(Land color effect / Benham’s Disk / Opponent-process theory)
In this section, Feynman discusses Land color effect, Benham’s Disk (Fechner colors), and opponent-process theory of color vision that are related to subjective
sensation of colors. For example, Fechner colors could be defined as the creation of
illusory (subjective) colors through a repeated pattern of black and white
stimulus. Thus,
the section could be specified as “the subjective sensation of color.”
1. Land color effect:
“In fact, Land has shown that if we mix that
apparent blue and the red in various proportions, by using two photographic
transparencies with absorption in front of the red and the white in different
proportions, it can be made to represent a real scene, with real objects,
rather faithfully. In this case we get a lot of intermediate apparent colors
too, analogous to what we would get by mixing red and blue-green; it seems to
be an almost complete set of colors, but if we look very hard at them, they are
not so very good. Even so, it is surprising how much can be obtained from just
red and white (Feynman et
al., 1963, p. 36–1).”
Edwin Land’s two-color experiment
involving white light and red light was a pioneering experiment in color
vision. Specifically, Land
was using two black-and-white transparencies of the same colored-scene: the
first transparency was taken through a red filter and the second transparency
was taken through a green filter (See figure below). In other words, one may emphasize the need
of illuminating a photograph (long record) with longer wavelengths of light and
the photograph (short record) with shorter wavelengths of light (Land, 1959). The experiment demonstrates that,
through the mixing of red and white light, observers could perceive a variety
of intermediate colors, creating the illusion of a broad color spectrum. Importantly,
Land’s
experiment could not be explained by classical color theory principles, which need
three primary colors to form a wide gamut of colors.
Source: Land, 1959
Note:
Edwin H. Land was the inventor of instant photography or Polaroid camera.
According to some writers, e.g., Erik Calonius, Steve Jobs was inspired by
Land. In his biography of Steve Jobs, Isaacson (2011) quotes Jobs as saying
that Land was one of his heroes.
Edwin
Land proposed the retinex theory of color vision, which requires the brain’s
interpretation of relative differences in light reflected from surfaces instead
of the intensity of light that reaches the eyes. The word “retinex” is a mix of “retina” and
“cortex,” meaning that both the eye and the brain are involved in the sensing of
color. The theory was also used to explain the phenomenon of color constancy under a wide range
of lighting conditions. In actual
scenes, the perceived color of each region depends on the colors of its
neighboring points and the overall color of the scene. Essentially, Land’s experiment seek to understand
whether color is inherent in the physical world or it is a subjective sensation
of human eye.
2. Benham's Disk:
“Another
example is the appearance of “colors” in a black-and-white rotating disc,
whose black and white areas are as shown in Fig. 36–1. When
the disc is rotated, the variations of light and dark at any one radius are
exactly the same; it is only the background that is different for the two kinds
of “stripes.” Yet one of the “rings” appears colored with one color and the
other with another (Feynman et
al., 1963, p. 36–1).”
At
the end of the previous lecture, Feynman discussed the phenomenon of Fechner
colors*. The color
effect is also known as the Benham’s Top or Benham's Disk, which involves the sensation
of colors when an object with black-and-white pattern is rotated. The sensation
of colors depends on several factors, such as the speed of rotation, i.e., the
brain interprets colors due to the integration and motion of the
black-and-white pattern. For example, if the disk
(as shown below) is rotated clockwise, the innermost arcs may form red rings,
the inner arcs may form orange rings, the outer arcs may form green rings, and
the outermost arcs may form blue rings. If it is rotated anticlockwise, the
pattern is reversed, with the innermost arcs form blue rings and the outermost
red rings. Brighter
light conditions may result in more vivid or saturated colors, while dimmer
light may lead to less distinct colors or grayscale appearance.
Source: Nishiyama, 2014.
*In the Audio Recordings of the previous lecture, Feynman
says something like: “It is comparing what it sees in one region
with another not in the conscious way, but already in retinal level and this is
demonstrated by this crazy color phenomenon known as the Fechner colors.”
Source: The Feynman Lectures
Audio Collection: https://www.feynmanlectures.caltech.edu/flptapes.html
“No one yet understands the
reason for those colors, but it is clear that information is being put together
at a very elementary level, in the eye itself, most likely (Feynman et al., 1963, p. 36–1).”
