Bring Up Sight—How Do You See

We, as humans, often take for granted how much we rely on vision to gather critical pieces of information. Information that allows us to properly comprehend all that is happening in the world we’re in. Neglecting its importance is a complete oversight, pun intended. We rely so much on what we see to determine our reality that we regularly fall into the trap of optical illusions (stay tuned for an upcoming post). Then, questioning what we see becomes primordial. But first, we need to establish how this sense works. It will come to you as no surprise to learn that the organs responsible for sight are the eyes. Those delicate globular organs are the product of many parts, all working together, enabling us to detect light and its many properties.

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Light is a form of energy called electromagnetic radiation that travels as waves. Only a portion of electromagnetic radiation, found within the visible light spectrum, can be seen through our eyes. This spectrum includes any wavelengths between 400 nm and 700 nm, 400 nm associated with blue light and 700 nm with red. Wavelengths certainly exist beyond that range, but we are unfortunately unable to see them through our naked eyes. We consider any shorter wavelengths (10–400 nm) to produce ultraviolet lights and longer waves (700 nm-1mm) to generate infrared lights. All of the invisible light might escape our natural perception, but beware that it is far from useless.

We deal with those wavelengths every day. Ultraviolet is an aseptic agent (kills bacteria), but it is also used as a tanning agent for tanning beds. Actually, there is a logic behind this second example. The Sun is a massive emitter of ultraviolet light, commonly referred to as UV light (UV). It is that invisible light that is responsible for you getting that sun-kissed skin you so desire. However, that same light is also what is responsible for so many new cases of skin cancer. The risk associated with UV light exposure is the reason why we all need to protect against it. We must continue or, at the very least, start using proper sun-blocking agents like sunscreens covering against both UVA (UV type-A) and UVB (UV type-B).

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We can find infrared light often used in night-vision cameras, remote controllers, infrared astronomy and fibre-optic cables. These application examples might make it sound as if infrared was totally harmless, but it is sadly not. Infrared is responsible for the greenhouse effect, i.e. getting the Earth warmer than it should or would be. The greenhouse gases are efficiently trapping infrared light near the Earth’s surface. The more greenhouse gases (like carbon dioxide, nitrous oxide, methane and ozone) we release, the greater the heat produced through the greenhouse effect will be.

On a more positive note, let’s come back to how our eyes can perceive all that visible light. When light reflects back into our eyes, it first hits the cornea. It is a transparent part of our eyes forming a dome, which serves as the primary and most important focusing power. However, despite being so impressive, it lacks something that only the lens has, an adjustable focus. The cornea focuses on the pupil (the dark spot at the centre of our eyes). To control the amount of light passing through the pupil, the iris (the colourful circle in our eyes) will stretch to let more light in (for darker conditions) or shrink to block some (for lighter conditions).

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For the next part, if we try keeping things as simple as possible, we may say that the light goes directly to the retina. The retina is a light-sensitive layer of tissue containing photoreceptors known as cones and rods. The cones are wavelength-sensitive which means that they are in charge of colour perceptions. They are also responsible for high acuity vision, and they work best in well-lit conditions. In obscure conditions, the rods are particularly helpful as they still can provide us with a black and white vision. Once the photoreceptors detect lights, it triggers an electrical signal which will travel to the brain via the optic nerves.

So, as I said previously, this is a simplified version, so let’s complicate the matter a little more. Before reaching the retina, the light passes through a structure called the lens, which converges (or focuses) the light on the retina by refracting it. The lens connects to suspensory ligaments that can control its curvature changing its focal range. This process is called accommodation and leads to the creation of a sharper image. However, once the light gets past the lens, it is not quite yet at the retina. The light has to swim through a transparent liquid, the vitreous humour. This substance is helping to maintain the shape of the eye and protects against sudden shocks. Now that the light has finally reached the retina, it must hit a particular spot to produce a crisp image, and that spot is called the macula. In the absence of an eye disorder, the lenses will manage to focus an image onto the fovea found in the macula. The fovea is the region of the retina where the cones are at their highest confluence. Finally, there is one last eye part, and it doesn’t seem to provide as much value for sight. However, it appears to be very precious for communication. That part is the sclera, the white part of our eyes.

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All these parts work in unison as do musical instruments of a symphony. Without one, the others cannot function appropriately. For its maintenance, the eye has a cleaning and lubricating agent mostly referred to as tears. Yet sometimes, tears are not sufficient to resolve some situations we may face. It is unquestionably the case of people affected by eye disorders, like nearsightedness (myopia) or far-sightedness (hypermetropia). These disorders commonly occur when the axial length of the eye is respectively too long or too short. Nonetheless, they could also result from an anomaly regarding the lenses’ shape or failure to produce suitable accommodation.

