Visualization is the collection of biological processes that transform light waves into eyesight. Visualization isn’t something that only people do. Some of the simplest animals, like the larvae of sponges and jellyfish, have light-sensitive cells that help them respond to their environment. More complex animals like birds and mammals have sophisticated vision systems that help them hunt, feed, find mates and flee from predators.
For this article, we’ll stick to human visualization, which has four key components:
Optical mechanisms in the eye
Visual centers in the brain
Let’s take a quick look at how these factors come together to create visualization.
Visible light: waves of radiation that produce photons
When you hear the word radiation, you might think of a cancer treatment or the damage from an atomic blast. But radiation also comes from electromagnetic sources like the sun and the stars.
Electromagnetic radiation travels in waves that rise and fall like the movement of water in the ocean. The wavelength measures the wave’s size. The electromagnetic spectrum is every known wavelength, from smallest to largest.
The human vision system cannot process the entire electromagnetic spectrum. We sense only a slice of it called visible light.
The light we see radiates from the sun, lightbulbs and other light sources in the form of microscopic particles called photons. When photons touch light-sensitive cells in the eyeball, they set off a chain reaction in the brain that leads to visualization.
Before we talk about the nerves and the brain, however, we have to talk about the optic mechanisms in the eyes that help send photons where they need to go to produce eyesight.
READ NEXT: Alice in Wonderland syndrome
Optical structures in human eyes
Our eyes capture photons bouncing off everything in our environment. When waves of photons bounce onto the eye, structures in the eyeball reroute them to specific locations. The primary optical structures are the:
Cornea – The curved, transparent tissue on the front of the eyeball bends light waves in a process called refraction. This process takes everything in our visual field and shrinks it down to a size our eyeballs can manage.
Iris – The colored portion of the eye contains melanin, the same substance that colors our hair and skin. This tint also filters sunlight in a way that improves visual functioning. Muscles in the iris manage the size of the pupil.
Pupil – The black circle in the center of the eye controls the volume of light waves that pass through the eyeball. Your pupils enlarge when visible light becomes scarce and narrow in response to bright lights or direct sunlight.
Lens – The transparent disc behind the cornea helps make our vision sharper. Tiny muscles around the lens change its shape to help us zero in on objects both near and far away.
Retina – This light-sensitive layer in the rear of the eyeball contains the building blocks of visualization: cells that sense light and color and then send visual information to the brain. The cornea and lens focus photons onto specific areas of the retina to produce sharp, clear images.
Though these parts of the eye are made of living tissue, they are similar to mechanical devices. Waves of photons trigger reactions in the same way that twisting a knob turns on your car’s headlights.
The rest of the story of visualization is much more complex because it involves bundles of nerves whose interactions are not fully understood.
Rods, cones, ganglia and optic nerves
Visualization starts taking shape in the retina. The retina is part of the central nervous system, which controls sensation, perception and muscular function.
The retina has two kinds of specialized light-sensitive nerve cells:
Rods, which help you see in low light and enable peripheral (side-to-side; up-and-down) vision.
Cones, which convey color and sharpen images at the eyeball’s center of vision.
Our eyes have millions of rods and cones that respond to photons by sending impulses to the ganglia, a network of neural cells that connect to the optic nerves.
Each eyeball has an optic nerve that transmits visual signals from the ganglia to the rear of the brain — a section called the occipital lobe. The right optic nerve sends signals to the left side of the occipital lobe, while the left optic nerve transmits to the right side.
These nerves meet at a junction called the optic chiasm. They continue along the optic tract until they begin to split apart at a site called the lateral geniculate nucleus. From here, the nerves connect to the brain’s visual centers.
Visualization culminates in the brain
The brain includes bundles of nerves dedicated to controlling vision. Visual data from the retina travels primarily to the brain’s occipital lobe. This is where the visual cortex begins translating light waves into eyesight.
Three other brain lobes also influence visualization:
Parietal – This lobe on the top half of the brain, immediately in front of the occipital lobe, helps us navigate through the world. Visual signals in the parietal lobe get translated into perceptions of depth and distance. This keeps us from crashing into things and promotes hand-eye coordination.
Temporal –This lobe on the bottom side of the brain, also in front of the occipital lobe, controls memory. Our memory centers give meaning to the images we perceive, enabling us to distinguish between a cat and a catalog, for instance.
Frontal – This lobe in the top front of the brain is a new frontier in the science of visualization. Long thought to have little role in eyesight, the frontal lobe is now believed to play a role in creating visual focus — dwelling on certain objects while ignoring other things.
For all we know about where visualization happens in the brain, the “why” of eyesight is not thoroughly understood. As an article in Quanta Magazine pointed out, vision is not a one-way street from the eyeball to the occipital lobe. It’s more like a massive collection of real-time feedback loops. The stuff we see now keeps interacting with lobes of the brain, which process all that we’ve seen before.
The complex nature of vision underscores the importance of attending to the more well-understood parts of visualization — the optical structures of the eye. Eye doctors can treat a vast array of vision problems with corrective lenses, medication, therapy and surgery. If you’re having trouble with vision, a visit to an eye doctor is the best way to figure out what’s going on and find a way to fix it.
READ NEXT: What is aphantasia?
Page published on Monday, March 8, 2021