The Pattern Induced
Flicker Colors (PIFC) model and Yutaka Nishiyama’s Dynamic Interference model, e.g.,
offer explanations for the phenomenon observed in Benham's disk, but they
approach it from different perspectives. Firstly, the PIFC model suggests that
the sensation of colors in Benham’s disk arises from interactions between
different types of retinal cells and neural circuits. It proposes that the
alternating black and white patterns on the disk stimulate different types of
retinal cells differently, leading to the sensation of colors. On the other
hand, the interference model attributes the perception of colors in Benham’s
disk to interference patterns generated within the visual system. It suggests
that the black and white patterns on the disk create interference patterns as
they move across the retina. Both models offer insights into the complex
processes underlying the sensation of colors in Benham’s disk.
3.
Opponent
process theory:
“The
fact that there are three pigments does not mean that there must be three kinds
of sensations. One of the other theories of color vision has it that there are
really opposing color schemes. That is, one of the nerve fibers carries
a lot of impulses if there is yellow being seen, and less than usual for blue.
Another nerve fiber carries green and red information in the same way, and
another, white and black (Feynman et
al., 1963, p. 36–2).”
Perhaps Feynman could have used the term “opponent
process theory of color vision” instead of opposing color schemes. Historically, Ewald Hering, a German physiologist,
made significant contributions to this color theory in the late 19th century. Hering
suggested that color vision involves three sets of receptors (red-green,
blue-yellow, black-white) where these pairs of colors cannot be perceived
simultaneously. (For example, a cell was excited by green light would be
inhibited by red light, and vice versa.) It was proposed to understand the
observation of color afterimages, where staring at one color for an extended
period leads to the perception of its complementary color after looking away.
It implies that we cannot sense greenish reds or yellowish-blues as colors. In
a sense, the theory was based on Hering’s belief that
Helmholtz was unable to give a good physiological explanation for
color-contrasted phenomena (Finger,
2001).
“In
the modern literature all we find on the subject are repeats of the same
statement, or of one by a German psychologist, who uses as one of his
authorities Leonardo da Vinci, who, of course, we all know was a great artist.
He says, ‘Leonardo thought there were five colors’ (Feynman et al., 1963, p. 36–2).”
Perhaps Feynman could have
identified the German psychologist that says, “Leonardo thought there were five
colors.” However, Leonardo da Vinci writes, “White is given by light,
without which no color may
be seen, yellow by earth, green by water, blue by air and red by fire, and
black by darkness which stands above the element of fire, because there is
no substance or dimension on which the rays are able to percuss and accordingly
to illuminate it (cited in Hoeppe, 2007, p. 59).” In short, da Vinci thought
there were six colors: white, yellow (earth), green (water), blue (air), red
(fire) and black. However, da Vinci was inconsistent and sometimes did not include black and
white as colors (Kuehni & Schwarz, 2008).
Review
Questions:
1.
How would you explain the Land color effect?
2. How would you explain the Fechner colors?
3. How
would you explain the opponent process
theory of color vision?
The
moral of the lesson: the subjective color sensation of the human eye
can be demonstrated through various optical phenomena, such as Land’s two-color experiment,
Benham’s disk, and color afterimages.
References:
1. Feynman, R. P., Leighton, R. B., & Sands, M. (1963). The Feynman Lectures on Physics, Vol I: Mainly mechanics, radiation, and
heat. Reading, MA: Addison-Wesley.
2. Finger, S.
(2001). Origins of neuroscience: a history of explorations into brain
function. Oxford University Press.
3. Hoeppe, G. (2007). Why the sky is
blue: discovering the color of life. Princeton, New Jersey: Princeton
University Press.
4. Kuehni, R. G., &
Schwarz, A. (2008). Color ordered: a survey of color systems from
antiquity to the present. New York: Oxford University Press.
5. Land, E. H. (1959). Experiments in color vision. Scientific American, 200(5), 84-99.
6. Isaacson, W. (2011). Steve Jobs. New York: Simon and Schuster.
7. Nishiyama, Y. (2014). The Mathematics of
Benham’s Top. International Journal of Pure and Applied Mathematics, 93(3), 399.