These two disorders are inducing refractive errors. Yet, they are not the only ones; presbyopia and astigmatism also produce refractive errors. Presbyopia mainly occurs when ageing, the lenses weaken and are thus less able to adjust or accommodate. As for astigmatism, I can speak from my own experience. I was first diagnosed with astigmatism three years ago. If we could all omit this slight astigmatism, my vision would be pretty much 20/20; I have no sign of near or far-sightedness, and my eyeballs are neither elongated nor short. Yet my sight is somehow blurred when I am looking from both close and far distances. This blurriness causes strain to my eye, especially when I have to focus heavily on something. My main occupation at present is reading. And thus, I am regularly using prescription reading glasses for extended reading. It is the only moment I need glasses. That blurriness comes from light not being evenly distributed on the retina. This situation can arise from an issue with the lenses or the cornea.

Luckily for us, all these disorders have the potential to be treated through laser surgery. Even though I have decided that it wasn’t necessary as my current glasses suffice me. I still keep in mind that although laser surgeries are becoming safer and safer, there will still forever remain some risks. With reading glasses, those risks naturally don’t exist. Let’s say that I’m not against reconsidering this option if my situation worsens; it is still an exceedingly attractive procedure. But right now, I have honestly no incentive to go along with it. What about you? If you had the opportunity to opt for laser surgery, would you do it?

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I thank you infinitely for reading this post and if you would like to know more about the mysteries that surround us, please join my subscription list to keep up with my newest content. If you have any questions, please add them to the comment section and I’ll make sure to answer as soon as humanly possible.

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Bring Up Biophilia—What makes us particularly attracted to nature

No one can dismiss the amazing feeling we get after spending some time in nature. We instantly feel relaxed and reinvigorated. Some might attribute this effect to time spent far away from work, and even though they could be correct, it is not the whole picture. Biophilia is a relatively new concept that brought the…

Bring Up Blood—How our oxygen gets carried throughout our body

Good evening my dearest followers, Please, take a moment to enjoy this excerpt for my newest post (Bring Up Blood). We could most certainly not live without blood. It is absolutely essential for the survival of our most distant limbs and organs. Even though almost all of our respiration is thanks to our respiratory organs,…

Bring Up Hearing—Where is this sound coming from

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The type of stimulus that first recruits my awareness in the morning is most probably auditory. The sound may be coming from outside, like bird songs, or it could be coming from indoors, like my scheduled alarms. It certainly sounds more pleasant to be awakened by the tweeting of the birds, but living in Montréal, hearing the rumblings of heavy machinery is definitely more likely, which is sincerely irritating. This observation raises a particular question about the pleasantness of sounds and its origin. To answer the how and where its pleasantness comes from, we must know the differences between music and noise. However, it may not be as straightforward a question as it may seem.

The nature of sound is quite interesting as it doesn’t have any material constituents. Nobody was ever able to grab sound, to see sound or to taste sound. We cannot do any of those because a sound is a product of vibrations that spread through the air (or water) as acoustic waves. Depending on the properties displayed by the acoustic waves, the sound can be perceived differently. On the one hand, we can interpret a sound to have different levels of loudness which is attributed, in most parts, to the amplitude of the waves. The greater the amplitude (the height from the resting point to the top of the wave), the louder we recognize the sound to be. On the other hand, a sound can also have a different pitch depending on the specific period, frequency and wavelength it displays.

Acoustic waves generally follow the pattern dictated by sinusoidal functions, which we probably all encountered at some point in High School. For acoustic waves, the amplitude -determined by the height between the maximum and the x-axis- is still conserved. We only need one tiny adjustment; the x-axis now becomes known as the resting point. A period becomes the time it takes for the sound to complete its cycle. The frequency becomes the number of cycles completed within a specific time, which we typically calculate in Hertz (Hz; cycle/second). The wavelength is then the amount of distance sound can travel per period. They (all three) remain closely related to one another; the frequency is inversely proportional to both the period and the wavelength.

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These properties mean that the longer the wavelength (smaller Hz) is, the lower the frequency becomes. And as for the pitch, the inverse is also true. Although, there exist limitations to this observation. Namely, the limit of our human ear. They only possess the ability to detect sound within the range of 64 Hz to 23 kHz. However, some animals can perceive sound in much greater ranges than we can. Dogs are one of these animals with a hearing capacity between 67 Hz to 45 kHz. Nevertheless, cats take the lead here with their remarkable hearing sensibility ranging from 45 Hz to 67 kHz. This characteristic may describe their incredible success at hunting little prey such as rodents, which can emit sound as high as 100 kHz.

