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How We See

How We See

Description:

This lesson will introduce you to the anatomy and physiology of the human visual system, its connection to the brain and how this system processes light.

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Tutorial

What's Covered

Hi, and welcome to today's lesson on how you see. Today’s lesson will introduce the anatomy and the physiology of the human visual system, it's connection to the brain, and how this system processes light. Specifically, you will learn about:

  1. Structure of the Eye
  2. How the Eye Functions
  3. The Eye & The Brain

1. Structure of the Eye

The human eye is a complex sensory organ and it's designed to see light and color, which plays an important part in the visual communication process. Currently there's a lot that we do understand about this process, but it's still very incomplete, and there's plenty of visual research ongoing.


So above is an image of the side cut to the eye. The retina is a thin transparent tissue at the back of the eye that contains light sensitive receptors called the rods and cones.

Terms to Know

    • Retina
    • A thin, transparent tissue at the back of the eye that contains light sensitive receptors called rods and cones.
  • Rods
  • The long, thin light sensitive parts of the retina that processes night vision.
  • Cones
  • The light sensitive parts of the retina that processes color and day vision.

Rods are the long, thin, light-sensitive parts of the retina that process night vision. Cones are the light-sensitive parts of the retina that process color and day vision. There are a lot of these in the eyes, in the retina, anywhere from 120 million rods and 6 or 7 million cones.


2. How the Eye Functions

So what happens is you see an image, and light passes through the eye lens and hits the retina. In the retina, those rods and cones create nerve impulses and convert light into electrical signals, which travel through the brain through the optic nerve. And the optic nerve is the tissue that connects the retina to the visual cortex in the back of the brain, which I'll show you here in a minute.

Terms to Know

    • Optic Nerve
    • Tissue that connects the retina to the visual cortex in the back of the brain.
    • Visual Cortex
    • The part of the brain which processes visual information from the retina, communicated via a network of nerve cells.

3. The Eye & The Brain

If you look at the side cut of a face below, you can see the image of the eye from earlier and a nice view of the brain.

So light hits the retina with your cones and rods, and that information travels through the optic nerve, which routes it to the lateral geniculate nucleus, which then routes to the lower back side of the brain called the visual cortex, which is the part of the brain which processes visual information from the retina communicated via network of nerve cells.

Now, there's a lot of complexity to the way we process images and light. And it continues with electromagnetic radiation. Electromagnetic radiation is another name for light, which is why we got here. The human eye is only sensitive to a portion of it known as visible light. So light travels in waves and all electromagnetic radiation or light travels at the same speed, which refer to as the speed of light. When we talk about light traveling in waves, we also talk about frequency, which is the number of waves passing a certain point per second, measured in Hertz. Light can be characterized by its wavelength.

Terms to Know

    • Wavelength
    • The measure of the distance from two consecutive waves crests or troughs, commonly measured in nanometers.
    • Electromagnetic Radiation
    • Another name for light; the human eye is only sensitive to a portion of it, known as visible light.
    • Frequency
    • The number of waves passing a certain point per second, measured in hertz.

Example The human eye can see wavelengths somewhere between 400 and 900 nanometers, which is what is referred to as visible light within the electromagnetic spectrum. So light waves with a shorter wavelength and a higher frequency are beyond the human eye's visibility range. That'll be things like gamma, x-rays, and ultraviolet light. Likewise, infrared, microwaves, and radio waves have longer wavelengths and longer frequencies, and are also beyond what the human eye can see.


Summary

That concludes today’s lesson on the human eye and how you see. Specifically, you learned about the structure and function of the human eye, as well as the eye’s connection to the brain.

Keep up the learning and have a great day!

Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR MARIO E. HERNANDEZ

TERMS TO KNOW
  • Rods

    The long, thin light sensitive parts of the retina that processes night vision.

  • Cones

    The light sensitive parts of the retina that processes color and day vision.

  • Retina

    A thin, transparent tissue at the back of the eye that contains light sensitive receptors called rods and cones.

  • Visual Cortex

    The part of the brain which processes visual information from the retina, communicated via a network of nerve cells.

  • Optic Nerve

    Tissue that connects the retina to the visual cortex in the back of the brain.

  • Wavelength

    The measure of the distance from two consecutive waves crests or troughs, common measured in nanometers.

  • Frequency

    The number of waves passing a certain point per second, measured in hertz.

  • Electromagnetic Radiation

    Another name for light; the human eye is only sensitive to a portion of it, known as visible light.