Essentially, the factors down under the unconscious level or the build-in mechanisms boast great influence in the process; but the problem is we cannot really notice their influence during our daily activities. Even our subjective thoughts and behaviors, which were always thought to be entirely and undisputedly under the command of intelligence and cognition; could still actually be (and, in fact, ever so predominantly so) directed by cognitive biases. And it is also worth mentioning again, that the processing of sense data, unfortunately, is processed by this lag-prone, like-to-speculate set of hardware that is our brain; and thus give us all the more reasons to take errors as inevitable.
However, these illusions would still be considered much less harmless than the physics-induced illusions that can cause asphalt roads look dripping wet to drivers on hot days, cause the desert-stranded explorers to exhaust themselves chasing a non-existent oasis, or also might as well have been the culprit of the historical Titanic shipwreck [10]. In the meantime, the illusions caused by cognitive errors are being used as a medium for the research of visual information processing [11]. In case of rubber-hand illusion [12], the much “illusory” perception of the body were also employed as a therapy for OCD [13]. And even if it isn’t so useful, we could still take it as a pretty interesting and entertaining “magic trick”.
But the question is, are these illusions purely just the games of the mind?
It should be noted that, we are more or less one of the most completed creations in the biosphere, which have received countless upgrades and patches from the renownedly ingenious manufacturer that is Evolution. If such an important mechanism of cognition and sense information processing are designed with so many grave flaws just so that our mind can entertain itself, then we probably were not that fit for survival and should have gone extinct long along before we managed to reach this age where we have the free time to sit at the computer and search for these mind-twisting images on the Internet.
2. So who is deceiving whom?
A few milliseconds while may not matter as much for humans; but is actually that life-or-death-matter period of time needed for the flies to change their flying courses to save themselves from the wraith of a flyswatter or anything similar [14]. Thanks to the double compound eyes consisting of thousands of receptors that more or less function like tiny eyes, they can process high speed movements and retain a broader visual field (Flies: 1 — Captain of the Titanic: 0).
However, that doesn’t actually help the flies to not get tricked by the apparent movement illusion [15] (Flies: 0 — Captain of the Titanic: 0).
And as it turns out, it wasn’t just the flies or our primate relatives to get mind f*cked by the elaborately arranged images like we did [16]; being fooled by optical illusions are much more of common place for the species in the world of animals [17]. Even the rates — the most battle-hardened veterans among lab animals; were also spooked in rubber-hand illusion experiences [18]. Even more fascinatingly, when programmed to process visual data through a process that simulate that of human brain’s visual data processing, computers were also ended up getting tricked by simple illusions [19]. And another something so incredible but yet so commonly found is that even when we have been previously educated about an illusion, we could still never find a way to tell the brain to stop getting tricked by that illusion [20].
Therefore, the vulnerability to optical illusions seems to be the general trend in the biological world. To a certain extent, the existence of optical illusions can more or less be considered a secondary state of normalcy. For example, people with autism, regardless of their age, are actually a lot less likely to suffer the cognitive errors that are optical illusions than normal people, so much that optical illusions are actually employed as a mean for diagnosis of this syndrome [21].
This indicates that, from the perspective of evolution, the deceivability of our visual system or the inherent so-called “flaws” of the cognitive system in general, was not by any mean an obsolete feature or a defect overlooked by evolution; it might as well play a crucial role in helping living species to survive better.
Take the attention mechanism for example: It does not work like a spotlight on stage that turns toward and highlights the things that pique our interest. The secret actually lies in how it manages unlit area. When it wishes to focus on a subject, instead of doing the highly-laborious task that is highlighting the said subject, our cognition would look to blur everything else around the subject, which helps the brain’s information processing to be much more energy efficient [22]. While this mechanism does create loopholes for us to overlook some of the changes around us (changes blindness [23]); it also keeps us from exhausting our resources trying to pay attention to all and everything.
