The experiments were designed to determine whether the brains of the genetically altered mice could efficiently process sensory information from the new photoreceptors in their eyes. Among mammals, this more complex type of color vision has only been observed in primates, and therefore the brains of mice did not need to evolve to make these discriminations.

The new abilities of the genetically engineered mice indicate that the mammalian brain possesses a flexibility that permits a nearly instantaneous upgrade in the complexity of color vision, say the study's senior authors, Gerald Jacobs and Jeremy Nathans.