Educational Resources

Eye and Vision Movies

Vision and The Human Eye

These materials and much more can be found on our (Physiology Of The Eye CD-ROM)

Anatomy of the Eye (Cross-sectional View)

Click on the words in the list below to learn about the major structures of the eye.

Cross-sectional view of the structures of the eye.


Embryonic Development of the Eye

QuickTime Watch the embryonic development of the vertebrate eye.

Color Theory and Perception

What is color?

spectral sensitivity of red-sensing cones

Red-sensing cones

spectral sensitivity of Green-sensing cones

Green-sensing cones

spectral sensitivity of Blue-sensing cones

Blue-sensing cones

Color is our perception of different wavelengths of light. Light visible to humans ranges in wavelength form 380 nanometers (nm) for violet light to 760 nm for red light.

The color spectrum visible to the human eye.

We have three types of cone photoreceptors. Each cone type responds to a different range of wavelengths within the visible light spectrum.

Red-sensitive cones are most stimulated by light in the red to yellow range.

Green-sensitive cones are maximally stimulated by light in the yellow to green range.

Blue-sensitive cones are maximally stimulated by blue and violet light.

Stimulation of different combinations of the three cone types can give the sensation of any color.

The Additive Color Theory.

Color vision in humans is based on the additive color theory. This theory states that all perceivable colors can be made by mixing different amounts of red, green, and blue light, the primary colors of the additive color system.

The additive color wheel.

The additive color wheel.

Equal amounts of the three primaries give the sensation of white, while the absence of additive primaries is black.

Additive color theory explains what we see when we look at a luminant object such as a light bulb, a TV, or a computer monitor. An ordinary incandescent light bulb emits light over most of the visible spectrum, but is strongest in the red to yellow range.

A standard "cool white" fluorescent bulb has a narrower emission profile than an incandescent bulb, producing more light in the green to blue range.

The screen of a TV or a computer monitor is made of millions of red, green, and blue phosphors closely packed together. When stimulated by a high voltage, groups of phosphors glow to create an image on the screen. Millions of colors can be created by combining phosphors of these three primary colors.


Optical Illusions

Kanisza subjective contour floating triangle illusion.

Do you see a white triangle defined by three black circles? Roll your mouse over the figure above to see how much of this perception is "real" and how much is imagined.

A whiter-than-white triangle is clearly seen in Kanizsa's figure (above). Close inspection of this illusion reveals that there aren't any lines separating the triangle from the white background of the screen. Yet, a clear line is created in our minds. Figures defined by imaginary lines such as these are known as subjective contour illusions.

One theory suggests that specialized contour-detecting cells in the brain are activated by these short line segments. Additional processing in the brain would "connect" the segments to form a continuous line.

Subjective Illusions

Kanisza subjective circles line illusion.
A subjective circle.

Kanisza subjective circle or square illusion.
Do you see circles or squares?

Kanisza subjective floating dots on triangle image.
Do the black dots seem to
float on top of the triangle?

Kanisza subjective transparent surface subjective contour illusion.
A transparent surface is suggested
by the subjective contour.

More eye and vision info...