The seventeenth-century British philosopher John Locke (1632–1704) may have gotten things started when he asked what the consequences would be “if the Idea, that a Violet produced in one Man’s Mind by his Eyes, were the same that a Marigold produces in another Man’s, and vice versa.” He suggested that the answer was not going to be readily forthcoming “because one Man’s Mind could not pass into another Man’s Body” (Locke, 1689/1975). Today, we would talk about the qualia (singular quale) of violet and marigold yellow, rather than the ideas. Qualia is the technical name for the subjective aspects of experiences like “violet” or “sweet” or “itch.”
The problem that Locke posed is often called the “inverted-spectrum” problem, though “inverted-qualia” problem might be more philosophically correct (Byrne, 2014). The problem is often posed by imagining that the subjective color qualia in a figure like textbook Figure 5.15 have been exchanged with the opponent color qualia on the other side of the color circle, though the pairing of names with specific physical stimuli would not change. Thus, a region that evoked the quale of “red” for you would evoke “green” for an invert, but that would just be his internal experience. He would have learned—as you learned—to call that experience “red,” so it would be very hard or, perhaps, impossible to tell that his subjective experience was the opposite of yours. The inverted-qualia idea and its variants can be used to discuss a range of significant philosophical issues, well beyond our scope here. This hypothetical situation can also be used to raise some interesting questions about our experience of color.
Look at textbook Figure 5.13D and think about the saturation axis of the HSB color space. What is the color halfway between a saturated red and the totally desaturated white or gray point? You would probably say “pink.” Now consider the other side of the color circle in that same figure. Halfway between green and white is something we might call “light green” or “pale green,” but we would not have a commonly accepted, unique color name for that experience. Think about our friend with the inverted qualia. Would “pink” make sense to him? Where we experience the quale “pink,” he would experience the quale “light green,” but pink is a distinct color with some special properties (Lindsey et al., 2010) while light green is not. Could we tell the difference between individuals with standard qualia and those with inverted qualia by carefully examining their responses to pink? Since inverts are most likely a philosophical invention, we can’t give an answer. However, raising the question helps us to understand that the relationship, between a mix of wavelengths reflected from the world and your subjective experience of color, might not be simple (Palmer, 1999).
Byrne, A. (Summer 2014 Edition). Inverted qualia. In E. N. Zalta (Ed.), The Stanford Encyclopedia of Philosophy, plato.stanford.edu/archives/sum2014/entries/qualia-inverted/.
Lindsey, D. T., Brown, A. M., Reijnen, E., Rich, A. N., Kuzmova, Y., and Wolfe, J. M. (2010). Color channels, not color appearance or color categories, guide visual search for desaturated color targets. Psychol Sci 21: 1208–1214.
Locke, J. (1689/1975). Essay Concerning Human Understanding, Oxford: Oxford University Press.
Palmer, S. E. (1999). Color, consciousness, and the isomorphism constraint. Behav Brain Sci 22: 923–943; discussion 944–989.
Qualia (sing. quale)
In reference to philosophy, private conscious experiences of sensation or perception.