[For this post, all links open in new windows.]

Look at graphs of the intensities of several light sources—LEDs, flourescent and incandescent light bulbs, sunlight—across the spectrum. (400 nm is around where violet begins to be visible to humans, 600 nm is orange, 800 nm is about where red stops being visible.) Consider how the differences between the shapes of the graphs correspond to your imaginations of the differences in appearance of an object under those different types of lights.

“Color stubs” at Wikipedia. Read the name of a color. Try to imagine that color, then click the link for that color’s entry. Consider how the color you see compares to how you had envisioned it. (Different experiences will be had with differently calibrated displays; for best experience, calibrate first.)

Consider that it is likely that some very small set of humans are “tetrachromats”—their eyes have four distinct types of cone cells, each type of which responds more strongly to particular wavelengths of radiation. The vast majority of people have only three types of these cells. Consider that no extra brain mechanism is thought to be needed simultaneously with the occurrence of the extra type of cone cells for the processing and integration of the extra sensory data from those cells to occur. Consider what the implications of this might be for the relationships between our sense organs and our experiences of sensations. Read about “qualia”.

Consider what it is like to be a bat. Consider what it is like to be a dog. Consider what it is like to be a computer… or whether attempting to consider such a thing is even rational. If not, why not? Can the rationality possibly change in the future if computers and the software that runs on them continue to become increasingly powerful?

Consider why you were born “as you” rather than as someone else. Is that question rational?