Background

Dichromats have only two working cone systems. Thus, they can see colors, though a much lesser range of colors than do trichromats. There are three major forms of dichromats, which include protanopes, deuteranopes, and tritanopes, missing the long, middle, and short wavelength cones, respectively. Dichromats require only two colored lights to match any monochromatic light as compared to trichromats, who require three. Dichromats see in color but cannot make some of the discriminations that are easy for trichromats. Protanopia and deuteranopia are linked to the X-chromosome and are therefore inheritable and more common in men than women. Protanopia and deuteranopia are also more common than tritanopia.

In this activity, you can remove one cone to create any type of dichromacy and see how it alters the appearance of different colors using the same layout as the Trichromatic Theory and Cone Responses activity.

Instructions

Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab

Settings

Below is a list of the ways that you can alter the model. The settings include the following:

Color: at the top are two squares. The left square is how the color looks to a person with trichromatic color vision, and the square on the right is a simulation how the same color looks to a person with the currently selected form of dichromacy. Choose Missing Cone: select which cone will be missing. Trichromat restores all cones.
Wavelength: change the wavelength of the light that is stimulating the cones. The wavelength is indicated by the vertical line in the cones graph on the left. The relative level of activity in each cone is shown in the bar graph. If a cone is missing, the curve for that cone and the bar are made fainter. They are absent in the dichromat.
Choose Wavelength: a set of preset wavelengths that you can choose that can help show the effects of different forms of dichromacy.

Reset

Pressing this button restores the settings to their default values.

Color

Choose Missing Cone: None Short Middle Long

Chose Wavelength (nm)           

The right hand image is seen by a trichromatic eye.

The graph on the left shows the sensitivity of the different cones to a wide range of visible wavelengths. The bar graph shows the relative level of activity of each of the three cone classes to the current wavelength. If a cone is removed, the relevant cone graph and bar for that cone's activities are faded out. The slide will allow you to select different wavelengths. The wavelength is indicated by the dark vertical line on the graph on the left.

The color patches at the top simulate the color for a person with trichromatic color vision and with the currently selected form of dichromacy.

Proceed to Quiz