Mice are rewarded if they correctly pick the color that differs from the other two. Only mice with an extra photoreceptor can distinguish certain colors.
Mice with Enhanced Color Vision
Mice engineered to have a third photoreceptor can distinguish more colors than normal mice
Source: “Emergence of Novel Color Vision in Mice Engineered to Express a Human Cone Photopigment”
Gerald H. Jacobs et al.
Science 315(5819): 1723-1725
Results: Researchers from Johns Hopkins University and the University of California, Santa Barbara, used genetic engineering to breed mice that have three kinds of photoreceptors, as humans do, instead of two, as mice normally do. After lengthy training, the mice were able to distinguish colors that normal mice could not.
Why it matters: Since the result required only genetically induced changes of the photoreceptors and no tweaking of the underlying neural circuitry, the findings suggest that the sensory system is very plastic and can learn to use entirely new information. This could explain how primates, the only animals with trichromatic color vision, developed their color-sensing abilities. Primates may have taken advantage of the extra visual information granted by a new photoreceptor without evolving specialized wiring in the brain.
Methods: Researchers engineered mice to express the gene for a photo-sensing protein that can detect red light, which mice usually can’t distinguish from green. In behavioral tests, the mice were shown three circles of colored light–two of the same color and one of a different color distinguishable to humans but not to normal mice. After intensive training during which the mice were rewarded for selecting the different color, scientists found that mice with the extra sensor could tell the colors apart while their normal counterparts could not.
Next Steps: Researchers plan to investigate how the visual system in the engineered mice adapted to take advantage of the new information.