Background

While all trichromats have three classes of cone photopigments, not all have the same three classes of cone photopigments. Even in the range of people that are considered to have normal color vision, there are slight variations in the cone photopigments (Woods & Krantz, 2001).

There are color variations in trichromats that are more extreme and so they have not been called color normal. These are the anomalous trichromats. One of the three classes is significantly different from that found in normal, even considering the variation discussed in M- and L-cones. Let us learn to count a bit in ancient Greek. It is not as hard as it sounds. We number the cones 1, 2, and 3 starting with the L-cone. The M-cone is 2 and the S-cone is 3. In approximately ancient Greek and using the numbers as prefixes, 1 is prot-, 2 is deuter-, and 3 is trit-. The forms of anomalous trichromacy are protanomalous, deuteranomalous, or tritanomalous if the L-, M-, S-cone is the anomalous cone, respectively (Table 6.1 ). You can see the changes to the cones that occur in anomalous trichromacy in ISLE 6.12. One way that a person might experience anomalous trichromacy is that the tint of photos or videos might be a mightbit off. They will not discriminate quite as many colors, but the variation is overall relatively minor compared to those we next talk about next.

In this activity, you can make any one of the cone classes anomalous to examine any type of anomalous trichromacy 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 anomalous Trichromacy.
Choose Anomalous Cone: select which cone will be the anomalous form of the cone. Trichromat restores all cones to the more common type.
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 anomalous, the curve for that the more common form of the cone and the bar are made fainter. The anomalous form of the cone will be full on and this bar will be shown in the graph in the middle.  Compare the relative response of the more common and anomalous form of the cone.
Choose Wavelength: a set of preset wavelengths that you can choose that can help show the effects of different forms of anomalous trichromacy.

Reset

Pressing this button restores the settings to their default values.

Color

Choose Anomalous 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 in the middle shows the relative level of activity of each of the three cone classes to the current wavelength, indicated by the vertical line on the left hand sensitivity graph. If a cone is set to anomalous, the relevant cone graph and bar for the more common form of that cone's activities are faded out and the anomalous cones sensitivy curve and bar are shown. It is important to compare the two sensitivity curse and their different output to see the impact of being an anomalous trichromat.The slider 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 anomalous trichromacy.