VISION | Partielo

How Does Our Visual System Work?

Vision relies on the presence of light, which is a form of electromagnetic radiation characterized by its wavelength.

Humans can only detect a limited range of wavelengths, known as the visible spectrum, which spans from 380 to 750 nanometers.

The process of vision commences when light enters the eye through its protective covering.

In the eye, light first enters through the clear dome-shaped covering called the cornea.

Then, it moves through the central opening in the colored part of the eye, called the pupil.

After that, it passes through the eye's natural lens and a gel-like substance called vitreous humor, which fills most of the eye.

Light eventually reaches the retina at the back of the eye, where it gets turned into electrical signals.

The sharpest vision happens in a tiny spot on the retina called the fovea, which is about the size of a pinhead.

When you focus on something, your eyes move to place the image right on the pinhead-sized spot called the fovea. Even though the retina is very thin, it's made up of three layers of nerve cells.

2 pathways

The visual pathways in the brain are like roads that visual information travels on from our eyes to our brain.

These pathways are like separate roads in our brain for processing different aspects of what we see.

Sometimes, when people have problems with how they perceive things, like difficulty with coordination or recognizing objects, it suggests that these pathways are separate and specialized for different tasks.

It is because the information from the primary visual cortex in the occipital lobe is forwarded through two fasciculi (fiber bundles):
One ascends toward the parietal lobe (along the dorsal pathway), and one descends to the temporal lobe (along the ventral pathway)
The dorsal pathway is also called the where pathway and is responsible for processing location and motion information;
the ventral pathway is called the what pathway because it is mainly responsible for processing the color, shape, and identity of visual stimuli (Ungerleider & Haxby,1994; Ungerleider & Mishkin, 1982).

Theories of Color Vision

Three different photopigments recognized by cones
The trichromatic theory of color vision states that the color of any light is determined by the output of the three cone systems in our retina.

Young And Helmholtz Trichromatic Theory (cont.)

Each cone type contains a different photopigment and is thus sensitive to a different band of wavelengths.
The S-cone has a maximum response to light at 420nm (short wavelength). Blue
The M-cone has a maximum response to light at 535nm (medium wavelength). Green
The L-cone has a maximum response to light at 565nm (long wavelength). Red
The combinations of these three colors produce all of the colors that we are capable of perceiving.
When these three cone systems are combined, we can see color over a range of approximately 400 to 700nm.