Our ability to perceive 3D depth on a 2D panel was actually also a type of Illusion. This perception stemmed from our ability to perceive the shadowing, in combination with another more fundamental cause, which is our visual nervous system’s priorities in the extracting and process of objects’ color information [24]. These priorities help us quickly and easily group up areas that are similarly colored and distinguish them with other environmental factors with different color.
For example, imagine when there’s a lion hiding behind a green shrub, prowling for a prey. We will be able to immediately notice something’s out of irregular as we see yellow spots in the midst of a green background. But how did our brain make it so that those few yellow dots, even though they seem so insignificant in terms of presence, can actually ring the alarm in our head? This is where the ingenuity of the brain is showcased, as it groups the yellow dots into a single entity, and thus provides additional information based on the limited amount of data on the limited information that it’s provided with. As a result, as it encounters these seemingly-so-insignificant gold spots, our brain will start to pinpoint and make speculation on the shape of the thing that is being covered by the shrub. And as an image incomplete but yet recognizable of the predator with a characteristic golden fur comes to mind, it will also be when our brain starts to scream: “Run! Now!”.
Taking advantage of the fact that color is the thing that “meets the eyes” first, many species of animal have developed from themselves a disguise mechanism called “countershading”. Specifically, these animals would wear darker color on the back and brighter color on front, to generate a high level of contrast. And, since we distinguish objects and environment around them by color contrast, if the contrast exists on the animal’s body itself, the brain would confuse a part of that body with a part of the surrounding [25].
For example, in a marine environment, from a bird-eye perspective, the dark-colored back of sharks will blend in with the dark-colored seabed. Meanwhile, from underneath, their bright-colored bellies would be of a color shade much closely resembling that of a sunlit sea surface. From the perspective of something on the shore, this contrast color scheme also creates the illusion that these animals and their shadows on the bottom are in the same block, and thus actually makes them look flatter (3D → 2D) and, in turns, less noticeable to the prey. Contrary to the “easy prey” species which would look to hide themselves away the best they can, the animals which are highly proficient at defending themselves like the skunks or honey badgers are actually more of the “showoff” types. By employing a contrast setting that is the reversed of the previously discussed color scheme (known as reverse countershading), where the back is colored bright and the belly is colored dark, they make their presence more clearly recognizable as a warning to shoo the predators away.
What’s more, illusion is also a highly effective tool to find mating partners, especially among the species of birds. The colorful feather-tails of the male great argus pheasants are decorated with big, round, disk-shaped patterns called the eye spots. In their courtship “dance”, the upright-raised tail feathers along with the eye spots that are lighter colored on the top half darker colored on the bottom half turn these disks into the 3D illusion of sparkling metal balls. And, according to the aesthetics of birds, those resemble the beauty of jewelleries [26]. For the case of the bowerbirds, as a female enter a nest elaborately constructed by a male, that takes the the form of a cylinder, the perspective of the female will create an illusion that the ornaments at the back of the tunnel, (small pebbles or pieces of bone) were actually petite and uniform. The visual build of the male would thus be slightly inflated from how it is in reality, and that in turns give them a better chance at winning the female’s heart [27]. Also looking to take advantage of illusions to make themselves look bigger , the male fiddler crabs prove themselves to be a level above as they learnt to employ the Ebbinghaus effects: they would intentionally walk alongside the individuals smaller than them so can become bigger in the eyes of the females [28].
So, to summarize, the world as we perceive, in a sense, may as well be a giant conglomeration of illusions. Both the reality and information preexisting in the mind, a little bit from each is used by the brain as ingredients to cook up a full picture that is our perception of the world around us. And we have been and will be spending our lives living within it. However, this truth is largely unknown, people would still take illusions as something “out of ordinary”, even when the “ordinary world” that we are perceiving have by itself already consist of innumerable illusions. Which means, if there actually existed a button that would turn off all the illusions when we press it, everything would get unimaginably horrible rather than better as we may think.
And as our cognition plays a tremendous role in the generation of the reality that we perceive, whatever affects it would also in turn affect the pseudo-reality generated by it. And it’s not just biological factors: Social factors can also very much significantly impact on these illusions.
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