To use the analogy of a computer, our senses are the hardware, our culture is the software and our mind is the operating system, mediating the two. From an anatomical standpoint, humans have not changed for about 200,000 years. For most people, our senses are unchanging biological facts, although we may lose our senses partially or completely due to accidents or through plain senescence. Senses form the connection between our internal and external worlds. Without the ability to see, hear, touch, smell, and taste, our mind is cut off from our environment, which causes a break in the feedback loop for us to perceive our actions. Imagine the simple task of eating using a spoon without any of your senses — not only would the task be impossible to accomplish, but the premise of taking any form of action would also be completely absurd since there is no experience to begin with. This shows how fundamental our senses are to our being. 

While our senses are reliable enough for us to conduct our everyday lives, we know that they are by no means transparent communicators of objective reality. Perceptual illusions show that our senses can often be fooled. (It is important to note here that perception is not exclusively within the domain of senses but emerges from the interaction between senses and the mind.) In 2015, “the dress” made huge waves around the internet, dividing netizens into two camps (as the internet does). Half of the internet argued that the image depicted a black and blue dress while the other believed that it was white and gold. (Spoiler alert: it is the former.) In 2018, a similar meme rocked the online world. Instead of an optical illusion, it was an auditory one, known as “Yanny or Laurel”. It got the internet similarly divided. These illusions are not new, however, and are generally known as ambiguous images. The classic “rabbit-duck” illusion was published in a German humor magazine in 1892.

Our vision is the most studied among the senses, possibly due to humans’ outsized reliance on sight. This has led to quite an exhaustive list of optical illusions over the years. Josef Albers, a renowned artist-educator, published his insights on color in his seminal book Interaction of Color in 1963. His theories are inspired by Gestalt psychology while he was at the now-legendary Bauhaus. When I first read it in art school in 2013, I was struck by how timeless it was. Within the book, Albers discussed how color “is almost never seen as it really is” and that “color deceives continually.” Through visual examples, he shows the phenomenon of simultaneous contrast, in which an identical color is perceived as different when placed within different colored backgrounds. Besides color and tone, our eyes can also misperceive relative sizes; examples of this include the Ebbinghaus illusion and Shepard tables. 

Besides perceptual effects of ambiguity and relativity, our perception can also be altered. A few years ago, I tried a miracle berry, which is a fruit that contains the taste modifier miraculin. Eating this berry causes sour foods to taste sweet. Hallucinogens contain psychoactive compounds that cause people to have perceptions in the absence of real external stimuli (i.e. see objects that do not actually exist). Such perceptual alterations may also be a result of illness or physiological processes and responses. Hallucination is a known symptom of Parkinson’s disease and can also be experienced by people right before falling asleep, a phenomenon known as hypnagogia. Research has also shown that our perception of time can change when we experience danger, possibly due to the adrenaline rush caused by the fight-or-flight response. In popular culture, this is sometimes called the slow-mo effect (a metaphor borrowed from video editing).

In some scenarios, one sense can override another. I got to know about the McGurk effect when I was taking a cognitive science class at college. I encourage you to try it for yourself before you continue reading. Go to this YouTube video, click play but do not watch the video. Instead, just listen to the sound and try to identify the sound that is being spoken. (The video is about 1-minute long.) Now, play the video again. This time, listen to the sound while watching the video. You may notice that the sound seems to have conformed to the mouth shape of the person who is speaking. This is to say, the sound that we perceive has changed due to a visual inconsistency. In this case, our sight has overridden our hearing to produce a different perception of the same sound. Another instance of this is best summed up in a well-known adage among chefs, that “we eat first with our eyes”, first coined by first-century Roman gourmand Apicius. Research shows that the manner in which food is arranged visually affects our perception of flavor and can cause people to alter their food choices. Sometimes, even different aspects of the same sense can override each other. This is demonstrated by the Stroop effect, in which the name of a color like “green” is colored with another color, like red. We take much longer to name the colors of these words, as there is incongruent perceptual information.

Beyond the tendency for illusory perceptions, we know that our senses are simply unable to perceive otherwise undetectable phenomena, which can now be measured using scientific instruments. Our eyes can only observe a small fraction of the electromagnetic spectrum. Our ears can perceive only frequencies between 20Hz and 20 kHz. Our sense of smell is deficient compared to dogs, whose incredible noses help humans with law enforcement and even perhaps identify COVID-19. The limitations of our senses lead us to an even bigger question — are there phenomena that we just cannot know simply because we have no way of detecting its existence?

Writer’s note: this is part one of a three-part essay. Click here for part two.