How Do Humans See?

By now readers have figured out how much I love etymology, the study of word origin. I often start my research explorations by making sure I understand the words surrounding a topic, and today is one of those days. Where did the word “see” come from? And the noun “vision”? And the word eyesight?

See comes from the Old English seon “to see, look, behold; observe, perceive, understand; experience, visit, inspect”. That definition of see hasn’t really changed much over time.

The word vision, however, has changed thanks to science and our understanding of the brain. Here’s the etymology of vision.

c. 1300, “something seen in the imagination or in the supernatural,” from Anglo-French visioun, Old French vision “presence, sight; view, look, appearance; dream, supernatural sight” (12c.), from Latin visionem (nominative visio) “act of seeing, sight, thing seen,” noun of action from past participle stem of videre “to see,”

Eyesight, a compound word, traces its roots back to about 1200 and means “sense of sight, capacity for seeing,” 

So what really is the difference between vision and seeing, or eyesight? In her book, The Hidden Link Between Vision and Learning, author Wendy Beth Rosen uses two sentences to help us understand the difference between eyesight and vision.

Eyesight is the physiological ability to receive input through the eyes. Vision is the ability to understand what the input is.

Wendy Beth Rosen, the Hidden Link Between Vision and Learning, p. 1

People think we see with our eyes. We actually see with our brains; the eyes are the hunters and gathers of the process. This graphic from the Thruhlsen-Marmor Museum of the Eye explains the process quite simply.

Consequently, how people take in the world is essentially a two-step process involving the eyes and the brain. And here’s where I turn the reader’s long held notion of “perfect” vision upside down. Just because your eye exam results tell you you have 20/20 vision, doesn’t mean your brain has great reception from your eyes so that you see well. I have had 20/20 vision for much of my life; but, the strabismus I was born with, while cosmetically corrected, was not corrected so that my eyes worked together to gather information for my brain. (You can catch up on that discussion here.)

What actually gets measured during a routing eye exam–or even the vision testing in the school nurse’s office–is visual acuity. Rosen writes, visual acuity can be defined as how clear symbols or objects look at a certain distance. (p. 3) That visual acuity is measured using a Snellin Chart. But that’s all the 158-year old Snellin chart measures; it doesn’t measure how your eyes send information to the brain.

Having 20/20 vision means that we can see clearly at 20 feet what is supposed to be seen clearly at this distance. If you’re told that you have, for example, 20/26 vision, it means that you have to be 20 feet from what a person with normal vision can see at 60 feet.

Wendy Beth Rosen, the Hidden Link Between Vision and Learning, p. 5

You can read more about 20/20 vision here.

So seeing clearly, is not necessarily seeing well. Visual acuity is just one small piece of the complicated process Rosen labels visual skills. And visual skills help a person navigate in the world. From depth perception, to peripheral vision, to knowing where one is in time and space, that’s all a part of an intact vision system, of which the hunting and gathering of the eyes is an important part; the eyes transmit the information to the brain.

To fully grasp the profound tole that vision plays in our day-to-day activities, consider this: 80 percent of the neurological pathways in the brain connect with the visual system.

Wendy Beth Rosen, the Hidden Link Between Vision and Learning, p. 12

People write dissertations on topics like this; that’s not my intention today. What I really want the reader to understand is “seeing” is a very complicated and critical process for human beings and other creatures. And, how one’s sees, or doesn’t see, can make a big difference in life, especially in learning.

Want to read more about the Science of Vision? Here’s a reference list:

From the Dana Foundation, a private philanthropic organization dedicated to advancing understanding about the brain in health and disease through research grants and public outreach.

Kahn Academy, the people who can make the complex understandable with online lessons! Use the search bar to find all sorts of lessons on the eyes, the brain and vision.

Thruhlsen-Marmor Museum of the Eye has an array of offerings for learners of all ages. Explore.

See you soon! (Ever think about that sentence?)

Picture of a Congo African Grey parrot
33-year old Toby, a Congo African grey parrot. Yes, parrots have eyes on the sides of their heads! That’s another story!

One thought on “How Do Humans See?

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