The most difficult things to imagine are those that go beyond the possibilities of sensation. Try, for example, to dream up a new hue, a new slice of the color pie. What would it look like?
Recently, mice have been genetically engineered to see in color.
Researchers then exposed the mutant, female mice to a light-discrimination test involving three colored panels—two of similar hues and the other differing in brightness or shading. After a significant training period—the researchers conducted well over 10,000 trials, rewarding mice who singled out the odd panel with a drop of soy-milk—three mice with the full complement of photo receptors were able to correctly finger the different panel 80 percent of the time. Normal mice, on the other hand, were only successful about one third of the time, a percentage equivalent to just randomly guessing.It's the closest experimental analogue to Frank Jackson's "Mary" hypothetical, or to Pleasantville, without the existential crisis--not because mice are incapable of such things, but because the mutants are born with the ability, so their new power isn't new to them.
Jacobs points out that not all of the mutant mice were able to successfully complete the color discrimination test, which he says could indicate how species deal with newly introduced abilities during evolution. He adds that the next step will be to determine how the brain incorporates the new color signals and makes the comparisons necessary to distinguish between different shades. "What this shows is that not only can you expand the range in which animals can sense stimuli," he asserts," but they can derive a new dimension of sensory experience."
And yet the empirical potential to open up a new avenue of color sensation doesn't make the imagining any easier. If there is a whole world of colors beyond our ken, to echo Thomas Nagel and paraphrase Donald Rumsfeld, it's a world of unknowable unknowns.