Depending on what the sound passes through, the speed and its direction can and will vary. Water, being thicker than air, will most definitely slow down sounds and redirect at a much greater angle than what we can observe with air. This redirection is also called refraction, which is the same phenomenon that is responsible for the shift of the image when seeing an object immersed in water. If, for whatever reason, you absolutely have no idea of what I am referring to, try this: take a transparent glass of water and partly submerged an opaque object in it (could be anything). You can see that the object seems broken when it passes through water, and that is refraction.

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Even though there are many properties characterizing sound, the ear is principally reactive to one, frequency. Amplitude will only play a background role to infer loudness to the sound. Our ear, which is our hearing organ, seems particularly attuned to pitch and loudness. As sounds are created, through the contact of objects causing vibration, it produces the acoustic waves as mentioned earlier. Upon hitting the auricle, the sound will be amplified and modulated before reaching the eardrum. The vibration, amplification and modulation create a chain reaction in the middle ear, which activates the ossicles (Malleus, Incus, and Stapes). The ossicles will then transmit the sound wave to the cochlea in the inner ear. In the cochlea, we can find plenty of hearing nerves, which connect to the brain. Once at the brain, the signal becomes interpreted to allow identification, classification and interpretation of the sounds.

It is the brain that is responsible for determining the pleasant nature of the sound we hear. Some people are affected by a condition that renders them unable to enjoy or derive any pleasure from music. This condition is known as musical anhedonia. It is a neurological condition caused by reduced connectivity in subcortical regions related to reward. Although these people might not be able to enjoy music, they can most definitely identify it, unlike those suffering from music agnosia. Despite their ability to hear, the latter cannot even tell the difference between music and noise. Individuals typically acquire this condition following an injury to at least one of the temporal lobes or after a unilateral stroke. These two conditions splendidly reveal the importance of the brain’s interpretation role in the perception of music.

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There is one more aspect of sound that I haven’t introduced yet: timbre. This term is often replaced by “sound quality” as it refers to the nature and distinctiveness of a sound, in other words, the pattern of harmonics. For instance, a violin will never sound exactly like a piano, even though you decide to play the same note at the same loudness level. Now, despite having described all these aspects and properties of sound, we still fall short when it comes to explaining where the pleasantness of music originates. However, what we have discussed so far was more related to sound itself and not music. What makes music is its rhythm or tempo, which creates sound arrangements through time, that can either be pleasing or not. When considering music perception, rhythm and pitch are the most central aspects involved.

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Now that I have introduced rhythm, we can start approaching closer to an answer. There are many factors involved; familiarity, distortion and reverb. As a general rule, we prefer sounds and/or patterns of sound that we are more familiar with; the ones we heard before. Usually, music acquires its different alluring attributes over relatively long periods. Music is pretty conservative as a general rule. However, beyond familiarity, there are distortion and reverb, each responsible for some aspect of pleasantness. Distortion comes from making the tone of the sound imperfect by changing its original form. Reverb is pretty much like echo, but instead of having the sound coming back to you in two parts, it comes back to you almost immediately. Although, not fast enough for merging with the original sound. The result becomes a continuation of the sound. We can often witness reverb in churches or even (ahem!) the shower. Reverb partly explains why it’s so delightful to hear ourselves signing in the shower. Yet, I cannot say I do much of that; my showers are always too short for that. How about you?

I thank you infinitely for reading this post and if you would like to know more about the mysteries that surround us, please join my subscription list to keep up with my newest content. If you have any questions, please add them to the comment section and I’ll make sure to answer as soon as humanly possible.

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Bring Up Tattoo—How it can be possible to mark our skin permanently

Not all appearance alterations are created equal; some may be more short-lived and others more permanent. If you think of tattoos, they mostly belong to the second category. So thinking carefully about certain aspects of the tattoo becomes imperative. Things like the symbolism or the artistry behind your new piece shouldn’t be random. Choosing a…

Bring Up Grad School—What Is the Reality Behind Higher Education

For people who want to pursue studies after completing high school, university studies may look very attractive. So, undergraduate studies may lead to graduate studies. However, undergraduate studies are not the same as graduate studies. The latter is not only more complicated, but it is also very different. First of all, contrary to your undergrad,…