Biology 202
2001 Second Web Report
On Serendip

Imagine yourself in an art museum. You wander slowly from cold room to cold room, analyzing colored canvases on stark white walls. When you reach a particular work, do you prefer to stand back and take everything in at once? Or do you move so close to the painting that the individual brushstrokes become apparent? Several different sensory processes occur in your brain during this trip to the art museum; the majority of them involve visual inputs. How does your brain put together all the information that your eyes receive? This raises questions ranging from depth of field to color. The ideas of color perception and color theory are interesting ones. How do humans account for color and does it truly exist? I think that by examining not only the neurological on-goings in the brain, but by learning about color through philosophy, and even art, a greater understanding of it can be reached.

Before delving into the philosophy of color and the questions posed by different pieces of art, the biological basis process of HOW color is seen should be explained. The retina is a neural sheet, containing the photoreceptors called rods and cones that is located at the back of the eye. Between the retina and the optic nerves leading to the brain are a series of cells that create a lateral inhibition network of the light/dark signals from the photoreceptors (1). This throws away a lot of the information generated by the photocells and gives the brain a "picture" of the edges of light and dark. The contrasts are created, leaving the brain to fill in the rest. Color vision is even more complex. Cones (the light adapted photoreceptor) contain three different photopigments, red, green, and blue, each corresponding to a particular wavelength of light (2). Color is a property of three things: the ratio of red/green activation, blue response, and value or lightness (3). The brain utilizes visual inputs to determine each of these, thus generating the characteristic color.

One of the most important (and most interesting) conclusions of the biology of vision is that color is not technically generated by physical reality. Color appears to be a mental construct, and therefore, everyone views color differently. The rationale one is often given for the color of particular objects is the following: light consists of all colors. When light strikes an object in absorbs most of the wavelengths of light, but those that it reflects correspond to the color one sees. For example, light hits an apple, it absorbs all the wavelengths of light except red light, which is reflected and perceived by the eye (4). A deeper analysis shows that this explanation is not necessarily true, red is not always red. Referring to the earlier description of the anatomy of color vision one should note that there are not the same number of photopigments in the eye as there are number of colors. In fact, the color "red" is not produced only by light of "red" wavelength. There are three different photopigments in the eye, and it is the ratio of activation between each of these pigments that generates the unique signal, which one's brain construes as "red" (2). This property of color vision allows for some unique concepts and questions, leading into discussion of more theoretical ideas about color.

Let's return to the art museum, particularly a room full of Impressionist paintings. All the canvases seem to exhibit a glow, a kind of brightness, whether they are by Monet, Degas, or Seurat. Colors can take on a different appearance depending on the context in which they are viewed. It is not that these artists were the using different kinds of paint, but that their placement and choices of color (specifically color saturation and value) create an incredible lightness that other works lack. Impressionists were one of the first groups of painters who consciously took the idiosyncrasies of color perception into account. They used not just the colors of pigments, but the "colors" of light in their work. Think of Seurat's Sunday Afternoon on the Island of la Grande Jatte or Monet's Waterlilies and the difference between viewing the painting from a distance and up-close. Seurat uses a technique called pointillism, where paint of different colors are placed next to each other, but generate a completely different "color" in the brain. A red dot beside a green dot is read as "yellow" by the photoreceptors in the eye. What is the mental "leap" between the physicality of these two distinct color pigments and the perceived "color" of the image seen? Obviously Seurat did not want viewers of his work to see a canvas full of opposite color dots, but a cohesive image. This distinction between pigment color and light color is quite interesting.

Colors are made mentally by the brain's varying response to hue (color), saturation (intensity), and value (light/dark). Each color also is defined by its reflectance curve, which graphs how the photopigments in the eye activate in response to it (3). In elementary school art classes children learn that the primary colors are red, blue, and yellow. From these three all the colors in the world can be created: red and yellow make orange, yellow and blue make green. Color mixing in this case is subtractive, and does not fit with the biological description, as the photopigments in the eye "correspond" to red, green, and blue. Mixing of colored light is additive (5). Perceived red light and perceived yellow light do not mix to form orange light. Yellow, is instead, created by red and green light, as was stated in the description of Seurat's painting. How does the brain know to switch from additive color mixing to subtracting color mixing so that perception is not only coherent, but also accurate and consistent? In places where an Impressionist painter could have easily just used yellow paint, there is red paint next to green. Why?

Teaching color theory and art seems to be counter-intuitive, especially when you consider that color vision, and therefore experiencing art, is subjective. Viewers of art will never know if how they see a work mirrors the artist's intended vision. Maybe that is the reason why humans find art so compelling, so personal. A message is conveyed from the artist's mind/experience to a canvas to the viewer's eye. Like a game of Telephone, it is probable that the original has been changed in some way during its path from artist to observer. Looking at all the questions this paper raises, one thing seems to be true: color perception is not totally understood. Those studying the philosophy of mind seem to be interested in the representational states and perceptual states of color, generating a variety of opinions on the subject. What causes the mind to associate the mental construct of color with physical objects(6)? Though it is not necessary for that trip to the art museum, attempting to understand all of the intricacies of the colored world definitely makes looking at paintings more cerebral and more interesting.

WWW Sources

2)How We See Colors, An interesting site providing information on different types of sensory processing by the Howard Hughes Medical Institute.

3)Handprint: Color Vision, Extremely useful site that gives detailed descriptions of different color theory terminology. Also provides reflectance curves for several common color pigments that are often used in art. This is the site for the neuroscientist in artists.

4)Color Matters-Vision-How the eye sees color, This site gives some basic information about color and vision, including the "apple" description of seeing red.

5)Color/Color Vision, A table of contents of different links to interesting color questions, including descriptions of color mixing.

6)Dictionary of Philosophy of Mind-theories of color, This site provides philosophical definitions and arguments in the debate about how color is perceived and why it is perceived in this fashion.

| Course Home Page | Forum | Brain and Behavior | Serendip Home |